
/*
 * $Header: compress.c,v 4.0 85/07/30 12:50:00 joe Release $
 *
 * Revision 4.0  85/07/30  12:50:00  joe
 * Removed ferror() calls in output routine on every output except first.
 * Prepared for release to the world.
 * 
 * Revision 3.6  85/07/04  01:22:21  joe
 * Remove much wasted storage by overlaying hash table with the tables
 * used by decompress: tab_suffix[1<<BITS], stack[8000].  Updated USERMEM
 * computations.  Fixed dump_tab() DEBUG routine.
 *
 * Revision 3.5  85/06/30  20:47:21  jaw
 * Change hash function to use exclusive-or.  Rip out hash cache.  These
 * speedups render the megamemory version defunct, for now.  Make decoder
 * stack global.  Parts of the RCS trunks 2.7, 2.6, and 2.1 no longer apply.
 *
 * Revision 3.4  85/06/27  12:00:00  ken
 * Get rid of all floating-point calculations by doing all compression ratio
 * calculations in fixed point.
 *
 * Revision 3.3  85/06/24  21:53:24  joe
 * Incorporate portability suggestion for M_XENIX.  Got rid of text on #else
 * and #endif lines.  Cleaned up #ifdefs for vax and interdata.
 *
 * Revision 3.2  85/06/06  21:53:24  jaw
 * Incorporate portability suggestions for Z8000, IBM PC/XT from mailing list.
 * Default to "quiet" output (no compression statistics).
 *
 * Revision 3.1  85/05/12  18:56:13  jaw
 * Integrate decompress() stack speedups (from early pointer mods by McKie).
 * Repair multi-file USERMEM gaffe.  Unify 'force' flags to mimic semantics
 * of SVR2 'pack'.  Streamline block-compress table clear logic.  Increase 
 * output byte count by magic number size.
 * 
 * Revision 3.0   84/11/27  11:50:00  petsd!joe
 * Set HSIZE depending on BITS.  Set BITS depending on USERMEM.  Unrolled
 * loops in clear routines.  Added "-C" flag for 2.0 compatibility.  Used
 * unsigned compares on Perkin-Elmer.  Fixed foreground check.
 *
 * Revision 2.7   84/11/16  19:35:39  ames!jaw
 * Cache common hash codes based on input statistics; this improves
 * performance for low-density raster images.  Pass on #ifdef bundle
 * from Turkowski.
 *
 * Revision 2.6   84/11/05  19:18:21  ames!jaw
 * Vary size of hash tables to reduce time for small files.
 * Tune PDP-11 hash function.
 *
 * Revision 2.5   84/10/30  20:15:14  ames!jaw
 * Junk chaining; replace with the simpler (and, on the VAX, faster)
 * double hashing, discussed within.  Make block compression standard.
 *
 * Revision 2.4   84/10/16  11:11:11  ames!jaw
 * Introduce adaptive reset for block compression, to boost the rate
 * another several percent.  (See mailing list notes.)
 *
 * Revision 2.3   84/09/22  22:00:00  petsd!joe
 * Implemented "-B" block compress.  Implemented REVERSE sorting of tab_next.
 * Bug fix for last bits.  Changed fwrite to putchar loop everywhere.
 *
 * Revision 2.2   84/09/18  14:12:21  ames!jaw
 * Fold in news changes, small machine typedef from thomas,
 * #ifdef interdata from joe.
 *
 * Revision 2.1   84/09/10  12:34:56  ames!jaw
 * Configured fast table lookup for 32-bit machines.
 * This cuts user time in half for b <= FBITS, and is useful for news batching
 * from VAX to PDP sites.  Also sped up decompress() [fwrite->putc] and
 * added signal catcher [plus beef in writeerr()] to delete effluvia.
 *
 * Revision 2.0   84/08/28  22:00:00  petsd!joe
 * Add check for foreground before prompting user.  Insert maxbits into
 * compressed file.  Force file being uncompressed to end with ".Z".
 * Added "-c" flag and "zcat".  Prepared for release.
 *
 * Revision 1.10  84/08/24  18:28:00  turtlevax!ken
 * Will only compress regular files (no directories), added a magic number
 * header (plus an undocumented -n flag to handle old files without headers),
 * added -f flag to force overwriting of possibly existing destination file,
 * otherwise the user is prompted for a response.  Will tack on a .Z to a
 * filename if it doesn't have one when decompressing.  Will only replace
 * file if it was compressed.
 *
 * Revision 1.9  84/08/16  17:28:00  turtlevax!ken
 * Removed scanargs(), getopt(), added .Z extension and unlimited number of
 * filenames to compress.  Flags may be clustered (-Ddvb12) or separated
 * (-D -d -v -b 12), or combination thereof.  Modes and other status is
 * copied with copystat().  -O bug for 4.2 seems to have disappeared with
 * 1.8.
 *
 * Revision 1.8  84/08/09  23:15:00  joe
 * Made it compatible with vax version, installed jim's fixes/enhancements
 *
 * Revision 1.6  84/08/01  22:08:00  joe
 * Sped up algorithm significantly by sorting the compress chain.
 *
 * Revision 1.5  84/07/13  13:11:00  srd
 * Added C version of vax asm routines.  Changed structure to arrays to
 * save much memory.  Do unsigned compares where possible (faster on
 * Perkin-Elmer)
 *
 * Revision 1.4  84/07/05  03:11:11  thomas
 * Clean up the code a little and lint it.  (Lint complains about all
 * the regs used in the asm, but I'm not going to "fix" this.)
 *
 * Revision 1.3  84/07/05  02:06:54  thomas
 * Minor fixes.
 *
 * Revision 1.2  84/07/05  00:27:27  thomas
 * Add variable bit length output.
 *
 */

static char rcs_ident[] =
	"$Header: compress.c,v 4.0 85/07/30 12:50:00 joe Release $";
