MPFR(3)

NAME
Math::MPFR - perl interface to the MPFR (floating point) library.

DEPENDENCIES
   This module needs the MPFR and GMP C libraries. (Install the
   GMP library first as it is a pre-requisite for MPFR.)

   The GMP library is available from https://gmplib.org .
   The MPFR library is available from https://www.mpfr.org .

   Documentation for current mpfr functions can be found at:
   www.mpfr.org/mpfr-current/mpfr.html#Function-and-Type-Index .

DESCRIPTION
   A bigfloat module utilising the MPFR library. The main aim of
   this module is to wrap the floating point functions provided
   by that library. We also access many of those functions via
   operator overloading. (A small number of customised functions,
   not found in the MPFR library, are also available.)

SYNOPSIS
   # This synopsis is very brief. My attempts at providing a
   # reasonable coverage in this section always result in
   # something that is ridiculously complex :-(

   use Math::MPFR qw(:mpfr);

   # Create a Math::MPFR object with an assigned value. The
   # returned object will have current default precision, and
   # the value will be rounded according to current dwfault
   # rounding mode. In this example, we provide a string as the
   # argument, but non-string arguments are also permitted.

   my $rop = Math::MPFR->new('1.2e-10');

   # Other ways of assigning a string using new() to create an
   # equivalent Math::MPFR object include:
   # my $rop = Math::MPFR->new('1.2@-10');
   # my $rop = Math::MPFR->new("1.2\@-10");
   # Octal (base 8):
   # my $rop = Math::MPFR->new('1.0176077644330267e-11', 8);
   # my $rop = Math::MPFR->new('0x1.07e1fe91b0b7p-33');
   # Specify base (16) if '0x' prefix is not provided:
   # my $rop = Math::MPFR->new('1.07e1fe91b0b7p-33', 16);

   # Display the value held by $rop.
   print $rop;                  # 1.2e-10

   # Other ways of printing out the value include:
   # print mpfrtoa($rop);       # 1.2e-10
   # Rmpfr_printf("%Rg", $rop); # 1.2e-10

ROUNDING MODE
   As of mpfr-3.0.0, the rounding values are:
    MPFR_RNDN (numeric value = 0): Round to nearest.
    MPFR_RNDZ (numeric value = 1): Round towards zero.
    MPFR_RNDU (numeric value = 2): Round towards +infinity.
    MPFR_RNDD (numeric value = 3): Round towards -infinity.

   Previously they were named (respectively) GMP_RNDN,
    GMP_RNDZ, GMP_RNDU and GMP_RNDD.

   You can use either the "GMP_*" or the "MPFR_*" renditions,
   but the former is discouraged.

   Also available are:
    mpfr-3.0.0 and later:
      MPFR_RNDA (numeric value = 4): Round away from zero.
    mpfr-4.0.0 and later:
      MPFR_RNDF (numeric value = 5): Faithful rounding.

    These last two rounding modes will cause a fatal error
    if the mpfr library against which Math::MPFR has been
    built is not sufficiently recent.

    MPFR_RNDF is experimental - the computed value is either
    that corresponding to MPFR_RNDD or that corresponding to
    MPFR_RNDU. In particular when those values are identical,
    i.e., when the result of the corresponding operation is
    exactly representable, that exact result is returned.
    Thus, the computed result can take at most two possible
    values, and in absence of underflow/overflow, the
    corresponding error is strictly less than one ulp (unit in
    the last place) of that result and of the exact result.
    For MPFR_RNDF, the returned value and the inexact flag are
    unspecified, the divide-by-zero flag is as with other
    roundings, and the underflow and overflow flags match what
    would be obtained in the case the computed value is the
    same as with MPFR_RNDD or MPFR_RNDU. The results may not
    be reproducible, and it may not work with all functions.
    Please report bugs.

    MPFR_RNDN (the 'round to nearest' mode) works as in the
    IEEE P754 standard: in case the number to be rounded
    lies exactly in the middle of two representable
    numbers, it is rounded to the one with the least
    significant bit set to zero.  For example, the
    number 5, which is represented by '101' in binary,
    is rounded to '10p1' (4) with a precision of two bits,
    and not to '11p1' (6).  This rule avoids the "drift"
    phenomenon mentioned by Knuth in volume 2 of
    The Art of Computer Programming (section 4.2.2,
    pages 221-222).

    Most Math::MPFR functions take as first argument the
    destination variable, as second and following arguments
    the input variables, as last argument a rounding mode,
    and have a return value of type 'int'. If this value
    is zero, it usually means that the value stored in the
    destination variable is the exact result of the
    corresponding mathematical function. If the returned
    value is positive (resp. negative), it usually means
    the value stored in the destination variable is greater
    (resp. lower) than the exact result.  For example with
    the 'GMP_RNDU' rounding mode, the returned value is
    usually positive, except when the result is exact, in
    which case it is zero.  In the case of an infinite
    result, it is considered as inexact when it was
    obtained by overflow, and exact otherwise.  A
    NaN result (Not-a-Number) always corresponds to an
    inexact return value.

   See also the Rmpfr_round_nearest_away() function in the
   ROUNDING MODE FUNCTIONS section for the mode
   "round to nearest, ties away from zero".

MEMORY MANAGEMENT
   Objects are created with new() or with the Rmpfr_init*
   functions. All of these functions return an object that has
   been blessed into the package Math::MPFR.
   They will therefore be automatically cleaned up by the
   DESTROY() function whenever they go out of scope.

   For each Rmpfr_init* function there is a corresponding function
   called Rmpfr_init*_nobless which returns an unblessed object.
   If you create Math::MPFR objects using the '_nobless'
   versions, it will then be up to you to clean up the memory
   associated with these objects by calling Rmpfr_clear($op)
   for each object, or Rmpfr_clears($obj1, $obj2, ....).
   Alternatively such objects will be cleaned up when the script
   ends. Because these objects created by the '_nobless' functions
   have not been blessed into the Math::MPFR package, the
   overloaded operators will not work with them.

MIXING GMP OBJECTS WITH MPFR OBJECTS
   Some of the Math::MPFR functions below take as arguments
   one or more of the GMP types mpz (integer), mpq
   (rational) and mpf (floating point). (Such functions are
   marked as taking mpz/mpq/mpf arguments.)
   For these functions to work you need to have loaded either:

   1) Math::GMP from CPAN. (This module provides access to mpz
      objects only - NOT mpf and mpq objects.)

   AND/OR

   2) Math::GMPz (for mpz types), Math::GMPq (for mpq types)
      and Math::GMPf (for mpf types).

PASSING __float128 VALUES
   There are 3 ways to pass __float128 values to/from
   Math::MPFR. Option 1) is the preferred option:

    1) Build perl (5.21.4 or later) with -Dusequadmath; build the
    mpfr-4.0.0 (or later) library with the configure option
    --enable-float128. Then build Math::MPFR in the usual way.
    If the build process does not then result in a Math::MPFR
    module that supports the __float128 NV try providing the
    "F128=1" arg to the Makefile.PL (which will define the symbol
    MPFR_WANT_FLOAT128):

      perl Makefile.PL F128=1

    (And please file a bug report, because the aim is that you
    should not need to specify F128=1 here.)

    Then you can pass your perl's __float128 NV values directly
    to/from Math::MPFR using:

      Rmpfr_set_float128() or Rmpfr_set_NV() and
      Rmpfr_get_float128() or Rmpfr_get_NV()

    This will also mean that overloaded operations that receive an
    NV will evaluate that (__float128) NV to its full precision.
    And assigning the NV as Math::MPFR->new($NV) will also work as
    intended.

    NOTE:
      If you have built perl with -Dusequadmath, but the mpfr
      library was not built with float128 support , then both
      Rmpfr_set_NV() and Rmpfr_get_NV() will still set/get
      __float128 values.
      Also, overloaded operations that receive an NV will still
      evaluate that (__float128) NV to its full precision.
      It's only Rmpfr_set_float128() and Rmpfr_get_float128() that
      will not be available.

    2) On a perl that was not built with -Dusequadmath, install
    Math::Float128, build the mpfr-4.0.0 (or later) library with
    the configure option --enable-float128, and build Math::MPFR
    by providing the "F128=1" arg to the Makefile.pl:

      perl Makefile.PL F128=1

    Then you can pass the values of the Math::Float128 objects to
    and from Math::MPFR objects using:

      Rmpfr_set_FLOAT128() and Rmpfr_get_FLOAT128()

    3) Convert the __float128 values to a string and pass them to
    and from Math::MPFR using:

      Rmpfr_strtofr()/Rmpfr_set_str() and Rmpfr_get_str()

PASSING _Decimal64 & _Decimal128 VALUES
   Install Math::Decimal64 and/or Math::Decimal128 and build the mpfr
   library (version 3.1.0 or later for _Decimal64, version 4.1.0 or
   later for _Decimal128) with the --enable-decimal-float option. The
   Math::MPFR build process should detect the _Decimal64/_Decimal128
   availability and include or exclude the support accordingly.

   If the auto-detection fails to detect the availability, you can
   override it by providing the "D64=1" and/or "D128=1" arg to the
   the Makefile.PL (either of which will define
   MPFR_WANT_DECIMAL_FLOATS):

     perl Makefile.PL D64=1 D128=1

   You can then pass _Decimal64/_Decimal128 values between Math::MPFR
   and Math::Decimal64/Math::Decimal128 using:

      Rmpfr_set_DECIMAL64() and Rmpfr_get_DECIMAL64()
      Rmpfr_set_DECIMAL128() and Rmpfr_get_DECIMAL128()

   NOTE: It is allowable to pass any or all of "D64=1", "D128=1" and
        "F128=1" args to the Makefile.PL.

  To force the removal of _Decimal64/Decimal128 support in
  Math::MPFR, simply provide "D64=0" and/or "D128=0" as arguments to
  the Makefile.PL:

      perl Makefile.PL D64=0 D128=0

FUNCTIONS
   The following functions are generally wrappers around an mpfr
   function of the same name. eg. Rmpfr_swap() is a wrapper around
   mpfr_swap().

   "$rop", "$op1", "$op2", etc. are Math::MPFR objects.

   "$inex" is a signed integer value (IV) returned by many of the
   mpfr functions.
   $inex == 0 indicates that the function's result was exact;
   $inex < 0 indicates that the function's result was rounded to a
     value that is less than the exact result;
   $inex > 0 indicates that the function's result was rounded to a
     a value that is greater than the exact result.

   "$ui" means any integer that will fit into a C 'unsigned long int',

   "$si" means any integer that will fit into a C 'signed long int'.

   "$uj" means any integer that will fit into a C 'uintmax_t'. Don't
   use any of these functions unless your perl's UV is at least as big
   as a 'uintmax_t'.

   "$sj" means any integer that will fit into a C 'intmax_t'. Don't
   use any of these functions unless your perl's IV is at least as big
   as an 'intmax_t'.

   "$double" is a C double and "$float" is a C float ... but both will
   be represented in Perl as an NV.

   "$ld" means a long double. Don't use these functions if the precision
   of your Perl's NV is less than the precision of a 'long double'.

   "$f128" means a __float128. Don't use these functions unless your
   Perl's NV is a __float128 && mpfr has been configured with
   '--enable-float128'. (Note that versions of mpfr prior to 4.0.0
   cannot be configured with '--enable-float128'.)

   "$bool" means a value (usually a 'signed long int') in which
   the only interest is whether it evaluates as false or true.

   "$str" simply means a string of symbols that represent a number,
   eg '1234567890987654321234567E7' or 'zsa34760sdfgq123r5@11'.
   Valid bases for MPFR numbers are 2 to 62.

   "$rnd" is simply one of the 5 rounding mode values (discussed above)
    that many of the functions require as their rounding arg. In my
    code, rather than providing them as a perl scalar, I usually write
    them in their bareword form - MPFR_RNDN or MPFR_RNDU or ..., etc.

   "$p" is the (signed int) value for precision.

   ##############

   ROUNDING MODE FUNCTIONS

   Rmpfr_set_default_rounding_mode($rnd);
    Sets the default rounding mode to $rnd (where $rnd can be one of
    MPFR_RNDN, MPFR_RNDU, MPFR_RNDZ, MPFR_RNDD and MPFR_RNDA.
    Note that MPFR_RNDA is available only if Math::MPFR has been built
    against mpfr-3.0.0 or later.
    The default rounding mode is to nearest initially (MPFR_RNDN).
    The default rounding mode is the rounding mode that is used in
    in overloaded operations.

   $si = Rmpfr_get_default_rounding_mode();
    Returns to $si the numeric value (0, 1, 2, 3 or 4) of the
    current default rounding mode. This will initially be 0.

   $inex = Rmpfr_prec_round($rop, $p, $rnd);
    Rounds $rop according to $rnd with precision $p, which may be
    different from that of $rop.  If $p is greater or equal to the
    precision of $rop, then new space is allocated for the mantissa,
    and it is filled with zeroes.  Otherwise, the mantissa is rounded
    to precision $p with the given direction. In both cases, the
    precision of $rop is changed to $p. The precision $p can be any
    integer between RMPFR_PREC_MIN and RMPFR_PREC_MAX.

   $inex = Rmpfr_round_nearest_away(\&function, $rop, @input_args);
    This is a perl implementation (and not a wrapping) of
    the mpfr_round_nearest_away macro introduced in
    mpfr-4.0.0. You can use this function so long as
    Math::MPFR has been built against mpfr-3.0.0 or later.
    This rounding is defined in the same way as MPFR_RNDN,
    except in case of tie, where the value away from zero is
    returned.
    The first arg is a reference to the perl subroutine you
    wish to call, and the remaining args are the args that
    the subroutine usually takes (minus the rounding arg).
    For example:

    $inex = Rmpfr_round_nearest_away(\&Rmpfr_add, $rop,
                                    $op1, $op2);

    $inex = Rmpfr_round_nearest_away(\&Rmpfr_strtofr, $rop,
                                    '1e-200', 10);

    $inex = Rmpfr_round_nearest_away(\&Rmpfr_prec_round,
                                    $rop, $prec);

    The "function" being called must be one that returns the
    ternary int (-ve for "less than", 0 for "exact", and +ve for
    "greater than").

    Unlike the more efficient rndna(), this function requires that
    Rmpfr_get_emin() is greater than Rmpfr_get_emin_min().
    If you're not concerned about correct rounding (nearest away) of
    the value +/- 0.25 * (2 ** Rmpfr_get_emin()) then you can instead
    use the rndna function (immediately below).

   $inex = rndna(\&function, $rop, @input_args);
    A more efficient version of the (above) Rmpfr_round_nearest_away
    function. However, it will not correctly deal with the value
    +/- 0.25 * (2 ** Rmpfr_get_emin()).
    Unlike Rmpfr_round_nearest_away(), this function allows that
    Rmpfr_get_emin() == Rmpfr_get_emin_min().

   ##############

   INITIALIZATION

   A variable should be initialized once only.

   First read the section 'MEMORY MANAGEMENT' (above).

   Rmpfr_set_default_prec($p);
    Set the default precision to be *exactly* $p bits.  The
    precision of a variable means the number of bits used to store its
    mantissa.  All subsequent calls to 'mpfr_init' will use this
    precision, but previously initialized variables are unaffected.
    This default precision is set to 53 bits initially.  The precision
    can be any integer between RMPFR_PREC_MIN and RMPFR_PREC_MAX.

   $ui = Rmpfr_get_default_prec();
    Returns the default MPFR precision in bits.

   $rop = Math::MPFR->new();
   $rop = Math::MPFR::new();
   $rop = new Math::MPFR();
   $rop = Rmpfr_init();
   $rop = Rmpfr_init_nobless();
    Initialize $rop, and set its value to NaN. The precision
    of $rop is the default precision, which can be changed
    by a call to 'Rmpfr_set_default_prec'.
    NOTE: The new() sub can accept an argument - in which case
          $rop is initialized and the given value assigned to it.
          If the argument is a Math::GMP or Math::GMPz or Math::GMPq
          object then the returned Math::MPFR object's value is set
          in accordance with current default precision and current
          default rouding mode.
          If the argument is a PV then a second optional argument
          specifying the numeric base of the string is permitted.
          See COMBINED INITIALIZATION AND ASSIGNMENT below for
          more details.

   $rop = Rmpfr_init2($p);
   $rop = Rmpfr_init2_nobless($p);
    Initialize $rop, set its precision to be *exactly* $p bits,
    and set its value to NaN.  To change the precision of a
    variable which has already been initialized,
    use 'Rmpfr_set_prec' instead.  The precision $p can be
    any integer between RMPFR_PREC_MIN and RMPFR_PREC_MAX.

   @rops = Rmpfr_inits($how_many);
   @rops = Rmpfr_inits_nobless($how_many);
    Returns an array of $how_many Math::MPFR objects - initialized,
    with a value of NaN, and with default precision.
    (These functions do not wrap mpfr_inits.)

   @rops = Rmpfr_inits2($p, $how_many);
   @rops = Rmpfr_inits2_nobless($p, $how_many);
    Returns an array of $how_many Math::MPFR objects - initialized,
    with a value of NaN, and with precision of $p.
    (These functions do not wrap mpfr_inits2.)

   Rmpfr_set_prec($op, $p);
    Reset the precision of $op to be *exactly* $p bits.
    The previous value stored in $op is lost.  The precision
    $p can be any integer between RMPFR_PREC_MIN and
    RMPFR_PREC_MAX. If you want to keep the previous
    value stored in $op, use 'Rmpfr_prec_round' instead.

   $si = Rmpfr_get_prec($op);
    Return to $si the precision actually used for assignments of $op,
   i.e. the number of bits used to store its mantissa.

   Rmpfr_set_prec_raw($rop, $p);
    Reset the precision of $rop to be *exactly* $p bits.  The only
    difference with 'mpfr_set_prec' is that $p is assumed to be small
    enough so that the mantissa fits into the current allocated
    memory space for $rop. Otherwise an error will occur.

   $min_prec = Rmpfr_min_prec($op);
    (This function is implemented only when Math::MPFR is built
    against mpfr-3.0.0 or later. The mpfr_min_prec function was
    not present in earlier versions of mpfr.)
    $min_prec is set to the minimal number of bits required to store
    the significand of $op, and 0 for special values, including 0.
   (Warning: the returned value can be less than RMPFR_PREC_MIN.)

   $minimum_precision = RMPFR_PREC_MIN;
   $maximum_precision = RMPFR_PREC_MAX;
    Returns the minimum/maximum precision for Math::MPFR objects
    allowed by the mpfr library being used.

   ##########

   ASSIGNMENT

   $inex = Rmpfr_set($rop, $op, $rnd);
   $inex = Rmpfr_set_ui($rop, $ui, $rnd);
   $inex = Rmpfr_set_si($rop, $si, $rnd);
   $inex = Rmpfr_set_sj($rop, $sj, $rnd);
   $inex = Rmpfr_set_uj($rop, $uj, $rnd);
   $inex = Rmpfr_set_IV($rop, $iv, $rnd); # $iv is $Config{ivtype}
   $inex = Rmpfr_set_d ($rop, $double, $rnd);
   $inex = Rmpfr_set_ld($rop, $ld, $rnd); # long double
   $inex = Rmpfr_set_NV($rop, $nv, $rnd); # $nv is $Config{nvtype}
   $inex = Rmpfr_set_LD($rop, $LD, $rnd); # $LD is a Math::LongDouble
                                          # object
   $inex = Rmpfr_set_z($rop, $z, $rnd); # $z is a mpz object.
   $inex = Rmpfr_set_q($rop, $q, $rnd); # $q is a mpq object.
   $inex = Rmpfr_set_f($rop, $f, $rnd); # $f is a mpf object.
   $inex = Rmpfr_set_flt($rop, $nv, $rnd);      # mpfr-3.0.0 and later only
                                                # Set $rop to the value of
                                                # $nv rounded to a float.
   $inex = Rmpfr_set_float16($rop, $nv, $rnd);  # mpfr-4.3.0 and later only
                                                # & only on 64-bit systems.
   $inex = Rmpfr_set_bfloat16($rop, $nv, $rnd); # mpfr-4.3.0 and later only
                                                # & only on 64-bit systems.
   $inex = Rmpfr_set_float128($rop, $f128, $rnd);# nvtype is __float128
                                               # && mpfr-4.0.0 or later
                                               # && mpfr lib built with
                                               # --enable-float128.
   $inex = Rmpfr_set_DECIMAL64($rop, $D64, $rnd);# mpfr-3.1.0 or later &&
                                               # mpfr lib built with
                                               # --enable-decimal-float
                                               # $D64 is a
                                               # Math::Decimal64 object
   $inex = Rmpfr_set_DECIMAL128($rop, $D128, $rnd);# mpfr-3.1.0 or later &&
                                               # mpfr lib built with
                                               # --enable-decimal-float.
                                               # $D128 is a
                                               # Math::Decimal128 object
   $inex = Rmpfr_set_FLT($rop, $FLT, $rnd); # Set $rop to the value of
                                            # the Math::Float32 object $FLT.
   $inex = Rmpfr_set_FLOAT16($rop, $F16, $rnd); # Set $rop to the value of the
                                                # Math::Float16 object $F16
   $inex = Rmpfr_set_BFLOAT16($rop, $BF16, $rnd);# Set $rop to the value of the
                                                 # Math::Bfloat16 object $BF16
   $inex = Rmpfr_set_FLOAT128($rop, $F128, $rnd);# mpfr-4.0.0 and later
                                               # && mpfr lib built with
                                               # --enable-float128.
                                               # $F128 is a
                                               # Math::Float128 object.
    Set the value of $rop from 2nd arg, rounded to the precision of
    $rop towards the given direction $rnd.  Please note that even a
    'long int' may have to be rounded if the destination precision
    is less than the machine word width.  The return value is zero
    when $rop==2nd arg, positive when $rop>2nd arg, and negative when
    $rop<2nd arg.  For 'mpfr_set_d', be careful that the input
    number $double may not be exactly representable as a double-precision
    number (this happens for 0.1 for instance), in which case it is
    first rounded by the C compiler to a double-precision number,
    and then only to a mpfr floating-point number.
    Rmpfr_set_float16 and Rmpfr_set_bfloat are currently unavailable to
    32-bit systems. Where enabled, these 2 functions set $rop to the value
    of the given NV argument, rounded (according to $rnd) to a _Float16
    or (respectively) a __bf16.

    NOTE:
         1) Rmpfr_set_IV requires that $iv has it's IOK flag set, and
         Rmpfr_set_NV requires that $nv has its NOK flag set.
         Otherwise these functions will croak.
         Best to first check IOK_flag($iv) or NOK_flag($nv), both of which
         will return a non-zero value if and only if the flag in question
         is set.

         2) Rmpfr_set_IV also handles unsigned (UV) arguments.

   $inex = Rmpfr_set_ui_2exp($rop, $ui, $exp, $rnd);
   $inex = Rmpfr_set_si_2exp($rop, $si, $exp, $rnd);
   $inex = Rmpfr_set_uj_2exp($rop, $sj, $exp, $rnd);
   $inex = Rmpfr_set_sj_2exp($rop, $sj, $exp, $rnd);
   $inex = Rmpfr_set_z_2exp($rop, $z, $exp, $rnd); # mpfr-3.0.0 & later only
    Set the value of $rop from the 2nd arg multiplied by two to the
    power $exp, rounded towards the given direction $rnd.  Note that
    the input 0 is converted to +0. ($z is a GMP mpz object.)

   $iv = Rmpfr_set_str($rop, $str, $base, $rnd);
    Set $rop to the value of $str in base $base (0,2..36) or, if
    Math::MPFR has been built against mpfr-3.0.0 or later, (0,2..62),
    rounded in direction $rnd to the precision of $rop.
    The exponent is read in decimal.  This function returns 0 if
    the entire string is a valid number in base $base. Otherwise
    it returns -1.
    If -1 is returned:
      1) the non-numeric flag (which was initialised to 0) will be
         incremented. You can query/clear/reset the value of the
         flag with (resp.) nnumflag()/clear_nnum()/set_nnum() - all
         of which are documented below (in "MISCELLANEOUS");
      2) A warning will be emitted if $Math::MPFR::NNW is set to 1
        (default is 0).
    If $base is zero, the base is set according to the following
    rules:
     if the string starts with '0b' or '0B' the base is set to 2;
     if the string starts with '0x' or '0X' the base is set to 16;
     otherwise the base is set to 10.
    The following exponent symbols can be used:
     '@' - can be used for any base;
     'e' or 'E' - can be used only with bases <= 10;
     'p' or 'P' - can be used to introduce binary exponents with
                  hexadecimal or binary strings.
    See the MPFR library documentation for more details. See also
    'Rmpfr_inp_str' (below).
    Because of the special significance of the '@' symbol in perl,
    make sure you assign to strings using single quotes, not
    double quotes, when using '@' as the exponent marker. If you
    must use double quotes (which is hard to believe) then you
    need to escape the '@'. ie the following two assignments are
    equivalent:
     Rmpfr_set_str($rop, '.1234@-5', 10, GMP_RNDN);
     Rmpfr_set_str($rop, ".1234\@-5", 10, GMP_RNDN);
    But the following assignment won't do what you want:
     Rmpfr_set_str($rop, ".1234@-5", 10, GMP_RNDN);

   $inex = Rmpfr_strtofr($rop, $str, $base, $rnd);
    This function differs from Rmpfr_set_str() mainly in that it
    returns the usual "exactness" ternary value ($inex).
    Read a floating point number from a string $str in base $base,
    rounded in the direction $rnd. If successful, the result is
    stored in $rop. If $str doesn't start with a valid number then
    $rop is set to zero.
    Parsing follows the standard C 'strtod' function with some
    extensions.  Case is ignored. After optional leading whitespace,
    one has a subject sequence consisting of an optional sign ('+' or
    '-'), and either numeric data or special data. The subject
    sequence is defined as the longest initial subsequence of the
    input string, starting with the first non-whitespace character,
    that is of the expected form.
    The form of numeric data is a non-empty sequence of significand
    digits with an optional decimal point, and an optional exponent
    consisting of an exponent prefix followed by an optional sign and
    a non-empty sequence of decimal digits. A significand digit is
    either a decimal digit or a Latin letter (62 possible characters),
    with 'a' = 10, 'b' = 11, ..., 'z' = 36; its value must be strictly
    less than the base.  The decimal point can be either the one
    defined by the current locale or the period (the first one is
    accepted for consistency with the C standard and the practice, the
    second one is accepted to allow the programmer to provide MPFR
    numbers from strings in a way that does not depend on the current
    locale).  The exponent prefix can be 'e' or 'E' for bases up to
    10, or '@' in any base; it indicates a multiplication by a power
    of the base. In bases 2 and 16, the exponent prefix can also be
    'p' or 'P', in which case it introduces a binary exponent: it
    indicates a multiplication by a power of 2 (there is a difference
    only for base 16).  The value of an exponent is always written in
    base 10.  In base 2, the significand can start with '0b' or '0B',
    and in base 16, it can start with '0x' or '0X'.

    If the argument $base is 0, then the base is automatically detected
    as follows. If the significand starts with '0b' or '0B', base 2 is
    assumed. If the significand starts with '0x' or '0X', base 16 is
    assumed. Otherwise base 10 is assumed. Other allowable values for
    $base are 2 to 62.

    Note: The exponent must contain at least a digit. Otherwise the
    possible exponent prefix and sign are not part of the number
    (which ends with the significand). Similarly, if '0b', '0B', '0x'
    or '0X' is not followed by a binary/hexadecimal digit, then the
    subject sequence stops at the character '0'.
    Special data (for infinities and NaN) can be '@inf@' or
    '@nan@(n-char-sequence)', and if BASE <= 16, it can also be
    'infinity', 'inf', 'nan' or 'nan(n-char-sequence)', all case
    insensitive.  A 'n-char-sequence' is a non-empty string containing
    only digits, Latin letters and the underscore (0, 1, 2, ..., 9, a,
    b, ..., z, A, B, ..., Z, _). Note: one has an optional sign for
    all data, even NaN.

   Rmpfr_set_inf($rop, $si);
   Rmpfr_set_nan($rop);
   Rmpfr_set_zero($rop, $si); # mpfr-3.0.0 and later only.
    Set the variable $rop to infinity or NaN (Not-a-Number) or zero
    respectively. In 'Rmpfr_set_inf' and 'Rmpfr_set_zero', the sign of
    $rop is positive if 2nd arg >= 0. Else the sign is negative.

   Rmpfr_swap($op1, $op2);
    Swap the values $op1 and $op2 efficiently. Warning: the precisions
    are exchanged too; in case the precisions are different, 'mpfr_swap'
    is thus not equivalent to three 'mpfr_set' calls using a third
    auxiliary variable.

   ################################################

   COMBINED INITIALIZATION AND ASSIGNMENT

   NOTE: Do NOT use these functions if $rop has already
   been initialised. Use the Rmpfr_set* functions in the
   section 'ASSIGNMENT' (above).

   First read the section 'MEMORY MANAGEMENT' (above).

   $rop = Math::MPFR->new($arg);
   $rop = Math::MPFR::new($arg);
   $rop = new Math::MPFR($arg);
    Returns a Math::MPFR object with the value of $arg, rounded
    in the default rounding direction, with default precision.
    $arg can be either a number (signed integer, unsigned integer,
    signed fraction or unsigned fraction), a string that
    represents a numeric value, or an object (of type Math::GMPf,
    Math::GMPq, Math::GMPz, orMath::GMP) If $arg is a string, an
    optional additional argument that specifies the base of the
    number can be supplied to new(). Legal values for base are 0
    and 2 to 62. If $arg is a string and no additional argument is
    supplied, the base will be deduced.
    See 'Rmpfr_set_str' above for an explanation of how that
    deduction is made, and for rules regarding the string format.

    NOTE: If $arg is *both* an NV (floating point value) and PV
    (string), then the value specified by the PV (string) will be
    used. This is probably what you want (less likely so with
    perl-5.18.4 and earlier).
    However, there's no guaranteed way for the new() function to
    correctly tell and it's best to avoid passing such values, or
    to explicitly use the value you want by doing an Rmpfr_init()
    followed by the appropriate 'Rmpfr_set_*' function documented in
    the previous section. Or, if such exists, you could instead call
    the appropriate 'Rmpfr_init_set_*' function documented
    immediately below.
    Note that these functions (below) return a list of 2 values.

   ($rop, $inex) = Rmpfr_init_set        ($op, $rnd);
   ($rop, $inex) = Rmpfr_init_set_nobless($op, $rnd);
   ($rop, $inex) = Rmpfr_init_set_ui        ($ui, $rnd);
   ($rop, $inex) = Rmpfr_init_set_ui_nobless($ui, $rnd);
   ($rop, $inex) = Rmpfr_init_set_si        ($si, $rnd);
   ($rop, $inex) = Rmpfr_init_set_si_nobless($si, $rnd);
   ($rop, $inex) = Rmpfr_init_set_d        ($double, $rnd);
   ($rop, $inex) = Rmpfr_init_set_d_nobless($double, $rnd);
   ($rop, $inex) = Rmpfr_init_set_ld        ($ld, $rnd);
   ($rop, $inex) = Rmpfr_init_set_ld_nobless($ld, $rnd);
   ($rop, $inex) = Rmpfr_init_set_float128        ($f128, $rnd);
   ($rop, $inex) = Rmpfr_init_set_float128_nobless($f128, $rnd);
   ($rop, $inex) = Rmpfr_init_set_f        ($f, $rnd);# $f is a mpf object
   ($rop, $inex) = Rmpfr_init_set_f_nobless($f, $rnd);# $f is a mpf object
   ($rop, $inex) = Rmpfr_init_set_z        ($z, $rnd);# $z is a mpz object
   ($rop, $inex) = Rmpfr_init_set_z_nobless($z, $rnd);# $z is a mpz object
   ($rop, $inex) = Rmpfr_init_set_q        ($q, $rnd);# $q is a mpq object
   ($rop, $inex) = Rmpfr_init_set_q_nobless($q, $rnd);# $q is a mpq object
   ($rop, $inex) = Rmpfr_init_set_IV        ($IV,$rnd);# $IV is $Config{ivtype}
   ($rop, $inex) = Rmpfr_init_set_IV_nobless($IV,$rnd);# $IV is $Config{ivtype}
   ($rop, $inex) = Rmpfr_init_set_NV        ($NV,$rnd);# $NV is $Config{nvtype}
   ($rop, $inex) = Rmpfr_init_set_NV_nobless($NV,$rnd);# $NV is $Config{nvtype}

    Initialize $rop and set its value from the 1st arg, rounded to
    direction $rnd. The precision of $rop will be taken from the
    active default precision, as set by 'Rmpfr_set_default_prec'.

   ($rop, $si) = Rmpfr_init_set_str($str, $base, $rnd);
   ($rop, $si) = Rmpfr_init_set_str_nobless($str, $base, $rnd);
    Initialize $rop and set its value from $str in base $base,
    rounded to direction $rnd. If $str was a valid number, then
    $si will be set to 0. Else it will be set to -1.
    If $si is -1 :
      1) the non-numeric flag (which was initialised to 0) will be
         incremented. You can query/clear/reset the value of the
         flag with (resp.) nnumflag()/clear_nnum()/set_nnum() - all
         of which are documented below (in "MISCELLANEOUS");
      2) A warning will be emitted if $Math::MPFR::NNW is set to 1
        (default is 0).
     See 'Rmpfr_set_str' (above) and 'Rmpfr_inp_str' (below).

   ##########

   CONVERSION

   $str = Rmpfr_get_str($op, $base, $digits, $rnd);
    Returns a string of the form, eg, '8.3456712@2'
    which means '834.56712'. The "mantissa" portion fo the returned
    string will be presented in base $base. The "exponent" portion will
    be in base 10. $digits specifies the number of digits required
    to be output in the mantissa. (Trailing zeroes are removed.)
    If $digits is 0, the number of digits of the mantissa is chosen
    large enough so that re-reading the printed value with the same
    precision, assuming both output and input use rounding to nearest,
    will recover the original value of $op.
    $str will be set to 'Nan', '-Inf' or 'Inf' whenever $op is
    (respectively) a NaN, a negative infinity or a positive infinity.

   ($str, $si) = Rmpfr_deref2($op, $base, $digits, $rnd);
    Returns the mantissa to $str (as a string of base $base digits,
    prefixed with a minus sign if $op is negative), and returns the
    exponent to $si as a base 10 value. There's an implicit decimal
    point to the left of the first digit in $str. $digits specifies
    the number of digits required to be output in the mantissa.
    If $digits is 0, the number of digits of the mantissa is chosen
    large enough so that re-reading the printed value with the same
    precision, assuming both output and input use rounding to nearest,
    will recover the original value of $op.
    Unlike Rmpfr_get_str() and Rmpfr_integer_string(), $str will be set
    to '@NaN@', '-@Inf@' or '@Inf@' whenever $op is (respectively) a
    NaN, a negative infinity or a positive infinity, as those are the
    strings that the mpfr library assigns.

   $str = Rmpfr_integer_string($op, $base, $rnd);
    Returns the truncated integer value of $op as a string. (No exponent
    is returned). For example, if $op contains the value 2.3145679e2,
    $str will be set to "231".
    $str will be set to 'Nan', '-Inf' or 'Inf' whenever $op is
    (respectively) a NaN, a negative infinity or a positive infinity.

   $bool = Rmpfr_fits_ushort_p($op, $rnd);  # fits in unsigned short
   $bool = Rmpfr_fits_sshort_p($op, $rnd);  # fits in signed short
   $bool = Rmpfr_fits_uint_p($op, $rnd);    # fits in unsigned int
   $bool = Rmpfr_fits_sint_p($op, $rnd);    # fits in signed int
   $bool = Rmpfr_fits_ulong_p($op, $rnd);   # fits in unsigned long
   $bool = Rmpfr_fits_slong_p($op, $rnd);   # fits in signed long
   $bool = Rmpfr_fits_uintmax_p($op, $rnd); # fits in uintmax_t
   $bool = Rmpfr_fits_intmax_p($op, $rnd);  # fits in intmax_t
   $bool = Rmpfr_fits_IV_p($op, $rnd);      # fits in perl IV or UV
    Return non-zero if $op would fit in the respective data
    type, when rounded to an integer in the direction $rnd.

   $ui = Rmpfr_get_ui($op, $rnd);
   $si = Rmpfr_get_si($op, $rnd);
   $sj = Rmpfr_get_sj($op, $rnd); # Available only when ivtype is 'long long'.
   $uj = Rmpfr_get_uj($op, $rnd); # Available only when ivtype is 'long long'.
   $IV = Rmpfr_get_IV($op, $rnd); # $IV is $Config{ivtype}
    Convert $op to an 'unsigned long long', a 'signed long', a
    'signed long long', an 'unsigned long long' or an 'IV' - after
    rounding it with respect to $rnd.
    If $op is NaN, the result is undefined. If $op is too big
    for the return type, it returns the maximum or the minimum
    of the corresponding C type, depending on the direction of
    the overflow. The flag erange is then also set.

   $double = Rmpfr_get_d($op, $rnd);
   $ld     = Rmpfr_get_ld($op, $rnd);
   $f128   = Rmpfr_get_float128($op, $rnd);# nvtype is __float128
                                           # && mpfr-4.0.0 or later
                                           # && mpfr lib built with
                                           # --enable-float128.
   $NV = Rmpfr_get_NV     ($op, $rnd);   # double/long double/__float128
   $NV = Rmpfr_get_flt    ($op, $rnd);   # mpfr-3.0.0 and later.
                                         # Set $NV to $op rounded to float.
   $NV = Rmpfr_get_float16($op, $rnd);   # mpfr-4.3.0 and later, and
                                         # only on 64-bit systems.
   $NV = Rmpfr_get_bfloat16($op, $rnd);  # mpfr-4.3.0 and later, and
                                         # only on 64-bit systems.
   Rmpfr_get_FLT($FLT, $op, $rnd);       # Set the Math::Float32 object $FLT
                                         # to the float value of $op.
   Rmpfr_get_FLOAT16($F16, $op, $rnd);   # Set the Math::Float16 object $F16
                                         # to the _Float16 value of $op.
   Rmpfr_get_BFLOAT16($F16, $op, $rnd);  # Set the Math::Bfloat16 object $F16
                                         # to the __bf16 value of $op.
   Rmpfr_get_LD($LD, $op, $rnd);         # $LD is a Math::LongDouble object.
   Rmpfr_get_DECIMAL64($d64, $op, $rnd); # mpfr-3.1.0 or later &&
                                         # mpfr lib built with
                                         # --enable-decimal-float
                                         # && D64=1 arg given to
                                         # Makefile.PL. $D64 is a
                                         # Math::Decimal64 object
   Rmpfr_get_FLOAT128($F128, $op, $rnd);# mpfr-4.0.0 and later &&
                                        # mpfr library built with
                                        # --enable-float128.
                                        # $F128 is a Math::Float128
                                        # object.
    Convert $op to a 'double', a 'long double', a '__float128', an 'NV',
    a 'float', a '_Float16', a '__bf16', a Math::Float32 object, a
    Math::Float16 object, a Math::Bfloat16 object, a Math::LongDouble
    object, a Math::Decimal64 object, or a Math::Float128 object using
    the rounding mode $rnd.
    Rmpfr_get_float16 and Rmpfr_get_bfloat16 are currently unavailable to
    32-bit systems. Where enabled they actually return an NV that has been
    set to the exact value of $op rounded (according to $rnd) to a _Float16
    or (respectively) a __bf16.

   $double = Rmpfr_get_d1($op);
    Convert $op to a double, using the default MPFR rounding mode.
    THIS FUNCTION IS DEPRECATED.
    Instead, do:
    $double = Rmpfr_get_d($op, Rmpfr_get_default_prec());

   $si = Rmpfr_get_z_exp($z, $op);  # $z is a mpz object
   $si = Rmpfr_get_z_2exp($z, $op); # $z is a mpz object
    (Identical functions. Use either - 'get_z_exp' might one day
    be removed.)
    Puts the mantissa of $rop into $z, and returns the exponent
    $si such that $rop == $z * (2 ** $ui).

   $inex = Rmpfr_get_z($z, $op, $rnd); # $z is a mpz object.
    Convert $op to an mpz object ($z), after rounding it with respect
    to RND. If built against mpfr-3.0.0 or later, return the usual
    ternary value. (The function returns undef when using mpfr-2.x.x.)
    Croak with appropriate error message if $op is NaN or Inf.

   $inex = Rmpfr_get_f ($f, $op, $rnd); # $f is a Math::GMPf object.
    Convert $op to a 'mpf_t', after rounding it with respect to $rnd.
    When built against mpfr-3.0.0 or later, this function returns the
    usual ternary value. When built against earlier versions of mpfr,
    return zero if no error occurred.
    Croak with appropriate error message if $op is NaN or Inf.

   Rmpfr_get_q ($q, $op); # $q is a Math::GMPq object.
    Convert $op to a rational value. $q will be set to the exact
    value contained in $op - hence no need for a rounding argument.
    Croak with appropriate error message if $op is NaN or Inf.

   $d = Rmpfr_get_d_2exp ($exp, $op, $rnd); # $d is NV (double)
   $d = Rmpfr_get_ld_2exp ($exp, $op, $rnd); # $d is NV (long double)
    Set $exp and $d such that 0.5<=abs($d)<1 and $d times 2 raised
    to $exp equals $op rounded to double (resp. long double)
    precision, using the given rounding mode.  If $op is zero, then a
    zero of the same sign (or an unsigned zero, if the implementation
    does not have signed zeros) is returned, and $exp is set to 0.
    If $op is NaN or an infinity, then the corresponding double
    precision (resp. long-double precision) value is returned, and
    $exp is undefined.

   $inex = Rmpfr_frexp($si, $rop, $op, $rnd); # mpfr-3.1.0 and later only
    Set $si and $rop such that 0.5<=abs($rop)<1 and $rop * (2 ** $si)
    equals $op rounded to the precision of $rop, using the given
    rounding mode. If $op is zero, then $rop is set to zero (of the same
    sign) and $exp is set to 0. If $op is  NaN or an infinity, then $rop
    is set to the same value and the value of $exp is meaningless (and
    should be ignored).

   $ui1 = Rmpfr_get_str_ndigits($ui2, $ui3); # new with mpfr-4.1.0
     Note: $ui2 must be in the range 2..62 (inclusive).
     Return the minimal integer $ui1 such that any number of precision
     $ui3 bits, when output with $ui1 digits in radix $ui2 with rounding
     to nearest, can be recovered exactly when read again, still with
     rounding to nearest.
     More precisely, we have $ui1 = 1 + ceil($ui3 * log(2) / log($ui2)),
     with $ui3 decremented by 1 if $ui2 is a power of 2.
     This function wraps mpfr_get_str_ndigits if mpfr version is 4.1.0
     or later. Otherwise it calls Rmpfr_get_str_ndigits_alt, which does
     not require mpfr-4.1.0.

   $ui1 = Rmpfr_get_str_ndigits_alt($ui2, $ui3);
     Provided as a fallback (though it can also be called separately)
     for Rmpfr_get_str_ndigits when mpfr version is older than 4.1.0.
     Unlike Rmpfr_get_str_ndigits, this function does not require that
     $ui2 is in the range 2..62.

   ##########

   ARITHMETIC

   $inex = Rmpfr_add($rop, $op1, $op2, $rnd);
   $inex = Rmpfr_add_ui($rop, $op, $ui, $rnd);
   $inex = Rmpfr_add_si($rop, $op, $si1, $rnd);
   $inex = Rmpfr_add_d($rop, $op, $double, $rnd);
   $inex = Rmpfr_add_z($rop, $op, $z, $rnd); # $z is a mpz object.
   $inex = Rmpfr_add_q($rop, $op, $q, $rnd); # $q is a mpq object.
    Set $rop to 2nd arg + 3rd arg rounded in the direction $rnd.
    The return  value is zero if $rop is exactly 2nd arg + 3rd arg,
    positive if $rop is larger than 2nd arg + 3rd arg, and negative
    if $rop is smaller than 2nd arg + 3rd arg.

   $inex = Rmpfr_sum($rop, \@ops, scalar(@ops), $rnd);
    @ops is an array consisting entirely of Math::MPFR objects.
    Set $rop to the sum of all members of @ops, rounded in the direction
    $rnd. $si is zero when the computed value is the exact value, and
    non-zero when this cannot be guaranteed, without giving the direction
    of the error as the other functions do.

   $inex = Rmpfr_sub($rop, $op1, $op2, $rnd);
   $inex = Rmpfr_sub_ui($rop, $op, $ui, $rnd);
   $inex = Rmpfr_sub_z($rop, $op, $z, $rnd);  # $z is a mpz object.
   $inex = Rmpfr_z_sub($rop, $z, $op, $rnd);  # mpfr-3.1.0 and later only
   $inex = Rmpfr_sub_q($rop, $op, $q, $rnd);  # $q is a mpq object.
   $inex = Rmpfr_ui_sub($rop, $ui, $op, $rnd);
   $inex = Rmpfr_si_sub($rop, $si1, $op, $rnd);
   $inex = Rmpfr_sub_si($rop, $op, $si1, $rnd);
   $inex = Rmpfr_sub_d($rop, $op, $double, $rnd);
   $inex = Rmpfr_d_sub($rop, $double, $op, $rnd);
    Set $rop to 2nd arg - 3rd arg rounded in the direction $rnd.
    The return value is zero if $rop is exactly 2nd arg - 3rd arg,
    positive if $rop is larger than 2nd arg - 3rd arg, and negative
    if $rop is smaller than 2nd arg - 3rd arg.

   $inex = Rmpfr_mul($rop, $op1, $op2, $rnd);
   $inex = Rmpfr_mul_ui($rop, $op, $ui, $rnd);
   $inex = Rmpfr_mul_si($rop, $op, $si1, $rnd);
   $inex = Rmpfr_mul_d($rop, $op, $double, $rnd);
   $inex = Rmpfr_mul_z($rop, $op, $z, $rnd);   # $z is a mpz object.
   $inex = Rmpfr_mul_q($rop, $op, $q, $rnd);   # $q is a mpq object.
    Set $rop to 2nd arg * 3rd arg rounded in the direction $rnd.
    Return 0 if the result is exact, a positive value if $rop is
    greater than 2nd arg times 3rd arg, a negative value otherwise.

   $inex = Rmpfr_div($rop, $op1, $op2, $rnd);
   $inex = Rmpfr_div_ui($rop, $op, $ui, $rnd);
   $inex = Rmpfr_ui_div($rop, $ui, $op, $rnd);
   $inex = Rmpfr_div_si($rop, $op, $si1, $rnd);
   $inex = Rmpfr_si_div($rop, $si1, $op, $rnd);
   $inex = Rmpfr_div_d($rop, $op, $double, $rnd);
   $inex = Rmpfr_d_div($rop, $double, $op, $rnd);
   $inex = Rmpfr_div_z($rop, $op, $z, $rnd);   # $z is a mpz object.
   $inex = Rmpfr_z_div($rop, $z, $op, $rnd);   # $z is a mpz object.
   $inex = Rmpfr_div_q($rop, $op, $q, $rnd);   # $q is a mpq object.
   $inex = Rmpfr_q_div($rop, $q, $op, $rnd);   # $q is a mpq object.
    NOTE: The mpfr library does not provide mpfr_z_div and
           mpfr_q_div functions.
    Set $rop to 2nd arg / 3rd arg rounded in the direction $rnd.
    These functions return 0 if the division is exact, a positive
    value when $rop is larger than 2nd arg divided by 3rd arg,
    and a negative value otherwise.

   q_add_fr($q1, $q2, $op); # $q1, $q2 are mpq objects
    Set $q1 to the exact rational value of $q2 + $op.

   q_sub_fr($q1, $q2, $op); # $q1, $q2 are mpq objects
    Set $q1 to the exact rational value of $q2 - $op.

   q_mul_fr($q1, $q2, $op); # $q1, $q2 are mpq objects
    Set $q1 to the exact rational value of $q2 * $op.

   q_div_fr($q1, $q2, $op); # $q1, $q2 are mpq objects
    Set $q1 to the exact rational value of $q2 % $op.

   q_fmod_fr($q1, $q2, $op); # $q1, $q2 are mpq objects
    Set $q1 to the exact rational value of fmod($q2,$op).

   $inex = Rmpfr_sqr($rop, $op, $rnd);
    Set $rop to the square of $op, rounded in direction $rnd.

   $inex = Rmpfr_sqrt($rop, $op, $rnd);
   $inex = Rmpfr_sqrt_ui($rop, $ui, $rnd);
    Set $rop to the square root of the 2nd arg rounded in the
    direction $rnd. Set $rop to NaN if 2nd arg is negative.
    Return 0 if the operation is exact, a non-zero value otherwise.

   $inex = Rmpfr_rec_sqrt($rop, $op, $rnd);
    Set $rop to $op ** (-1 / 2) rounded in the direction $rnd. Set
    $rop to +Inf if $op is 0, and 0 if $op is +Inf. Set $rop to NaN
    if $op is less than zero.

   $inex = Rmpfr_rec_root($rop, $op, $ui, $rnd);
    NOTE: There is no such mpfr function as mpfr_rec_root.
    This function originally provided as a perl implementation by
    Vincent Lefevre - and rewritten by sisyphus as an XSub.
    (See https://sympa.inria.fr/sympa/arc/mpfr/2016-12/msg00032.html)

    Set $rop to $op ** (-1 / $ui) rounded in the direction $rnd.
    This function sets its $rop to the reciprocal of the $rop that
    is set by Rmpfr_rootn_ui (below) for identical arguments.

    May not correctly handle overflow or underflow.

   $inex = Rmpfr_cbrt($rop, $op, $rnd);
    Set $rop to the cubic root of $op, rounded in the direction $rnd.

   $inex = Rmpfr_root($rop, $op, $ui $rnd);
    Deprecated in mpfr-4.0.0 - use Rmpfr_rootn_ui with mpfr-4 and later.
    This function will croak with "deprecation" warning if Math::MPFR
    has been built against mpfr-4.x.x or later.
    Set $rop to the $ui'th root of $op, rounded in the direction
    $rnd.  Return 0 if the operation is exact, a non-zero value
    otherwise.

   $inex = Rmpfr_rootn_ui($rop, $op, $ui $rnd); # mpfr-4.0.0 and later
    Same as Rmpfr_root except that $rop is set to +0 (instead of -0)
    when $op is -0 and $ui is even.
    This function (and Rmpfr_cbrt) agree with the rootn function of
    the IEEE 754-2008 standard (Section 9.2).

   $inex = Rmpfr_pow_ui($rop, $op, $ui, $rnd);
   $inex = Rmpfr_pow_uj($rop, $op, $uj, $rnd);
   $inex = Rmpfr_pow_si($rop, $op, $si, $rnd);
   $inex = Rmpfr_pow_sj($rop, $op, $sj, $rnd);
   $inex = Rmpfr_pown($rop, $op, $sj, $rnd); # same as Rmpfr_pow_sj
   $inex = Rmpfr_ui_pow_ui($rop, $ui, $ui, $rnd);
   $inex = Rmpfr_ui_pow($rop, $ui,  $op,  $rnd);
   $inex = Rmpfr_pow   ($rop, $op1, $op2, $rnd);
   $inex = Rmpfr_pow_z ($rop, $op,  $z,   $rnd); # $z is a mpz object

   $inex = Rmpfr_pow_IV($rop, $op,  $IV,  $rnd); # $IV is $Config{ivtype}
    Set $rop to 2nd arg raised to 3rd arg, rounded to the direction
    $rnd with the precision of $rop.  Return zero if the result is
    exact, a positive value when the result is greater than 2nd arg
    to the power 3rd arg, and a negative value when it is smaller.
    See the MPFR documentation for documentation regarding special
    cases (ie when nan or signed inf/zero values are involved).

   $inex = Rmpfr_powr($rop, $op1, $op2, $rnd);
    Corresponds to the 'powr' function from IEEE 754:
    $rop = exp($op2 * log($op1)) rounded to the direction $rnd
    with the precision of $rop.

   $inex = Rmpfr_compound ($rop, $op1, $op2, $rnd); # New in 4.3.0
   $inex = Rmpfr_compound_si($rop, $op1, $si, $rnd); # New in 4.2.0
    $rop = ($op1 + 1) ** 3rd_arg, rounded according to $rnd, to the
    precision of $rop. However, there are special cases:
     $rop is set to NaN when $op1 < -1;
     $rop is set to 1 when $op1 is NaN and $op2 is 0;
     $rop is set to +Inf when $op1 is -1 and $op2 < 0;
     $rop is set to +0   when $op1 is -1 and $op2 > 0.
     The other special cases follow the 'Rmpfr_pow' rules on
     (1 + OP1, OP2).

   $inex = Rmpfr_neg($rop, $op, $rnd);
    Set $rop to -$op rounded in the direction $rnd. Just
    changes the sign if $rop and $op are the same variable.

   $inex = Rmpfr_abs($rop, $op, $rnd);
    Set $rop to the absolute value of $op, rounded in the direction
    $rnd. Return 0 if the result is exact, a positive value if $rop
    is larger than the absolute value of $op, and a negative value
    otherwise.

   $inex = Rmpfr_dim($rop, $op1, $op2, $rnd);
    Set $rop to the positive difference of $op1 and $op2, i.e.,
    $op1 - $op2 rounded in the direction $rnd if $op1 > $op2, and
    +0 otherwise. $rop is set to NaN when $op1 or $op2 is NaN.

   $inex = Rmpfr_mul_2exp($rop, $op, $ui, $rnd);
   $inex = Rmpfr_mul_2ui($rop, $op, $ui, $rnd);
   $inex = Rmpfr_mul_2si($rop, $op, $si, $rnd);
    Set $rop to 2nd arg times 2 raised to 3rd arg rounded to the
    direction $rnd. Just increases the exponent by 3rd arg when
    $rop and 2nd arg are identical. Return zero when $rop = 2nd
    arg, a positive value when $rop > 2nd arg, and a negative
    value when $rop < 2nd arg.  Note: The 'Rmpfr_mul_2exp' function
    is defined for compatibility reasons; you should use
    'Rmpfr_mul_2ui' (or 'Rmpfr_mul_2si') instead.

   $inex = Rmpfr_div_2exp($rop, $op, $ui, $rnd);
   $inex = Rmpfr_div_2ui($rop, $op, $ui, $rnd);
   $inex = Rmpfr_div_2si($rop, $op, $si, $rnd);
    Set $rop to 2nd arg divided by 2 raised to 3rd arg rounded to
    the direction $rnd. Just decreases the exponent by 3rd arg
    when $rop and 2nd arg are identical.  Return zero when
    $rop = 2nd arg, a positive value when $rop > 2nd arg, and a
    negative value when $rop < 2nd arg.  Note: The 'Rmpfr_div_2exp'
    function is defined for compatibility reasons; you should
    use 'Rmpfr_div_2ui' (or 'Rmpfr_div_2si') instead.

   ##########

   COMPARISON

   $si = Rmpfr_cmp($op1, $op2);
   $si = Rmpfr_cmpabs($op1, $op2);
   $si = Rmpfr_cmpabs_ui($op, $ui);  # requires mpfr-4.1.0 and later
   $si = Rmpfr_cmp_ui($op, $ui);
   $si = Rmpfr_cmp_si($op, $si);
   $si = Rmpfr_cmp_d($op, $double);
   $si = Rmpfr_cmp_ld($op, $ld); # long double
   $si = Rmpfr_cmp_float128($op, $f128); # __float128
   $si = Rmpfr_cmp_z($op, $z); # $z is a mpz object
   $si = Rmpfr_cmp_q($op, $q); # $q is a mpq object
   $si = Rmpfr_cmp_f($op, $f); # $f is a mpf object
   $si = Rmpfr_cmp_IV($op, $iv); # $iv is $Config{ivtype}
   $si = Rmpfr_cmp_NV($op, $nv); # $nv is $Config{nvtype}
   $si = Rmpfr_cmp_str($op, $str);
    Compare 1st and 2nd args. In the case of 'Rmpfr_cmpabs()' and
    'Rmpfr_cmpabs_ui' compare the absolute values of the 2 args.
    Return a positive value if 1st arg > 2nd arg, zero if
    1st arg = 2nd arg, and a negative value if 1st arg < 2nd arg.
    Both args are considered to their full own precision, which may
    differ. ($str will be compared at infinite precision.)
    In case 1st and 2nd args are of same sign but different,
    the absolute value returned is one plus the absolute difference
    of their exponents. If one of the operands is NaN (Not-a-Number),
    return zero and set the erange flag.

    NOTE:
         1) Rmpfr_cmp_IV() requires that the 2nd argument has its
         IOK flag set, and Rmpfr_cmp_NV() requires that the 2nd
         argument has its NOK flag set.
         Otherwise these functions croak.
         Suggestion: first check the status of the flag using
         IOK_flag($iv) or NOK_flag($nv),which return a non-zero
         value if and only if the flag in question is set.

         2) Rmpfr_cmp_IV handles both signed and unsigned IV args.

   $si = fr_cmp_q_rounded($op, $q, $rnd); # $q is a mpq object
    Convert $q to an mpfr object of current default precision,
    rounded in accordance with the value specified by $rnd.
    Then compare $op with this mpfr object, according to the rules
    specified for Rmpfr_cmp (above).

   $bool = Rmpfr_total_order_p($op1, $op2); # new with mpfr-4.1.0
    This function implements the totalOrder predicate from IEEE
    754-2008, where -NaN < -Inf < negative finite numbers < -0 < +0
    < positive finite numbers < +Inf < +NaN. It returns a non-zero
    value (true) when X is smaller than or equal to Y for this order
    relation, and zero (false) otherwise.
    Contrary to 'Rmpfr_cmp($x, $y)', which returns a ternary value,
    'Rmpfr_total_order_p' returns a binary value (zero or non-zero).
    In particular, 'Rmpfr_total_order_p($x, $x)' returns true,
    'Rmpfr_total_order_p(-0, +0)' returns true and
    'Rmpfr_total_order_p(+0, -0)' returns false.
    The sign bit of NaN also matters.
    This function falls back to our own implementation if the mpfr
    version is older than 4.1.0 (because, in that case,
    mpfr_total_order_p is unavailable).

   $si = Rmpfr_cmp_ui_2exp($op, $ui, $si);
   $si = Rmpfr_cmp_si_2exp($op, $si, $si);
    Compare 1st arg and 2nd arg multiplied by two to the power
    3rd arg.

   $bool = Rmpfr_eq($op1, $op2, $ui);
    The mpfr library function mpfr_eq may change in future
    releases of the mpfr library (post 2.4.0). If that happens,
    the change will also be reflected in Rmpfr_eq.
    Return non-zero if the first $ui bits of $op1 and $op2 are
    equal, zero otherwise.  I.e., tests if $op1 and $op2 are
    approximately equal.

   $bool = Rmpfr_nan_p($op);
    Return non-zero if $op is Not-a-Number (NaN), zero otherwise.

   $bool = Rmpfr_inf_p($op);
    Return non-zero if $op is plus or minus infinity, zero otherwise.

   $bool = Rmpfr_number_p($op);
    Return non-zero if $op is an ordinary number, i.e. neither
    Not-a-Number nor plus or minus infinity.

   $bool = Rmpfr_zero_p($op);
    Return non-zero if $op is zero. Else return 0.

   $bool = Rmpfr_regular_p($op); # mpfr-3.0.0 and later only
    Return non-zero if $op is a regular number (i.e. neither NaN,
    nor an infinity nor zero). Return zero otherwise.

   Rmpfr_reldiff($rop, $op1, $op2, $rnd);
    Compute the relative difference between $op1 and $op2 and
    store the result in $rop.  This function does not guarantee
    the exact rounding on the relative difference; it just
    computes abs($op1-$op2)/$op1, using the rounding mode
    $rnd for all operations.

   $si = Rmpfr_sgn($op);
    Return a positive value if op > 0, zero if $op = 0, and a
    negative value if $op < 0.  Its result is not specified
    when $op is NaN (Not-a-Number).

   $bool = Rmpfr_greater_p($op1, $op2);
    Return non-zero if $op1 > $op2, zero otherwise.

   $bool = Rmpfr_greaterequal_p($op1, $op2);
    Return non-zero if $op1 >= $op2, zero otherwise.

   $bool = Rmpfr_less_p($op1, $op2);
    Return non-zero if $op1 < $op2, zero otherwise.

   $bool = Rmpfr_lessequal_p($op1, $op2);
    Return non-zero if $op1 <= $op2, zero otherwise.

   $bool = Rmpfr_lessgreater_p($op1, $op2);
    Return non-zero if $op1 < $op2 or $op1 > $op2 (i.e. neither
    $op1, nor $op2 is NaN, and $op1 <> $op2), zero otherwise
    (i.e. $op1 and/or $op2 are NaN, or $op1 = $op2).

   $bool = Rmpfr_equal_p($op1, $op2);
    Return non-zero if $op1 = $op2, zero otherwise
    (i.e. $op1 and/or $op2 are NaN, or $op1 <> $op2).

   $bool = Rmpfr_unordered_p($op1, $op2);
     Return non-zero if $op1 or $op2 is a NaN
     (i.e. they cannot be compared), zero otherwise.

   #######

   SPECIAL

   $rop = log_2 ($op);
   $rop = log_10($op);
    Return log2 of $op (resp. log10 of $op), set to default
    precision and using default rounding mode.
    These are the functions that log2 and log10 overloading would
    call if log2 and log10 overloading was available.

   $inex = Rmpfr_log($rop, $op, $rnd);
   $inex = Rmpfr_log_ui($rop, $ui, $rnd); # mpfr-4.0.0 & later only
   $inex = Rmpfr_log2($rop, $op, $rnd);
   $inex = Rmpfr_log10($rop, $op, $rnd);
    Set $rop to the natural logarithm of $op, the natural
    logarithm  of $ui, log2($op) or log10($op), respectively,
    rounded in the direction $rnd.

   $inex = Rmpfr_exp($rop, $op, $rnd);
   $inex = Rmpfr_exp2($rop, $op, $rnd);
   $inex = Rmpfr_exp10($rop, $op, $rnd);
    Set rop to the exponential of op, to 2 power of op or to
    10 power of op, respectively, rounded in the direction rnd.

   $rop = sind($op); # Value of $op is in degrees (not radians)
   $rop = cosd($op); # Value of $op is in degrees (not radians)

    Return (respectively) sin() and cos() of $op, where the
    value of $op is expressed in degrees. The return value is
    calculated using default precision and default rounding mode.
    These are essentially the same as the overloaded sin and
    cos functions except that the given argument is in degrees.

   $rop = tand($op);    # $op is in degrees (not radians)
   $rop = tangent($op); # $op is in radians
    Return tan($op) calculated with default precision and
    default rounding mode.

   $inex = Rmpfr_sin($rop $op, $rnd);
   $inex = Rmpfr_cos($rop, $op, $rnd);
   $inex = Rmpfr_tan($rop, $op, $rnd);
    Set $rop to the sine/cosine/tangent respectively of $op,
    rounded to the direction $rnd with the precision of $rop.
    Return 0 if the result is exact (this occurs in fact only
    when $op is 0 i.e. the sine is 0, the cosine is 1, and the
    tangent is 0). Return a negative value if the result is less
    than the actual value. Return a positive result if the
    return is greater than the actual value.

   $si = Rmpfr_sin_cos($rop1, $rop2, $op, $rnd);
    Set simultaneously $rop1 to the sine of $op and
    $rop2 to the cosine of $op, rounded to the direction $rnd
    with their corresponding precisions.  Return 0 if both
    results are exact.

   $inex = Rmpfr_cosu($rop, $op, $ui, $rnd); # mpfr-4.2.0 and later only
   $inex = Rmpfr_sinu($rop, $op, $ui, $rnd); # mpfr-4.2.0 and later only
   $inex = Rmpfr_tanu($rop, $op, $ui, $rnd); # mpfr-4.2.0 and later only
    Set $rop to the cosine (resp. sine and tangent) of $op multiplied by
    2*Pi and divided by $ui.  For example, if $ui equals 360, one gets
    the cosine (resp. sine and tangent) for $op in degrees.  For
    'Rmpfr_cosu', when $op multiplied by 2 and divided by $ui is a
    half-integer, the result is +0, following IEEE 754-2019 (cosPi), so
    that the function is even.  For 'Rmpfr_sinu', when $op multiplied by
    2 and divided by $ui is an integer, the result is zero with the same
    sign as $op, following IEEE 754-2019 (sinPi), so that the function
    is odd.  Similarly, the function 'Rmpfr_tanu' follows IEEE 754-2019
    (tanPi).
    Rmpfr_cosu/sinu/tanu   ($rop, $op, $ui,    $rnd) is equivalent to
    Rmpfr_cospi/sinpi/tanpi($rop, ($op/$ui)/2, $rnd) below.

   $inex = Rmpfr_acosu($rop, $op, $ui, $rnd); # mpfr-4.2.0 and later only
   $inex = Rmpfr_asinu($rop, $op, $ui, $rnd); # mpfr-4.2.0 and later only
   $inex = Rmpfr_atanu($rop, $op, $ui, $rnd); # mpfr-4.2.0 and later only
    Set $rop to X multiplied by $ui and divided by 2*Pi, where X is the
    arc-cosine (resp. arc-sine and arc-tangent) of $op.  For example,
    if $ui equals 360, mpfr_acosu yields the arc-cosine in degrees.

   $inex = Rmpfr_cospi($rop, $op, $rnd); # mpfr-4.2.0 and later only
   $inex = Rmpfr_sinpi($rop, $op, $rnd); # mpfr-4.2.0 and later only
   $inex = Rmpfr_tanpi($rop, $op, $rnd); # mpfr-4.2.0 and later only
    Set $rop to the cosine (resp. sine and tangent) of $op multiplied
    by Pi.  See the description of 'Rmpfr_sinu', 'Rmpfr_cosu' and
    'Rmpfr_tanu' for special values.
    Rmpfr_cospi/sinpi/tanpi($rop, $op, $rnd) is equivalent to
    Rmpfr_cosu/sinu/tanu   ($rop, $op, 2, $rnd) above.

   $inex = Rmpfr_acospi($rop, $op, $rnd); # mpfr-4.2.0 and later only
   $inex = Rmpfr_asinpi($rop, $op, $rnd); # mpfr-4.2.0 and later only
   $inex = Rmpfr_atanpi($rop, $op, $rnd); # mpfr-4.2.0 and later only
    $rop = acos($op)/Pi, resp. asin($op)/Pi and atan($op)/Pi.

   $inex = Rmpfr_sinh_cosh($rop1, $rop2, $op, $rnd);
    Set simultaneously $rop1 to the hyperbolic sine of $op and
    $rop2 to the hyperbolic cosine of $op, rounded in the direction
    $rnd with the corresponding precision of $rop1 and $rop2 which
    must be different variables. Return 0 if both results are
    exact.

   $inex = Rmpfr_acos($rop, $op, $rnd);
   $inex = Rmpfr_asin($rop, $op, $rnd);
   $inex = Rmpfr_atan($rop, $op, $rnd);
    Set $rop to the arc-cosine, arc-sine or arc-tangent of $op,
    rounded to the direction $rnd with the precision of $rop.
    Return 0 if the result is exact. Return a negative value if
    the result is less than the actual value. Return a positive
    result if the return is greater than the actual value.

   $inex = Rmpfr_atan2($rop, $op1, $op2, $rnd);
    Set $rop to the tangent of $op1/$op2, rounded to the
    direction $rnd with the precision of $rop.
    Return 0 if the result is exact. Return a negative value if
    the result is less than the actual value. Return a positive
    result if the return is greater than the actual value.
    See the MPFR documentation for details regarding special cases.

   $inex = Rmpfr_atan2u($rop, $op1, $op2, $ui, $rnd);
    Same as taking the Rmpfr_atan2() result and multiplying it
    by $ui/(2*Pi).

   $inex = Rmpfr_atan2pi($rop, $op1, $op2, $rnd);
    Same as Rmpfr_atan2u() with $ui = 2.

   $inex = Rmpfr_cosh($rop, $op, $rnd);
   $inex = Rmpfr_sinh($rop, $op, $rnd);
   $inex = Rmpfr_tanh($rop, $op, $rnd);
    Set $rop to the hyperbolic cosine/hyperbolic sine/hyperbolic
    tangent respectively of $op, rounded to the direction $rnd
    with the precision of $rop.  Return 0 if the result is exact
    (this occurs in fact only when $op is 0 i.e. the result is 1).
    Return a negative value if the result is less than the actual
    value. Return a positive result if the return is greater than
    the actual value.

   $inex = Rmpfr_acosh($rop, $op, $rnd);
   $inex = Rmpfr_asinh($rop, $op, $rnd);
   $inex = Rmpfr_atanh($rop, $op, $rnd);
    Set $rop to the inverse hyperbolic cosine, sine or tangent
    of $op, rounded to the direction $rnd with the precision of
    $rop.  Return 0 if the result is exact.

   $inex = Rmpfr_sec ($rop, $op, $rnd);
   $inex = Rmpfr_csc ($rop, $op, $rnd);
   $inex = Rmpfr_cot ($rop, $op, $rnd);
    Set $rop to the secant of $op, cosecant of $op,
    cotangent of $op, rounded in the direction RND. Return 0
    if the result is exact. Return a negative value if the
    result is less than the actual value. Return a positive
    result if the return is greater than the actual value.

   $inex = Rmpfr_sech ($rop, $op, $rnd);
   $inex = Rmpfr_csch ($rop, $op, $rnd);
   $inex = Rmpfr_coth ($rop, $op, $rnd);
    Set $rop to the hyperbolic secant of $op, cosecant of $op,
    cotangent of $op, rounded in the direction RND. Return 0
    if the result is exact. Return a negative value if the
    result is less than the actual value. Return a positive
    result if the return is greater than the actual value.

   $inex = Rmpfr_fac_ui($rop, $ui, $rnd);
    Set $rop to the factorial of $ui, rounded to the direction
    $rnd with the precision of $rop.

   $inex = Rmpfr_log1p  ($rop, $op, $rnd);
   $inex = Rmpfr_log2p1 ($rop, $op, $rnd);
   $inex = Rmpfr_log10p1($rop, $op, $rnd);
    In Rmpfr_log1p   set $rop = log(  $op + 1).
    In Rmpfr_log2p1  set $rop = log2( $op + 1).
    In Rmpfr_log10p1 set $rop = log10($op + 1).
    In all three cases, round the result in the
    direction $rnd to the precision of $rop.

   $inex = Rmpfr_expm1  ($rop, $op, $rnd);
   $inex = Rmpfr_exp2m1 ($rop, $op, $rnd);
   $inex = Rmpfr_exp10m1($rop, $op, $rnd);
    In Rmpfr_expm1, set $rop to the exponential of $op followed
    by a subtraction of 1. $rop = (e  ** $op) - 1.
    In Rmpfr_exp2p1,  set $rop = (2  ** $op) - 1.
    In Rmpfr_exp10p1, set $rop = (10 ** $op) - 1.
    For all three, the result is rounded to the direction $rnd
    with the precision of $rop.

   $inex = Rmpfr_fma($rop, $op1, $op2, $op3, $rnd);
    Set $rop to $op1 * $op2 + $op3, rounded to the direction $rnd.

   $inex = Rmpfr_fmma($rop, $op1, $op2, $op3, $op4, $rnd);
    NOTE: Needs mpfr-4.0.0 or later
    Set $rop to $op1 * $op2 + $op3 * $op4, rounded to the
    direction $rnd.

   $inex = Rmpfr_fms($rop, $op1, $op2, $op3, $rnd);
    Set $rop to $op1 * $op2 - $op3, rounded to the direction $rnd.

   $inex = Rmpfr_fmms($rop, $op1, $op2, $op3, $op4, $rnd);
    NOTE: Needs mpfr-4.0.0 or later
    Set $rop to $op1 * $op2 - $op3 * $op4, rounded to the
    direction $rnd.

   $inex = Rmpfr_agm($rop, $op1, $op2, $rnd);
    Set $rop to the arithmetic-geometric mean of $op1 and $op2,
    rounded to the direction $rnd with the precision of $rop.
    Return zero if $rop is exact, a positive value if $rop is
    larger than the exact value, or a negative value if $rop
    is less than the exact value.

   $inex = Rmpfr_hypot ($rop, $op1, $op2, $rnd);
    Set $rop to the Euclidean norm of $op1 and $op2, i.e. the
    square root of the sum of the squares of $op1 and $op2,
    rounded in the direction $rnd. Special values are currently
    handled as described in Section F.9.4.3 of the ISO C99
    standard, for the hypot function (note this may change in
    future versions): If $op1 or $op2 is an infinity, then plus
    infinity is returned in $rop, even if the other number is
    NaN.

   $inex = Rmpfr_ai($rop, $op, $rnd); # mpfr-3.0.0 and later only
    Set $rop to the value of the Airy function Ai on $op,
    rounded in the direction $rnd.  When $op is NaN, $rop is
    always set to NaN. When $op is +Inf or -Inf, $rop is +0.
    The current implementation is not intended to be used with
    large arguments.  It works with $op typically smaller than
    500. For larger arguments, other methods should be used and
    will be implemented soon.

   $inex = Rmpfr_const_log2($rop, $rnd);
    Set $rop to the logarithm of 2 rounded to the direction
    $rnd with the precision of $rop. This function stores the
    computed value to avoid another calculation if a lower or
    equal precision is requested.
    Return zero if $rop is exact, a positive value if $rop is
    larger than the exact value, or a negative value if $rop
    is less than the exact value.

   $inex = Rmpfr_const_pi($rop, $rnd);
    Set $rop to the value of Pi rounded to the direction $rnd
    with the precision of $rop. This function uses the Borwein,
    Borwein, Plouffe formula which directly gives the expansion
    of Pi in base 16.
    Return zero if $rop is exact, a positive value if $rop is
    larger than the exact value, or a negative value if $rop
    is less than the exact value.

   $inex = Rmpfr_const_euler($rop, $rnd);
    Set $rop to the value of Euler's constant 0.577...  rounded
    to the direction $rnd with the precision of $rop.
    Return zero if $rop is exact, a positive value if $rop is
    larger than the exact value, or a negative value if $rop
    is less than the exact value.

   inex = Rmpfr_const_catalan($rop, $rnd);
    Set $rop to the value of Catalan's constant 0.915...
    rounded to the direction $rnd with the precision of $rop.
    Return zero if $rop is exact, a positive value if $rop is
    larger than the exact value, or a negative value if $rop
    is less than the exact value.

   Rmpfr_free_cache();
    Free the cache used by the functions computing constants if
    needed (currently 'mpfr_const_log2', 'mpfr_const_pi' and
    'mpfr_const_euler').

   Rmpfr_free_cache2($ui);        # mpfr-4.0.0 and later only
    Free various caches and pools used by MPFR internally, as
    specified by $ui, which is a set of flags:
     a) those local to the current thread if flag
        MPFR_FREE_LOCAL_CACHE is set;
     b) those shared by all threads if flag
        MPFR_FREE_GLOBAL_CACHE is set.

    The other bits of $ui are currently ignored and are reserved for
    future use; they should be zero.
    Note:
    Rmpfr_free_cache2(MPFR_FREE_LOCAL_CACHE|MPFR_FREE_GLOBAL_CACHE)
    is currently equivalent to mpfr_free_cache().

   Rmpfr_free_pool()             # mpfr-4.0.0 and later only
    Free the pools used by mpfr internally.
    Note:
    This function is automatically called after the thread-local
    caches are freed (with mpfr_free_cache or mpfr_free_cache2).

   $inex = Rmpfr_beta($rop, $op1, $op2, $rnd); # mpfr-4.0.0 &
                                             # later only
    Set $rop to the beta function at $op1, $op2, rounded
    according to $rnd.

   $inex = Rmpfr_gamma($rop, $op, $rnd);
   $inex = Rmpfr_lngamma($rop, $op, $rnd);
    Set $rop to the value of the Gamma function on $op
   (and, respectively, its natural logarithm) rounded
    to the direction $rnd. Return zero if $rop is exact, a
    positive value if $rop is larger than the exact value, or a
    negative value if $rop is less than the exact value.
    'Rmpfr_gamma' sets $rop to NaN when $op is negative.

   $inex = Rmpfr_gamma_inc($rop, $op1, $op2, $rnd); # mpfr-4.0.0 &
                                                  # later only
    Set $rop to the value of the incomplete Gamma function on $op1
    and $op2, rounded in the direction $rnd.
    When $op2 is zero and $op1 is a negative value, $rop is set to
    NaN.
    Note: the current implementation is slow for large values of
          $rop and $op, in which case some internal overflow might
          also occur.

   ($signp, $si) = Rmpfr_lgamma ($rop, $op, $rnd);
    Set $rop to the value of the logarithm of the absolute value
    of the gamma function on $op, rounded in the direction $rnd.
    The sign (1 or -1) of gamma($op) is returned in $signp.
    When $op is an infinity or a non-positive integer, +Inf is
    returned. When $op is NaN, -Inf or a negative integer, $signp
    is undefined, and when $op is 0, $signp is the sign of the zero.

   $inex = Rmpfr_digamma($rop, $op, $rnd); # mpfr-3.0.0 and later only
    Set $rop to digammma($op), rounded according to $rnd.

   $inex = Rmpfr_trigamma ($rop, $op, $rnd); # mpfr-4.3.0 and later only
    Set $rop to trigammma($op), rounded according to $rnd.

   $inex = Rmpfr_zeta($rop, $op, $rnd);
   $inex = Rmpfr_zeta_ui($rop, $ul, $rnd);
    Set $rop to the value of the Riemann Zeta function on 2nd arg,
    rounded to the direction $rnd. Return zero if $rop is exact,
    a positive value if $rop is larger than the exact value, or
    a negative value if $rop is less than the exact value.

   $inex = Rmpfr_erf($rop, $op, $rnd);
    Set $rop to the value of the error function on $op,
    rounded to the direction $rnd. Return zero if $rop is exact,
    a positive value if $rop is larger than the exact value, or
    a negative value if $rop is less than the exact value.

   $inex = Rmpfr_erfc($rop, $op, $rnd);
    Set $rop to the complementary error function on $op,
    rounded to the direction $rnd. Return zero if $rop is exact,
    a positive value if $rop is larger than the exact value, or
    a negative value if $rop is less than the exact value.

   $inex = Rmpfr_j0 ($rop, $op, $rnd);
   $inex = Rmpfr_j1 ($rop, $op, $rnd);
   $inex = Rmpfr_jn ($rop, $si2, $op, $rnd);
    Set $rop to the value of the first order Bessel function of
    order 0, 1 and $si2 on $op, rounded in the direction $rnd.
    When $op is NaN, $rop is always set to NaN. When $op is plus
    or minus Infinity, $rop is set to +0. When $op is zero, and
    $si2 is not zero, $rop is +0 or -0 depending on the parity
    and sign of $si2, and the sign of $op.

   $inex = Rmpfr_y0 ($rop, $op, $rnd);
   $inex = Rmpfr_y1 ($rop, $op, $rnd);
   $inex = Rmpfr_yn ($rop, $si2, $op, $rnd);
     Set $rop to the value of the second order Bessel function of
     order 0, 1 and $si2 on $op, rounded in the direction $rnd.
     When $op is NaN or negative, $rop is always set to NaN.
     When $op is +Inf, $rop is +0. When $op is zero, $rop is +Inf
     or -Inf depending on the parity and sign of $si2.

   $inex = Rmpfr_eint ($rop, $op, $rnd)
     Set $rop to the exponential integral of $op, rounded in the
     direction $rnd. See the MPFR documentation for details.
     As of mpfr-4.0.0 Rmpfr_eint() returns the value of the
     E1/eint1 function for negative input. (With previous versions
     of mpfr NaN was returned for negative argument.)

   $inex = Rmpfr_li2 ($rop, $op, $rnd);
    Set $rop to real part of the dilogarithm of $op, rounded in the
    direction $rnd. The dilogarithm function is defined here as
    the integral of -log(1-t)/t from 0 to x.

   $inex = Rmpfr_dot ($rop, \@op1, \@op2, $ui, $rnd); # mpfr-4.1.0 &
                                                    # later only
    Set $rop to the dot product of elements of @op1 by those of
    @op2, whose common size is $ui (== scalar @op1), correctly
    rounded in the direction $rnd.
    This function is experimental, and does not yet handle
    intermediate overflows and underflows.

   #############

   I-O FUNCTIONS

   $ui = Rmpfr_out_str([$prefix,] $op, $base, $digits, $round [, $suffix]);
    BEST TO USE TRmpfr_out_str INSTEAD
    Output $op to STDOUT, as a string of digits in base $base,
    rounded in direction $round.  $base may be in the range 2 to 62
    (or -36..-2, 2 .. 62 if Math::MPFR has been built against
    mpfr-4.1.0 or later).
    Print $digits significant digits exactly, or if $digits is 0,
    enough digits so that $op can be read back exactly
    (see Rmpfr_get_str). In addition to the significant
    digits, a decimal point at the right of the first digit and a
    trailing exponent in base 10, in the form 'eNNN', are printed
    If $base is greater than 10, '@' will be used instead of 'e'
    as exponent delimiter. The optional arguments, $prefix and
    $suffix, are strings that will be prepended/appended to the
    mpfr_out_str output. Return the number of bytes written (not
    counting those contained in $suffix and $prefix), or if an error
    occurred, return 0. (Note that none, one or both of $prefix and
    $suffix can be supplied.)

   $ui = TRmpfr_out_str([$prefix,] $stream, $base, $digits, $op, $round [, $suffix]);
    As for Rmpfr_out_str, except that there's the capability to print
    to somewhere other than STDOUT. Note that the order of the args
    is different (to match the order of the mpfr_out_str args).
    To print to STDERR:
       TRmpfr_out_str(*stderr, $base, $digits, $op, $round);
    To print to an open filehandle (let's call it $fh):
       TRmpfr_out_str(\*$fh, $base, $digits, $op, $round);

   $ui = Rmpfr_inp_str($rop, $base, $round);
    BEST TO USE TRmpfr_inp_str INSTEAD.
    Input a string in base $base from STDIN, rounded in
    direction $round, and put the read float in $rop.  The string
    is of the form 'M@N' or, if the base is 10 or less, alternatively
    'MeN' or 'MEN', or, if the base is 16, alternatively 'MpB' or
    'MPB'. 'M' is the mantissa in the specified base, 'N' is the
    exponent written in decimal for the specified base, and in base 16,
    'B' is the binary exponent written in decimal (i.e. it indicates
    the power of 2 by which the mantissa is to be scaled).
    The argument $base may be in the range 2 to 62.
    Special values can be read as follows (the case does not matter):
    '@NaN@', '@Inf@', '+@Inf@' and '-@Inf@', possibly followed by
    other characters; if the base is smaller or equal to 16, the
    following strings are accepted too: 'NaN', 'Inf', '+Inf' and
    '-Inf'.
    Return the number of bytes read, or if non-numeric characters were
    encountered in the input, return 0.
    If 0 is returned:
      1) the non-numeric flag (which was initialised to 0) will be
         incremented. You can query/clear/reset the value of the
         flag with (resp.) nnumflag()/clear_nnum()/set_nnum() - all
         of which are documented below;
      2) A warning will be emitted if $Math::MPFR::NNW is set to 1
        (default is 0).

   $ui = TRmpfr_inp_str($rop, $stream, $base, $round);
    As for Rmpfr_inp_str, except that there's the capability to read
    from somewhere other than STDIN.
    To read from STDIN:
       TRmpfr_inp_str($rop, *stdin, $base, $round);
    To read from an open filehandle (let's call it $fh):
       TRmpfr_inp_str($rop, \*$fh, $base,  $round);

   Rmpfr_dump($op);
    Output "$op\n" on stdout in base 2.
    As with 'Rmpfr_print_binary' the exponent is in base 10.

   $si = Rmpfr_fpif_export ($stream, $op); # Needs mpfr-4.0.0
   $si = Rmpfr_fpif_import ($op, $stream); # Needs mpfr-4.0.0
   $si = Rmpfr_fpif_export_mem ($buf, $bufsize, $op); # Needs mpfr-4.3.0
   $si = Rmpfr_fpif_import_mem ($op, $buf, $bufsize); # Needs mpfr-4.3.0
    Note: These function are experimental and their interface might
          change in future versions of mpfr.
    Export/import the number $op to/from the stream/string
    $stream/$buf in a floating-point interchange format. The
    import function fails if the precision (which is read from
    the stream/string) is greater than RMPFR_PREC_MAX.
    Return 0 if the export/import was successful.
    For the two *_mem functions, $buf is a perl variable (SV) that
    does not need to have been initialized. $bufsize needs to be
    sufficiently large to accommodate the output of the function.
    You can calculate the minimum $bufsize with:

      $size = Rmpfr_fpif_size($op);
      $bufsize = Rmpfr_fpif_size($op) + 1; # Include the terminating
                                           # NULL byte
      Or, simply call the functions as:
      $si = Rmpfr_fpif_export_mem($buf, Rmpfr_fpif_size($op)+1, $op);
      $si = Rmpfr_fpif_import_mem($rop, $buf, length($buf));

   $ui = Rmpfr_fpif_size($op);
    Return a satisfactory value for the size of the string buffer
    needed as 1st arg to Rmpfr_fpif_export_mem() above.

   ########################

   DISPLAYING INFS AND NANS

   Generally, these will be displayed as 'Inf', '-Inf' and 'NaN'.
   However, if you set $Math::MPFR::PERL_INFNAN to a TRUE value,
   then nvtoa($num) and numtoa($num) (which are documented below
   in 'MISCELLANEOUS') will display them in the same way that perl
   itself displays them.
   Note that nvtoa() and numtoa() expect a plain numeric perl
   scalar as their argument - not a Math::MPFR object.
   $Math::MPFR::PERL_INFNAN has the initial (default) value of 0.

   ##########

   EXCEPTIONS

   $inex = Rmpfr_subnormalize ($op, $si, $rnd);
    This function subnormalizes $op when subnormalization is appropriate.
    Otherwise $op remains unchanged.
    See the MPFR documentation for mpfr_subnormalize at:
    https://www.mpfr.org/mpfr-current/mpfr.html#index-mpfr_005fsubnormalize

   $rop = subnormalize_float32 ($val);
   $rop = subnormalize_float16 ($val);
   $rop = subnormalize_bfloat16($val);
   $rop = subnormalize_generic ($val, $emin, $emax, $prec);
    $val can be an IV/UV,PV, NV, Math::GMPf object, Math::GMPq
    object or Math::MPFR object.
    For "float32" (ie the single precision "float"):
     Returns a 24-bit precision Math::MPFR object containing the
     value held by $val, adjusted for either "float" subnormalization
     or infinitude when appropriate. This sub simply calls:
        subnormalize_generic($_[0], -148, 128, 24);
    For "float16":
     Returns an 11-bit precision Math::MPFR object containing the
     value held by $val, adjusted for either "_Float16" subnormalization
     or infinitude when appropriate. This sub simply calls:
        subnormalize_generic($_[0], -23, 16, 11);
    For "bfloat16:
     Returns an 8-bit precision Math::MPFR object containing the
     value held by $val, adjusted for either "__bf16" subnormalization
     or infinitude when appropriate. This sub simply calls:
        subnormalize_generic($_[0], -132, 128, 8);
    For "generic":
     Returns a $prec-bit precision Math::MPFR object containing the
     value held by $val, adjusted for either subnormalization or
     infinitude (when appropriate), and based upon the value of $prec
     and upon the exponent range specified by $emin and $emax.

   $si =  Rmpfr_get_emin();
   $si =  Rmpfr_get_emax();
    Return to $si the (current) smallest and largest exponents
    allowed for a floating-point variable.

   $si = Rmpfr_get_emin_min();
   $si = Rmpfr_get_emin_max();
   $si = Rmpfr_get_emax_min();
   $si = Rmpfr_get_emax_max();
    Return to $si the minimum and maximum of the smallest and largest
    exponents allowed for 'mpfr_set_emin' and 'mpfr_set_emax'. These
    values are implementation dependent

   $bool =  Rmpfr_set_emin($si);
   $bool =  Rmpfr_set_emax($si);
    Set the smallest and largest exponents allowed for a
    floating-point variable.  Return a non-zero value when $si is not
    in the range of exponents accepted by the implementation (in that
    case the smallest or largest exponent is not changed), and zero
    otherwise. If the user changes the exponent range, it is her/his
    responsibility to check that all current floating-point variables
    are in the new allowed range (for example using 'Rmpfr_check_range',
    otherwise the subsequent behaviour will be undefined, in the sense
    of the ISO C standard.

   $inex = Rmpfr_check_range($op, $si, $rnd);
    This function assumes that $op is the correctly rounded value of
    some real value X in the direction $rnd and some extended exponent
    range, and that $si is the corresponding ternary value. Thus $si
    is negative if $op is smaller than X, positive if $op is larger than
    X, and zero if $op equals X.
    This function modifies $op if needed to be in the current range of
    acceptable values. It generates an underflow or an overflow if the
    exponent of $op is outside the current allowed range; the value of
    $si may be used to avoid a double rounding. This function returns
    zero if the new value of $op equals the exact one X, a positive
    value if that new value is larger than X, and a negative value if
    it is smaller than X. Note that unlike most functions, the new
    result $op is compared to the (unknown) exact one X, not the input
    value $op, i.e., the ternary value is propagated.

    Note: If $op is an infinity and $inex is different from zero (i.e.,
          if the rounded result is an inexact infinity), then the
          overflow flag is set.

   Rmpfr_set_underflow();
   Rmpfr_set_overflow();
   Rmpfr_set_nanflag();
   Rmpfr_set_inexflag();
   Rmpfr_set_erangeflag();
   Rmpfr_set_divby0();     # mpfr-3.1.0 and later only
   Rmpfr_clear_underflow();
   Rmpfr_clear_overflow();
   Rmpfr_clear_nanflag();
   Rmpfr_clear_inexflag();
   Rmpfr_clear_erangeflag();
   Rmpfr_clear_divby0();   # mpfr-3.1.0 and later only
    Set/clear the underflow, overflow, invalid, inexact, erange and
    divide-by-zero flags.

   Rmpfr_clear_flags();
    Clear all global flags (underflow, overflow, inexact, invalid,
    erange and divide-by-zero).

   $bool = Rmpfr_underflow_p();
   $bool = Rmpfr_overflow_p();
   $bool = Rmpfr_nanflag_p();
   $bool = Rmpfr_inexflag_p();
   $bool = Rmpfr_erangeflag_p();
   $bool = Rmpfr_divby0_p();   # mpfr-3.1.0 and later only
    Return the corresponding (underflow, overflow, invalid, inexact,
    erange, divide-by-zero) flag, which is non-zero if the flag is set.

   Rmpfr_flags_clear($mask);            # needs mpfr-4.0.0 or later
   Rmpfr_flags_set($mask);              # needs mpfr-4.0.0 or later
   $mask2 = Rmpfr_flags_test($mask);    # needs mpfr-4.0.0 or later
   $mask  = Rmpfr_flags_save();         # needs mpfr-4.0.0 or later
   Rmpfr_flags_restore($mask1, $mask2); # needs mpfr-4.0.0 or later
    $mask is an integer value resulting from OR'ing (or adding) any of
    the following constants together:
     MPFR_FLAGS_UNDERFLOW
     MPFR_FLAGS_OVERFLOW
     MPFR_FLAGS_NAN
     MPFR_FLAGS_INEXACT
     MPFR_FLAGS_ERANGE
     MPFR_FLAGS_DIVBY0
     MPFR_FLAGS_ALL
    MPFR_FLAGS_ALL is the same as all of those constants OR'ed (added)
    together. Examples:

    Clear the divby0 and nan flags, without affecting the status of
    any other flags:
     Rmpfr_flags_clear(MPFR_FLAGS_DIVBY0|MPFR_FLAGS_NAN);

    Set the underflow and erange flags, without affecting the status of
    any other flags:
     Rmpfr_flags_set(MPFR_FLAGS_UNDERFLOW|MPFR_FLAGS_ERANGE);

    Test the status of specific flags, ignoring all other flags. This
    particular example will set $mask to the value of MPFR_FLAGS_NAN
    if the nan flag is set - else $mask will be set to zero:
     $mask = Rmpfr_flags_test(MPFR_FLAGS_UNDERFLOW);

    Return all flags:
     $mask = Rmpfr_flags_save();
    Equivalently, this can be done with:
     $mask = Rmpfr_flags_test(MPFR_FLAGS_ALL);

    Set flags specified in $mask2 to the state specified in $mask1,
    For this example, the overflow flag will be set && the nan flag
    will be cleared. The underflow flag will remain untouched.
     $mask1 = MPFR_FLAGS_UNDERFLOW | MPFR_FLAGS_OVERFLOW;
     $mask2 = MPFR_FLAGS_OVERFLOW  | MPFR_FLAGS_NAN;
     Rmpfr_flags_restore($mask1, $mask2);

   #############

   MISCELLANEOUS

   $rop = nv2mpfr($sv);
    Return a new Math::MMPFR object whose value is the same as that
    held by $sv, with the same precision as that of $Config{nvtype}.

   $str = doubletoa($double [, $x]); # Available only when
                                 # $Config{nvsize} == 8.
                                 # Else use nvtoa().
    Sets $str to the value of $double.
    $str will appear in standard decimal format such that the
    condition ($str == $double) is true.
    The grisu3 algorithm used by this function, whilst very quick,
    will fail for about 0.5% of values. When this happens doubletoa
    will (by default) fall back to using nvtoa() - which is slower,
    but reliable.
    Alternatively, providing a second argument to doubletoa (any
    scalar will do) will ensure that it falls back to returning
    sprintf("%.17g", $double).This will be an accurate return, and
    it will be quicker than the nvtoa() fallback, but it often
    provides more digits than are necessary.
    Whenever doubletoa reverts to a fallback routine,
    $Math::MPFR::doubletoa_fallback (which is initially set to 0)
    will be incremented. This feature can be disabled by providing
    the FB=0 argument to the 'perl Makefile.PL' step of the
    Math::MPFR build.

   $str = nvtoa($NV); # Available irrespective of $Config{nvsize}
                      # and $Config{nvtype}
    Sets $str to the value of $NV.
    $str will appear in standard decimal format, containing the
    *minimum* number of digits such that the condition ($str == $NV)
    is true.
    NOTE 1: Except for perls whose nvtype is __float128:
             1) perl versions prior to 5.30.0 are buggy in their
                assignment of values to the NV;
             2) perl versions from 5.30.0 on that don't define
                $Config{d_strtod} (or respectively $Config{d_strtold}
                for -Duselongdouble builds) are also buggy in their
                assignment of values to the NV.
            The nvtoa() function looks only at the value that was
            passed to it - which, with such buggy perls, may differ
            from the intended value by a few ULPs.
            On these buggy perls, the bug can be avoided by assigning
            with atonv() - which requires mpfr-3.1.6 or later.
    NOTE 2: Be wary of values assigned by perl to double-double NVs,
            as such assignments may also be buggy, irrespective of
            the perl version.
            Again, with these perls, assign using atonv() - which
            requires mpfr-3.1.6 or later.
            With double-double NVs, nvtoa() currently requires
            mpfr-4.0.0 or later.

   $str = mpfrtoa($op [, $uv]); # $uv is optional.
    As for nvtoa(), except that mpfrtoa() instead takes a Math::MPFR
    object as its argument.
    Sets $str to the value of $op.
    This achieved by calling _mpfrtoa($op, 0).
    $str will appear in standard decimal format, containing the
    *minimum* number of significant digits such that the condition
    ($str == $op) is true whenever the current default precision
    equals the precision of $op.
    (The overloaded '==' operator evaluates $str according to the
    current default precision, so it can be that $str != $op when
    and only when the default precision != the precision of $op.)

    The second (optional) arg became available with Math-MPFR-4.24 and
    it can alter the behaviour of mpfrtoa when the value of $uv is
    greater than the precision of $op - which is useful in respect
    to subnormalization. However, if subnormal values are required
    use mpfrtoa_subn (documented below) instead of mpfrtoa.

    I have also used a 2nd argument arcanely in Math:FakeDD::dd_repro,
    as that seems to work. But that 2nd arg will be removed when/if I
    can work out how to implement that removal. (Might take a while.)

   $str = mpfrtoa_subn($op, $bits, $emin, $emax);
    The mpfr library does not automatically perform subnormalization.
    Hence, for a given subnormal $nv, nvtoa($nv) will often differ
    from mpfrtoa($op), even though $op == $nv.
    This function achieves its result by passing the appropriate
    first and second arguments to the _mpfrtoa XSub.
    It also works correctly with normal NV values.

    Some examples for those perls whose $Config{nvsize} is 8:

    use Math::MPFR qw(:mpfr);
    Rmpfr_set_default_prec(53); # Required precision 8-byte NVs.

     $nv = 2 ** -1070;
     $op = Math::MPFR->new($nv);
     @args = (53, -1073, 1024);
     print "ok\n" if $nv == $op;             # ok
     print nvtoa  ($nv), "\n";               # 8e-323
     print mpfrtoa($op), "\n";               # 7.905050333459945e-323
     print mpfrtoa_subn($op, @args), "\n\n"; # 8e-323

     # Any value with an exponent < -1073 will be zero:
     $op = Math::MPFR->new(2) ** -1075;      # Exponent is -1074
     $nv = Rmpfr_get_NV($op, MPFR_RNDN);
     print nvtoa  ($nv), "\n";               # 0.0
     print mpfrtoa($op), "\n";               # 2.4703282292062327e-324
     print mpfrtoa_subn($op, @args), "\n\n"; # 0.0

     # Any value with an exponent > 1024 will be Inf:
     $op = Math::MPFR->new(2) ** 1024;       # Exponent is 1025
     $nv = Rmpfr_get_NV($op, MPFR_RNDN);
     print nvtoa  ($nv), "\n";               # Inf
     print mpfrtoa($op), "\n";               # 1.797693134862316e+308
     print mpfrtoa_subn($op, @args), "\n\n"; # Inf
     __END__

    For perls whose $Config{nvtype} is the 80-bit extended precision
    long double, the default precision would be set to 64 and @args
    to (64, -16444, 16384).

    For all other perls, the default precision would be set to 113,
    and @args set to (113, -16493, 16384).

   $str = anytoa($op); # $op precision must be 53 or 64 or 113.

      Note: It's probably now  better to use mpfrtoa_subn (above) as
            that sub also handles subnormals and Infs.

    For example, if you want to know what nvtoa(sqrt 3) would return
    on a perl whose nvtype is the 113-bit precision __float128 (or
    IEEE-754 128-bit long double) but you don't have access to such
    a perl, you can do:

      my $bits = 113;
      Rmpfr_set_default_prec($bits);
      $op = sqrt(Math::MPFR->new('3'));
      my $s = anytoa($op);
      print "$s\n"; # 1.7320508075688772935274463415058723

    Similarly, changing $bits to 53, or 64 would provide
    the same as nvtoa(sqrt 3) for (respectively) the 53-bit
    precision double nvtype  and the 64-bit extended precision long
    double nvtype.

    The value returned will be the same as returned by mpfrtoa($op)
    unless:

     1) $op holds a finite value that is of such magnitude that
        it will become (+ or -) Inf when converted to the
        specified nvtype;

     or

     2) $op holds a finite non-zero value that is so close to zero
        that the specified nvtype will either round it to zero or
        denormalize it;

   $mask = nvtoa_test($str, $arg [, $debug]);
    DEPRECATED - dragon_test (see below) is recommended instead.
    If $arg is a Math::MPFR object, then $str must be the string
    returned by mpfrtoa($arg). Else it must be the string returned
    by nvtoa($arg).
    Otherwise, nvtoa_test is essentially the same as dragon_test.
    If you want to back yourself to provide the appropriate $str/$arg
    combination, then please feel free to keep using nvtoa_test until
    such time as it is removed.

   $mask = dragon_test($arg [, $debug]);
    If $debug is provided and matches /debug/i, then some debug info is
    output during the running of this function.
    $arg can be either an IV or an NV or a Math::MPFR object.
    For an IV or NV we test the string returned by nvtoa($arg) for
    correctness.
    For a Math::MPFR object we test the string returned by mpfrtoa($arg)
    for correctness.
    In both cases we establish that the string will assign to $arg, and
    that the mantissa portion of the string also contains the minimum
    number of significant decimal digits required for that round trip to
    succeed.
    $mask is initially set to zero.
    If the string assigns to $arg (as it should) then $mask is set to 1.
    Also, we chop the least significant digit off the mantissa portion of
    the string, and add 2 to $mask if this chopped string assigns to a
    value less than $arg.
    Then we increment the least significant mantissa digit of this chopped
    string - and add 4 to $mask if this chopped-and-incremented string
    assigns to a value greater than $arg.
    Also, we check that the mantissa portion of $str contains no
    unwelcome trailing zeroes - and add 8 to $mask if this check passes.
    $mask is then returned. If all is correct, it's value will be 15.
    If the value of the returned $mask is not 15, then we can determine
    which part(s) of the test failed by examining $mask's 4 lowest bits.
    In the event of a failure, re-running the test with 'debug' will
    provide some clarifying info.

    For inf, nan, and single-digit mantissas, we do only the initial test
    and return 15 if that test has passed, or 0 if that test has failed.
    (The other 3 tests don't really apply to these cases.)

   $str = numtoa($sv);
    As for nvtoa() but prints out UVs and IVs in integer format.
    (If UV-precision is greater than NV-precision then nvtoa()
    output can lose precision as it prints out UVs and IVs in
    floating point format.)

   $double = atodouble($str); # Needs mpfr-3.1.6 or later
    Sets $double to the value of the double that's represented by
    the string $str.
    If $Config{nvtype} is double, it therefore returns the same
    value as atonv.
    See atonv() below.

   $NV = atonv($str); # Needs mpfr-3.1.6 or later
    Sets $NV to the NV value represented by the string $str.
    If $str expresses a base 2 value, begin it with '0b' or '0B'.
    If $str expresses a base 16 value, begin it with '0x' or '0X.
    If $str expresses a base 8 value then do not pass $str directly
    to atonv(). Instead do $NV = atonv(oct2bin($str));
    (See the oct2bin documentation immediately below.)
    For example:
      atonv('0x0.89p5'), atonv('0x0.112@2'), atonv('17.125'),
      atonv('0b0.10001001e5') and atonv(oct2bin('0.422p5')) all
      return 17.125.
    Any underscoeres included in the given argument will be treated
    as non-numeric (illegal) characters.

   $str2 = oct2num($str);
    Treats $str as an octal string, and returns the equivalent
    base 2 expression of that string, including the '0b'
    identifying prefix. This enables atonv() to handle octal values.
    The argument may (but does not need to) contain the 0/0o/0O
    identifying prefix. Use 'p' or 'P' to separate the mantissa
    from the exponent, and express the exponent as a base 10
    integer. The value will be the mantissa multiplied by 2 raised
    to the power of that base 10 integer. For example:
      '5p3' == 5 * (2 ** 3) == 40.
      oct2bin('-5p3') will return the string '-0b101p3'.

   $sv = atonum($str); # Needs mpfr-3.1.6 or later
    $str is treated as a decimal (base 10) value.
    Bases 2, 8, and 16 might be accommodated in the future.
    If $str numifies to an IV, return that IV.
    Else return the NV that is returned by atonv($str).

   $ret = decimalize($op [, $anything]); # 2nd (optional) arg
                                         # can be any scalar.
    If no second argument is provided, return an exact base 10
    string representation of the value held in $op.
    Else, instead return the number of decimal digits (not counting
    leading zeros) contained in the significand of that "exact base 10
    representation", as estimated by decimalize(). This value could be
    one greater than the actual number of those significand digits.
    If a second arg is supplied && $op is Inf or NaN or Zero, then
    the returned value will be zero.
    NOTE:
    https://www.exploringbinary.com/maximum-number-of-decimal-digits-in-binary-floating-point-numbers/
    explains that the maximum number of significant digits returned
    for a double precision value will be 767:
    1074 + 1 + floor(log10(((2**53)-1) / (2**1074))    = 767
    For the 80-bit extended precision long double:
    16445 + 1 + floor(log10(((2**64)-1) / (2**16445))  = 11514
    For IEEE-754 long double and _Float128:
    16494 + 1 + floor(log10(((2**113)-1) / (2**16494)) = 11563

   $bool = check_exact_decimal($str, $op);
    Can be used to verify the string returned by decimalize().
    Return 1 if $str is an exact decimal representation of the value
    held in $op.
    Else return 0.

   $MPFR_version = Rmpfr_get_version();
    Returns the version of the MPFR library (eg 4.0.2) being used by
    Math::MPFR.

   $GMP_version = Math::MPFR::gmp_v();
    Returns the version of the gmp library (eg. 4.1.3) being used by
    the mpfr library that's being used by Math::MPFR.
    The function is not exportable.

   $ui = MPFR_VERSION;
    An integer whose value is dependent upon the 'major', 'minor' and
    'patchlevel' values of the MPFR library against which Math::MPFR
    was built.
    This value is from the mpfr.h that was in use when the compilation
    of Math::MPFR took place.

   $ui = MPFR_VERSION_MAJOR;
    The 'x' in the 'x.y.z' of the MPFR library version.
    This value is from the mpfr.h that was in use when the compilation
    of Math::MPFR took place.

   $ui = MPFR_VERSION_MINOR;
    The 'y' in the 'x.y.z' of the MPFR library version.
    This value is from the mpfr.h that was in use when the compilation
    of Math::MPFR took place.

   $ui = MPFR_VERSION_PATCHLEVEL;
    The 'z' in the 'x.y.z' of the MPFR library version.
    This value is from the mpfr.h that was in use when the compilation
    of Math::MPFR took place.

   $string = MPFR_VERSION_STRING;
    $string is set to the version of the MPFR library (eg 2.1.0)
    against which Math::MPFR was built.
    This value is from the mpfr.h that was in use when the compilation
    of Math::MPFR took place.

   $ui = MPFR_VERSION_NUM($major, $minor, $patchlevel);
    Returns the value for MPFR_VERSION for "MPFR-$major.$minor.$patchlevel".

   $str = Rmpfr_get_patches();
    Return a string containing the ids of the patches applied to the
    MPFR library (contents of the 'PATCHES' file), separated by spaces.
    Note: If the program has been compiled with an older MPFR version and
    is dynamically linked with a new MPFR library version, the ids of the
    patches applied to the old (compile-time) MPFR version are not
    available (however this information should not have much interest
    in general).

   $bool = Rmpfr_buildopt_tls_p(); # mpfr-3.0.0 and later only
    Return a non-zero value if mpfr was compiled as thread safe using
    compiler-level Thread Local Storage (that is mpfr was built with
    the '--enable-thread-safe' configure option), else return zero.

   $bool = Rmpfr_buildopt_decimal_p(); # mpfr-3.0.0 and later only
    Return a non-zero value if mpfr was compiled with decimal float
    support (that is mpfr was built with the '--enable-decimal-float'
    configure option), return zero otherwise.

   $bool = Rmpfr_buildopt_float128_p(); # mpfr-4.0.0 and later only
    Return a non-zero value if mpfr was compiled with __float128
    support (that is mpfr was built with the '--enable-decimal-float'
    configure option), return zero otherwise.

   $bool = Rmpfr_buildopt_gmpinternals_p(); # mpfr-3.1.0 and later only
    Return a non-zero value if mpfr was compiled with gmp internals
    (that is, mpfr was built with either '--with-gmp-build' or
    '--enable-gmp-internals' configure option), return zero otherwise.

   $bool = Rmpfr_buildopt_sharedcache_p(); # mpfr-4.0.0 and later only
    Return a non-zero value if MPFR was compiled so that all threads
    share the same cache for the one MPFR constant, like `mpfr_const_pi'
    or `mpfr_const_log2' (that is, MPFR was built with the
    `--enable-shared-cache' configure option), return zero otherwise.

   $str = Rmpfr_buildopt_tune_case();  # mpfr-3.1.0 and later only
    Return a string saying which thresholds file has been used at
    compile time.  This file is normally selected from the processor
    type. If "make tune" has been used, then it will return
    "src/mparam.h". Otherwise it will say which official mparam.h file
    has been used.

   $inex = Rmpfr_rint($rop, $op, $rnd);
   $inex = Rmpfr_ceil($rop, $op);
   $inex = Rmpfr_floor($rop, $op);
   $inex = Rmpfr_round($rop, $op);
   $inex = Rmpfr_roundeven($rop, $op); # mpfr-4.0.0 and later only
   $inex = Rmpfr_trunc($rop, $op);
    Set $rop to $op rounded to an integer. 'Rmpfr_ceil' rounds to the
    next higher representable integer, 'Rmpfr_floor' to the next lower,
    'Rmpfr_round' to the nearest representable integer, rounding
    halfway cases away from zero, 'Rmpfr_roundeven' to the nearest
    representable integer, rounding halfway cases with the even-
    rounding rule and 'Rmpfr_trunc' to the representable integer
    towards zero. 'Rmpfr_rint' behaves like one of these four functions,
    depending on the rounding mode. Further to its usual meaning, $inex
    is 0 when $op is an integer representable in $rop, 1 or -1 when $op
    is an integer that is not representable in $rop, 2 or -2 when $op is
    not an integer.

    $inex = Rmpfr_rint_ceil($rop, $op, $rnd);
    $inex = Rmpfr_rint_floor($rop, $op, $rnd);
    $inex = Rmpfr_rint_round($rop, $op, $rnd);
    $inex = Rmpfr_rint_roundeven($rop, $op, $rnd);  # mpfr-4.0.0 & later
    $inex = Rmpfr_rint_trunc($rop, $op, $rnd);
     Set $rop to $op rounded to an integer. 'Rmpfr_rint_ceil' rounds to
     the next higher or equal integer, 'Rmpfr_rint_floor' to the next
     lower or equal integer, 'Rmpfr_rint_round' to the nearest integer,
     rounding halfway cases away from zero, 'Rmpfr_rint_roundeven' to
     the nearest integer,rounding halfway cases to the nearest even
     integer and 'Rmpfr_rint_trunc' to the next integer towards zero.
     If the result is not representable, it is rounded in the direction
     $rnd.

   $inex = Rmpfr_frac($rop, $op, $round);
    Set $rop to the fractional part of $op, having the same sign as $op,
    rounded in the direction $round (unlike in 'mpfr_rint', $round
    affects only how the exact fractional part is rounded, not how
    the fractional part is generated).

   $inex = Rmpfr_modf ($rop1, $rop2, $op, $rnd);
    Set simultaneously $rop1 to the integral part of $op and $rop2
    to the fractional part of $op, rounded in the direction RND with
    the corresponding precision of $rop1 and $rop2 (equivalent to
    'Rmpfr_trunc($rop1, $op, $rnd)' and 'Rmpfr_frac($rop1, $op, $rnd)').
    The variables $rop1 and $rop2 must be different. Return 0 if both
    results are exact.

   $inex         = Rmpfr_remainder($rop, $op1, $op2, $rnd);
   $inex         = Rmpfr_fmod($rop, $op1, $op2, $rnd);
   ($si2, $si) = Rmpfr_remquo  ($rop, $op1, $op2, $rnd);
   ($si2, $si) = Rmpfr_fmodquo ($rop, $op1, $op2, $rnd); # mpfr-4.0.0 &
                                                         # later only
    Set $rop to the value of $op - N*$op2, rounded according to the
    direction $rnd, where N is the integer quotient of $op1 divided by
    $op2, defined as follows: N is rounded toward zero for 'Rmpfr_fmod'
    and 'Rmpfr_fmodquo', and to the nearest integer (ties rounded to
    even) for 'mpfr_remainder' and 'mpfr_remquo'.
    Special values are handled as described in Section F.9.7.1 of the
    ISO C99 standard: If $op1 is infinite or $op2 is zero, $rop is NaN.
    If $op2 is infinite and $op1 is finite, $rop is $op1 rounded to
    the precision of $rop. If $rop is zero, it has the sign of $op1.
    The return value is the ternary value corresponding to $rop.
    Additionally, 'Rmpfr_remquo' and 'Rmpfr_fmodquo store the low
    significant bits from the quotient in $si2 (more precisely the
    number of bits in a 'long' minus one), with the sign of $op1
    divided by $op2 (except if those low bits are all zero, in which
    case zero is returned).  Note that $op1 may be so large in
    magnitude relative to $op2 that an exact representation of the
    quotient is not practical. 'Rmpfr_remainder' and Rmpfr_remquo'
    functions are useful for additive argument reduction.

   $inex = Rmpfr_fmod_ui($rop, $op1, $ui, $rnd);
    As for Rmpfr_fmod(), above, except that the 3rd arg is an
    unsigned long int instead of a Math::MPFR object. This function
    was introduced in mpfr-4.2.0-dev, but is implemented (suboptimally)
    in Math::MPFR built against older versions of the mpfr library.

   $bool = Rmpfr_integer_p($op);
    Return non-zero if $op is an integer.

   Rmpfr_nexttoward($op1, $op2);
    If $op1 or $op2 is NaN, set $op1 to NaN. Otherwise, if $op1 is
    different from $op2, replace $op1 by the next floating-point number
    (with the precision of $op1 and the current exponent range) in the
    direction of $op2, if there is one (the infinite values are seen as
    the smallest and largest floating-point numbers). If the result is
    zero, it keeps the same sign. No underflow or overflow is generated.

   Rmpfr_nextabove($op1);
    Equivalent to 'mpfr_nexttoward' where $op2 is plus infinity.

   Rmpfr_nextbelow($op1);
    Equivalent to 'mpfr_nexttoward' where $op2 is minus infinity.

   $inex = Rmpfr_min($rop, $op1, $op2, $round);
    Set $rop to the minimum of $op1 and $op2. If $op1 and $op2
    are both NaN, then $rop is set to NaN. If $op1 or $op2 is
    NaN, then $rop is set to the numeric value. If $op1 and
    $op2 are zeros of different signs, then $rop is set to -0.

   $inex = Rmpfr_max($rop, $op1, $op2, $round);
    Set $rop to the maximum of $op1 and $op2. If $op1 and $op2
    are both NaN, then $rop is set to NaN. If $op1 or $op2 is
    NaN, then $rop is set to the numeric value. If $op1 and
    $op2 are zeros of different signs, then $rop is set to +0.

   $IV = Math::MPFR::nnumflag(); # not exported
    Returns the value of the non-numeric flag. This flag is
    initialized to zero, but incremented by 1 whenever the
    a string containing non-numeric characters is passed to an
    mpfr function. The value of the flag therefore tells us how
    many times such strings were passed to mpfr functions . The
    flag can be reset to 0 by running clear_nnum().

   $IV = Math::MPFR::nok_pokflag(); # not exported
    Returns the value of the nok_pok flag. This flag is
    initialized to zero, but incremented by 1 whenever a
    scalar that is both a float (NOK) and string (POK) is passed
    to new() or to an overloaded operator. The value of the flag
    therefore tells us how many times such events occurred . The
    flag can be reset to 0 by running clear_nok_pok().

   Math::MPFR::set_nnum($IV); # not exported
    Resets the global non-numeric flag to the value specified by
    $IV.

   Math::MPFR::set_nok_pok($IV); # not exported
    Resets the nok_pok flag to the value specified by $IV.

   Math::MPFR::clear_nnum(); # not exported
    Resets the global non-numeric flag to 0.(Essentially the same
    as running set_nnum(0).)

   Math::MPFR::clear_nok_pok(); # not exported
    Resets the nok_pok flag to 0.(Essentially the same
    as running set_nok_pok(0).)

   $bytes = Math::MPFR::bytes($val, $bits);
    (The semantics for calling this function have changed as of
    Math-MPFR-4.13.)
    $val must either be a string (eg '1.613e-45', '2.3', '0x17.8')
    or a Math::MPFR object.
    $bits must be one of 53, 64, 2098 or 113.
    $bytes will be set to the hex representation of $val.
    If $bits is 53, $bytes will display the byte structure (in
    hex) of the standard 8-byte double, $val.
    If $bits is 64, the structure returned will be that of $val
    as an extended precision 10-byte long double.
    If $bits is 2098, the structure returned will be that of $val
    as the 16-byte IBM doubledouble.
    If $bits is 113, the structure returned will be that of $val
    as the quad precision 16-byte IEEE long double (or __float128,
    which is identical in byte structure).

    eg:
      bytes('1.3', 53)   returns 3ff4cccccccccccd
      bytes('1.3', 64)   returns 3fffa666666666666666
      bytes('1.3', 2098) returns 3ff4cccccccccccdbc8999999999999a
      bytes('1.3', 113)  returns 3fff4ccccccccccccccccccccccccccd

    If $val is a Math::MPFR object, its precision must be $bits.

    For many architectures and mpfr configurations, the structures
    for all 4 allowed values of $bits will be accessible.
    In some cases, however, $bits values of 64 and/or 113 might
    throw a fatal error (with diagnostic message stating that the
    requested byte structure is not currently available).

   $str = unpack_bfloat16($arg, $rnd, [$base]);# 16-bit "bfloat"
   $str = unpack_float16($arg, $rnd, [$base]); # 16-bit half prec.
   $str = unpack_float32($arg, $rnd, [$base]); # 32-bit single prec.
    The "bfloat16" and "float16" forms require mpfr-4.3.0 or later.
    They also require that Math::MPFR has been built with
    "__bf16" and (respectively) "_Float16" support.
    (The "float32" is simply the single precision "float", which
    should be universally supported.)
    $arg is one of IV, UV, NV, PV, or Math::MPFR object.
    Unpack $arg's value to an upper case hex string, where the
    value of $arg has been cast (in accordance with $rnd) to a
    __bf16 (bfloat) or  _Float16 or _Float32 type.
    $base is an optional argument specifying the base when $arg
    is a PV (string). If no $base argument is provided, then the
    base of the given PV is determined by using the approach
    specified in the Rmpfr_strtofr() documentation, provided
    above in the "ASSIGNMENT" section.
    For example:
      print unpack_bfloat16(-2.625, MPFR_RNDN); # Outputs C028
      print unpack_float16 (-2.625, MPFR_RNDN); # Outputs C140
      print unpack_float32 (-2.625, MPFR_RNDN); # Outputs C0280000

   $si = IOK_flag($sv); # $sv is a perl scalar variable.
   $si = NOK_flag($sv);
   $si = POK_flag($sv);

    Return 0 if $sv's IOK/NOK/POK flag is unset.
    Else return 1.
    If the IsUV flag is set, then IOK_flag() returns 2, thereby indicating
    that both the IOK and IsUV flags are set (and that the integer value
    held by $sv should therefore be treated as unsigned).

   ##############

   RANDOM NUMBERS

   Rmpfr_urandomb(@r, $state);
    Each member of @r is a Math::MPFR object.
    $state is a reference to a gmp_randstate_t structure.
    Set each member of @r to a uniformly distributed random
    float in the interval 0 <= $_ < 1.
    Before using this function you must first create $state
    by calling one of the 4 Rmpfr_randinit functions, then
    seed $state by calling one of the 2 Rmpfr_randseed functions.
    The memory associated with $state will be freed automatically
    when $state goes out of scope.

   Rmpfr_random2($rop, $si, $ui); # not implemented in
                                  # mpfr-3.0.0 and later
    Attempting to use this function when Math::MPFR has been
    built against mpfr-3.0.0 (or later) will cause the program
    to die, with an appropriate error message.
    Generate a random float of at most abs($si) limbs, with long
    strings of zeros and ones in the binary representation.
    The exponent of the number is in the interval -$ui to
    $ui.  This function is useful for testing functions and
    algorithms, since this kind of random numbers have proven
    to be more likely to trigger corner-case bugs.  Negative
    random numbers are generated when $si is negative.

   $si = Rmpfr_urandom ($rop, $state, $rnd);  # mpfr-3.0.0 and
                                              # later only
    Generate a uniformly distributed random float.  The
    floating-point number $rop can be seen as if a random real
    number is generated according to the continuous uniform
    distribution on the interval[0, 1] and then rounded in the
    direction RND.
    Before using this function you must first create $state
    by calling one of the Rmpfr_randinit functions (below), then
    seed $state by calling one of the Rmpfr_randseed functions.

   $si = Rmpfr_grandom($rop1, $rop2, $state, $rnd);
    Available only with mpfr-3.1.x. (Was deprecated in 4.0.0.)
    Use Rmpfr_nrandom() if Rmpfr_grandom() is unavailable.
    This function will croak with an appropriate message if
    Math::MPFR is built against an mpfr version other than 3.1.x.
    Generate two random floats according to a standard normal
    gaussian distribution. The floating-point numbers $rop1 and
    $rop2 can be seen as if a random real number were generated
    according to the standard normal gaussian distribution and
    then rounded in the direction $rnd.
    Before using this function you must first create $state
    by calling one of the Rmpfr_randinit functions (below), then
    seed $state by calling one of the Rmpfr_randseed functions.

   $si = Rmpfr_nrandom ($rop, $state, $rnd);  # mpfr-4.0.0 and
                                              # later only
    Generate a random floating-point number according to a standard
    normal Gaussian distribution (with mean zero and variance one).
    The floating-point number $rop can be seen as if a random real
    number were generated according to the standard normal Gaussian
    distribution and then rounded in the direction $rnd.
    This function is more efficient than Rmpfr_grandom.

   $si = Rmpfr_erandom($rop, $state, $rnd);  # mpfr-4.0.0 and
                                             # later only
     Generate one random floating-point number according to an
     exponential distribution, with mean one.  Other characteristics
     are identical to 'Rmpfr_nrandom'.

   $state = Rmpfr_randinit_default();
    Initialise $state with a default algorithm. This will be
    a compromise between speed and randomness, and is
    recommended for applications with no special requirements.

   $state = Rmpfr_randinit_mt();
    Initialize state for a Mersenne Twister algorithm. This
    algorithm is fast and has good randomness properties.

   $state = Rmpfr_randinit_lc_2exp($a, $c, $m2exp);
    This function is not tested in the test suite.
    Use with caution - I often select values here that cause
    Rmpf_urandomb() to behave non-randomly.
    Initialise $state with a linear congruential algorithm:
    X = ($a * X + $c) % 2 ** $m2exp
    The low bits in X are not very random - for this reason
    only the high half of each X is actually used.
    $c and $m2exp are both unsigned longs.
    $a can be any one of Math::GMP, or Math::GMPz objects.
    Or it can be a string.
    If it is a string of hex digits it must be prefixed with
    either OX or Ox. If it is a string of octal digits it must
    be prefixed with 'O'. Else it is assumed to be a decimal
    integer. No other bases are allowed.

   $state = Rmpfr_randinit_lc_2exp_size($ui);
    Initialise state as per Rmpfr_randinit_lc_2exp. The values
    for $a, $c and $m2exp are selected from a table, chosen
    so that $ui bits (or more) of each X will be used.

   Rmpfr_randseed($state, $seed);
    $state is a reference to a gmp_randstate_t structure (the
    return value of one of the Rmpfr_randinit functions).
    $seed is the seed. It can be any one of Math::GMP,
    or Math::GMPz objects. Or it can be a string of digits.
    If it is a string of hex digits it must be prefixed with
    either OX or Ox. If it is a string of octal digits it must
    be prefixed with 'O'. Else it is assumed to be a decimal
    integer. No other bases are allowed.

   Rmpfr_randseed_ui($state, $ui);
    $state is a reference to a gmp_randstate_t structure (the
    return value of one of the Rmpfr_randinit functions).
    $ui is the seed.

   #########

   INTERNALS

   $bool = Rmpfr_can_round($op, $ui, $rnd1, $rnd2, $p);
    Assuming $op is an approximation of an unknown number X in direction
    $rnd1 with error at most two to the power E(b)-$ui where E(b) is
    the exponent of $op, returns 1 if one is able to round exactly X
    to precision $p with direction $rnd2, and 0 otherwise. This
    function *does not modify* its arguments.

   $str = Rmpfr_print_rnd_mode($rnd);
    Return a string ("MPFR_RNDD", "MPFR_RNDU", "MPFR_RNDN", "MPFR_RNDZ",
    "MPFR_RNDA") corresponding to the rounding mode $rnd, or return
    undef if $rnd is an invalid rounding mode.

   $si = Rmpfr_get_exp($op);
    Return to $si the exponent of $op.
    The behavior for nan, infinity or zero is undefined.

   $si = Rmpfr_set_exp($op, $si);
    Set the exponent of $op if $si is in the current exponent
    range, and return 0 (even if $op is not a non-zero
    ordinary number); otherwise, return a non-zero value.

   $si = Rmpfr_signbit ($op);
    Return a non-zero value if $op has its sign bit set (i.e. if it is
    negative, -0, or a NaN whose representation has its sign bit set).

   $si2 = Rmpfr_setsign ($rop, $op, $si, $rnd);
    Set the value of $rop from $op, rounded towards the given direction
    $rnd, then set/clear its sign bit if $si is true/false (even when
    $op is a NaN).

   $si = Rmpfr_copysign ($rop, $op1, $op2, $rnd);
    Set the value of $rop from $op1, rounded towards the given direction
    $rnd, then set its sign bit to that of $op2 (even when $op1 or $op2
    is a NaN). This function is equivalent to:
    Rmpfr_setsign ($rop, $op1, Rmpfr_signbit ($op2), $rnd)'.

   ####################

   OPERATOR OVERLOADING

    Overloading works with numbers, strings (bases 2, 10, and 16
    only - see step '3.' below) and Math::MPFR objects.
    Overloaded operations are performed using the current
    "default rounding mode" (which you can determine using the
    'Rmpfr_get_default_rounding_mode' function, and change using
    the 'Rmpfr_set_default_rounding_mode' function).

    Be aware that when you use overloading with a string operand,
    the overload subroutine converts that string operand to a
    Math::MPFR object with *current default precision*, and using
    the *current default rounding mode*.

    Note that any comparison using the spaceship operator ( <=> )
    will return undef if either/both of the operands is a NaN.
    Any comparison ( < <= > >= == != <=> ) involving one or more
    NaNs will set the erange flag.

    For the purposes of the overloaded 'not', '!' and 'bool'
    operators, a "false" Math::MPFR object is one whose value is
    either 0 (including -0) or NaN.
    (A "true" Math::MPFR object is, of course, simply one that
    is not "false".)

    The following operators are overloaded:
     + - * / % ** sqrt (Return object has default precision)
     += -= *= /= %= **= ++ -- (Precision remains unchanged)
     < <= > >= == != <=>
     ! bool
     abs atan2 cos sin log exp (Return object has default precision)
     int (On perl 5.8+ only, NA on perl 5.6. The return object
          has default precision)

     ""  (Interpolates the value of the Math::MPFR object to a
          decimal string)

     << >> <<= >>= (The Math::MPFR object is first truncated to an integer
                    value. Left shifts will increase the exponent by the
                    value of the given " left shift" argument. For right
                    shifts, the Math::MPFR object's value is then altered
                    according to the rules of integer right shifts.
                    Thereby, for both left and right shifts the resultant
                    value of the object is an integer value.
                    Negative values for the 'shift' argument are allowed,
                    in which case the shift value is multiplied by -1
                    and the direction of the shift is reversed.
                    This is consistent with perl's shifting of NVs.)

     = (The copy has the same precision as the copied object.)

    NOTE: Making use of the '=' overloading is not recommended unless
          you understand its caveats. See 'perldoc overload' and
          read it thoroughly, including the documentation regarding
          'copy constructors'.

    Furthermore, all overloaded comparisons ( < <= > >= == != <=> )
    between Math::MPFR and Math::GMPz objects or between Math::MPFR
    and Math::GMPq objects are permitted.
    Comparison operations between Math::MPFR and Math::GMP objects
    must be constructed such that Math::MPFR (not Math::GMP)
    overloading is invoked.

    Some additional cross-class overloading is also allowed.
    Let $M be a Math::MPFR object, and $G be any one of a Math::GMPz,
    Math::GMPq, or Math::GMP object. Then it is permissible to do:

     $M + $G;
     $M += $G;
     $M - $G;
     $M -= $G;
     $M * $G;
     $M *= $G;
     $M / $G;
     $M /= $G;
     $M % $G;  (Wraps the mpfr_fmod function)
     $M %= $G; (Wraps the mpfr_fmod function)
     $M ** $G;
     $M **= $G;

    YMMV if you use old versions of Math::GMPz and Math::GMPq.
    But if you have Math-GMPz-0.63 (or later) and Math-GMPq-0.61
    (or later), and $G is either a Math::GMPz or Math::GMPq
    object, then it is also permissible to do the following - all
    of which will overwrite the Math::GMPz/q object ($G) with
    the Math::MPFR object that these operations return:

     $G + $M;
     $G += $M;
     $G - $M;
     $G -= $M;
     $G * $M;
     $G *= $M;
     $G / $M;
     $G /= $M;
     $G % $M;  (Wraps the mpfr_fmod function)
     $G %= $M; (Wraps the mpfr_fmod function)
     $G ** $M;
     $G **= $M;

    NOTE: In cross-class overloading a ** (power) or % (mpfr_fmod)
    operation that involves a Math::GMPq object, the value of the
    Math::GMPq object is assigned to a Math::MPFR object - using
    current default precision and current default rounding mode.
    Otherwise, the argument $G will be evaluated to "infinite"
    precision.
    The returned (Math::MPFR object) result will have been rounded
    to default precision, using default rounding mode.

    The following cross-class overloading is also available if
    version 1.40 (or later) of Math::MPC is installed. "$MPC"
    denotes a Math::MPC object.
    IMPORTANTLY, please note that all of these operations return
    a Math::MPC object, and the testing of these functions is
    performed only by the Math::MPC test suite:

    $MPC +  $M; and $M +  $MPC;
    $MPC += $M; and $M += $MPC;
    $MPC -  $M; and $M -  $MPC;
    $MPC -= $M; and $M -= $MPC;
    $MPC *  $M; and $M *  $MPC;
    $MPC *= $M; and $M *= $MPC;
    $MPC /  $M; and $M /  $MPC;
    $MPC /= $M; and $M /= $MPC;
    $MPC **  $M; and $M **  $MPC;
    $MPC **= $M; and $M **= $MPC;

    To determine the type and value of the second argument received
    by the overloading subroutines, we work through the following
    steps (in order), using the first value we find, or croaking if
    we get to step 6:

    1. If the variable is a UV then that value is used. The variable
       is considered to be a UV if the IOK and IsUV flags are set.

    2. If the variable is an IV, then that value is used.
       The variable is considered to be an IV if the IOK flag is set.

    3. If the variable is a string (ie the POK flag is set) then the
       value of that string is used. If the POK flag is set, but the
       string is not a valid number, the subroutine croaks with an
       appropriate error message. If the string starts with '0b' or
       '0B' it is regarded as a base 2 number. If it starts with '0x'
       or '0X' it is regarded as a base 16 number. Otherwise it is
       regarded as a base 10 number.
       The value is then handed to a temporary Math::MPFR object that
       has current default precision. Any rounding required will be
       done in accordance with current default rounding mode.
       See "STRING OVERLOADING ANOMALY" (below) for an example of
       possible anomalies regarding string overloading.

    4. If the variable is an NV (floating point value) then that
       value is used. The variable is considered to be an NV if the
       NOK flag is set.
       Note therefore, that if the variable is both an NV (NOK flag
       set) and PV (POK flag also set) then the string value in the
       PV slot will be used. This is probably, but not necessarily,
       what you want, and it's recommended not to pass such values
       to the overloaded operators.

    5. If the variable is a Math::MPFR, Math::GMPz, or Math::GMPq,
       or Math::GMP object then the value of that object is used.
       For some operations a Math::GMP object will not be accepted,
       in which case the operation will die with an appropriate
       error message. If the variable is a Math::MPC object && the
       version of Math::MPC >= 1.40, then the value of that object
       is used, with all processing being done by Math::MPC.

    6. If none of the above is true, then the second variable is
       deemed to be of an invalid type. The operation croaks with
       an appropriate error message.

   ############################

   UNEXPORTED UTILITY FUNCTIONS

   These may (or may not) be useful in examining or tweaking strings
   that, having been allocated in perl space, are then assigned some
   value in an XSub such as Rmpfr_fpif_export() or Rmpfr_sprintf().

   $uv = _strlen($str);
     Returns the length of the string $string as assessed by C's
     strlen function. This can differ from length($str).

   $uv = _SvCUR($str);
     Returns the CUR value (in bytes) of $str. This will be the same
     as length($str) if $string contains no multi-byte characters.
     See "SvCUR" in the perlapi documentation.

   $uv = _SvLEN($str);
     Returns the size of the string buffer (in bytes) in the SV.
     See "SvLEN" in the perlapi documentation.

   _SvCUR_set($str, $uv);
     Set the CUR of $str to $uv bytes.
     See "SvCUR_set" in the perlapi documentation.

   ##########################

   STRING OVERLOADING ANOMALY

    An example, when $Config{ivsize} == 8, default precision <= 63,
    default rounding mode is either MPFR_RNDN, MPFR_RNDU or MPFR_RNDA :

      my $f = Math::MPFR->new(2 ** 64); # 0x1p+64
      my $i = 18446744073709551615;     # 1 less than 2 ** 64
      print ($f <=>  $i ); # prints 1
      print ($f <=> "$i"); # prints 0

    If you want an integer string in an overloaded expression to be
    evaluated to its full (arbitrary) precision, then convert it to a
    Math::GMPz object first:

      print ($f <=> Math::GMPz->new("$i")); # prints 1

    See t/anomaly.t in the test suite for further examples.

   #####################

   FORMATTED OUTPUT

   NOTE: Bear in mind that, if the variable to be formatted by
         Rmpfr_printf/Rmpfr_fprintf/Rmpfr_sprintf/Rmpfr_snprintf
         is a normal perl string or numeric scalar (ie PV or IV or
         NV) then the formatting will actually be handled by the
         underlying gmp/mpfr C functionality, and not by the (more
         lenient) perl formatting functionality.
         For example, Rmpfr_printf("%.17g", 65416) will output
         rubbish, while printf("%.17g", 65416) will output 65416.
         But then ... why would you invoke Rmpfr_printf to do
         something when you have perl to DWYM ?

   NOTE: Frankly, I don't see any point in using the 'P' (precision)
         specifier in a perl environment. In perl, you can simply do:

           $prec = Rmpfr_get_prec($obj);
           print $prec;

         Why would anyone want to replace that second line with (eg):
           Rmpfr_printf("%Pd\n", $prec);

         Nevertheless, it is currently allowable to use the 'P'
         specifier with Math::MPFR's formatting functions - but
         there's a caveat. If $Config{ivsize} is greater than the size
         of the mpfr library's mpfr_prec_t type && the machine
         architecture is big-endian, then (AFAIK) using the 'P'
         specifier as just demonstrated can produce incorrect output.
         In such a case, the example needs to be rewritten as:
           Rmpfr_printf("%Pd\n", prec_cast($prec));

         The Math::MPFR::Prec package (which is part of the Math::MPFR
         distribution) exists solely to provide this prec_cast sub.
         And the prec_cast sub's return value should be passed *only*
         to the 'P' type specifier. Nothing else will understand it.
         At some point in the future, I might do a sensible thing - and
         remove both Math::MPFR::Prec and perl's support of the 'P'
         specifier from Math::MPFR.

   prec_cast($prec);
    Ensures that the 'P' type specifier will provide correct results.
    I found that simply doing (eg) :
      Rmpfr_printf("%Pu\n", Rmpfr_get_prec($op));
    did not work correctly for all perl configurations.
    For portability, that line needs to be written as:
      Rmpfr_printf("%Pu\n", prec_cast(Rmpfr_get_prec($op)));
    I recommend that one instead does:
     print Rmpfr_get_prec($op), "\n";

   Rmpfr_printf($format_string, [$rnd,] $var);

    This function (unlike the MPFR counterpart) is limited to taking
    2 or 3 arguments - the format string, optionally a rounding argument,
    and the variable to be formatted.
    That is, you can currently Rmpfr_printf only one variable at a time.
    If there's no variable to be formatted, just add a '0' as the final
    argument. ie this will work fine:
     Rmpfr_printf("hello world\n", 0);
    NOTE: The rounding argument $rnd can be provided *only* if $var is a
          Math::MPFR object. To do otherwise is a fatal error.
          A better way (IMO) to specify the rounding arg is to include it
          in the formatting spec. For example, instead of doing:
            Rmpfr_printf("%.17R*g\n", MPFR_RNDU, $op);
            do:
            Rmpfr_printf("%.17RUg\n", $op);
    See the mpfr documentation for details re the formatting options:
    http://www.mpfr.org/mpfr-current/mpfr.html#Formatted-Output-Functions

   Rmpfr_fprintf($fh, $format_string, [$rnd,] $var);

    This function (unlike the MPFR counterpart) is limited to taking
    3 or 4 arguments - the filehandle, the format string, optionally a
    rounding argument, and the variable to be formatted. That is, you
    can Rmpfr_fprintf only one variable at a time.
    If there's no variable to be formatted, just add a '0' as the final
    argument. ie this will work fine:
     Rmpfr_fprintf($fh, "hello world\n", 0);
    NOTE: The rounding argument $rnd can be provided *only* if $var is a
          Math::MPFR object. To do otherwise is a fatal error.
          As for Rmpfr_printf (above), the rounding argument can be given
          in the formatting spec, rather than as a separate argument.
    See the mpfr documentation for details re the formatting options:
    http://www.mpfr.org/mpfr-current/mpfr.html#Formatted-Output-Functions

   Rmpfr_sprintf($buffer, $format_string, [$rnd,] $var, $buflen);

    This function (unlike the MPFR counterpart) is limited to taking
    4 or 5 arguments - the buffer (which does not have to be
    initialized), the format string, optionally a rounding argument,
    the variable to be formatted, and the size of the buffer ($buflen)
    into which the result will be written.
    $buflen  must specify a size (bytes) that is at least large
    enough to accommodate the formatted string (including the
    terminating NULL). The formatted string will be placed in $buffer.
    If there's no variable to be formatted, just insert a '0' as the
    value for $var. ie this will work fine:
     Rmpfr_sprintf($buffer, "hello world", 0, $buflen);
    NOTE: The rounding argument $rnd can be provided *only* if $var is a
          Math::MPFR object. To do otherwise is a fatal error.
          As for Rmpfr_printf (above), the rounding argument can be given
          in the formatting spec, rather than as a separate argument.
    See the mpfr documentation for details re the formatting options:
    http://www.mpfr.org/mpfr-current/mpfr.html#Formatted-Output-Functions

   Rmpfr_snprintf($buffer, $bytes, $format_string, [$rnd,] $var, $buflen);

    This function (unlike the MPFR counterpart) is limited to taking
    5 or 6 arguments - the buffer (which dowes not have to be
    initialized), the number of bytes to be written, the format string,
    optionally a rounding argument, the variable to be formatted and
    the size of the buffer ($buflen).
    $buflen must  specify a size (bytes) that is at least large
    enough to accommodate the formatted string (including the
    terminating NULL). The formatted string will be placed in $buffer.
    If there's no variable to be formatted, just insert a '0' as the
    value for $arg. ie this will work fine:
     Rmpfr_snprintf($buffer, 12, "hello world", 0, $buflen);
    NOTE: The rounding argument $rnd can be provided *only* if $var is a
          Math::MPFR object. To do otherwise is a fatal error.
          As for Rmpfr_printf (above), the rounding argument can be given
          in the formatting spec, rather than as a separate argument.
    See the mpfr documentation for further details:
    http://www.mpfr.org/mpfr-current/mpfr.html#Formatted-Output-Functions

   #####################

   BASE CONVERSIONS

   $DBL_DIG  = MPFR_DBL_DIG;  # Will be undef if float.h doesn't define
                              # DBL_DIG.

   $LDBL_DIG = MPFR_LDBL_DIG; # Will be undef if float.h doesn't define
                              # LDBL_DIG.

   $FLT128_DIG = MPFR_FLT128_DIG; # Will be undef if quadmath.h has not
                                  # been loaded, or quadmath.h does not
                                  # define FLT128_DIG
.
   $min_prec = mpfr_min_inter_prec($orig_base, $orig_prec, $to_base);

     NOTE: $min_prec can be (very rarely) off by one if $orig_prec is in
           the millions, or if either $orig_base or $to_base are
           outside of the range 2..64.

     Example 1:
     Let's say we have some base 10 integers comprising 16 base 10
     digits, and we want to represent those numbers in base 2 (binary).
     What is the minimum required number of bits, such that it can be
     guaranteed that converting the base 2 representations back to base
     10 will result in the original 16 digit representations ?

     We can calculate that minimum required precision with:
       $min_prec = mpfr_min_inter_prec($orig_base, $orig_prec, $to_base);

     In this example case that becomes:
     $min_prec = mpfr_min_inter_prec(10, 16, 2);
     which will set $min_prec to 55.

     That is, so long as our base 2 representations provide at least 55
     bits, we can pass 16-digit, base 10, integer values to them,
     and be assured of retrieving the original base 10 representation when
     we convert the base 2 representations back to base 10.
     Sure ... not all 16-digit values require 55 bits, but there are some
     that do ... and there are none that require more than 55 bits.

     Example 2:
     $min_prec = mpfr_min_inter_prec(2, 53, 10);
     $min_prec is set to 17.
     This tells us that a base 10 representation of a 53-bit integer needs
     to comprise at least 17 digits if we are to be assured that assigning
     that base 10 representation to a 53-bit integer will result in a
     53-bit integer that is identical to the first.
     Otherwise, there is no such assurance.

   $max_prec = mpfr_max_orig_prec ($orig_base, $to_base, $to_prec);

     NOTE: $max_prec can be (very rarely) off by one if $to_prec is in
           the millions, or if either $orig_base or $to_base are
           outside of the range 2..64.

     For example:
     To determine the maximum significant number of base 10 digits that
     can be specified, when assigning to a 53-bit double. We have:

     $max_len = mpfr_max_orig_len($orig_base, $to_base, $to_prec);

     For this example that becomes:

     $max_len = mpfr_max_orig_len(10, 2, 53);

     which will set $max_len to 15.
     That is, so long as our base 10 integer consists of no more than
     15 significant digits, we can assign it to a 53-bit double and be
     assured of retrieving the original value upon converting that
     double back to a 15-digit base 10 representation.
     Otherwise, there is no such assurance.

     It is to be expected that
      mpfr_max_orig_len(10, 2, 53) == DBL_DIG
      and
      mpfr_max_orig_len(10, 2, 113) == FLT128_DIG
      and
      mpfr_max_orig_len(10, 2, $long_double_prec) == LDBL_DIG

     (where $long_double_prec is the precision, in bits, of the
     the C 'long double' type - usually either 53 or 64 or 113.)

   #####################

TODO
    Look at wrapping mpfr_mp_memory_cleanup, mp_set_memory_functions

BUGS
    You can get segfaults if you pass the wrong type of argument to the
    functions - so if you get a segfault, the first thing to do is to
    check that the argument types you have supplied are appropriate.

ACKNOWLEDGEMENTS
    Thanks to Vincent Lefevre for providing corrections to errors
    and omissions, and suggesting improvements (which were duly
    put in place).

LICENSE
    This program is free software; you may redistribute it and/or
    modify it under the same terms as Perl itself.
    Copyright 2006-2026 Sisyphus

AUTHOR
    Sisyphus <sisyphus at(@) cpan dot (.) org>