1/*
2 * $Header: compress.c,v 4.0 85/07/30 12:50:00 joe Release $
3 * $Log:	compress.c,v $
4 * Revision 4.0  85/07/30  12:50:00  joe
5 * Removed ferror() calls in output routine on every output except first.
6 * Prepared for release to the world.
7 *
8 * Revision 3.6  85/07/04  01:22:21  joe
9 * Remove much wasted storage by overlaying hash table with the tables
10 * used by decompress: tab_suffix[1<<BITS], stack[8000].  Updated USERMEM
11 * computations.  Fixed dump_tab() DEBUG routine.
12 *
13 * Revision 3.5  85/06/30  20:47:21  jaw
14 * Change hash function to use exclusive-or.  Rip out hash cache.  These
15 * speedups render the megamemory version defunct, for now.  Make decoder
16 * stack global.  Parts of the RCS trunks 2.7, 2.6, and 2.1 no longer apply.
17 *
18 * Revision 3.4  85/06/27  12:00:00  ken
19 * Get rid of all floating-point calculations by doing all compression ratio
20 * calculations in fixed point.
21 *
22 * Revision 3.3  85/06/24  21:53:24  joe
23 * Incorporate portability suggestion for M_XENIX.  Got rid of text on #else
24 * and #endif lines.  Cleaned up #ifdefs for vax and interdata.
25 *
26 * Revision 3.2  85/06/06  21:53:24  jaw
27 * Incorporate portability suggestions for Z8000, IBM PC/XT from mailing list.
28 * Default to "quiet" output (no compression statistics).
29 *
30 * Revision 3.1  85/05/12  18:56:13  jaw
31 * Integrate decompress() stack speedups (from early pointer mods by McKie).
32 * Repair multi-file USERMEM gaffe.  Unify 'force' flags to mimic semantics
33 * of SVR2 'pack'.  Streamline block-compress table clear logic.  Increase
34 * output byte count by magic number size.
35 *
36 * Revision 3.0   84/11/27  11:50:00  petsd!joe
37 * Set HSIZE depending on BITS.  Set BITS depending on USERMEM.  Unrolled
38 * loops in clear routines.  Added "-C" flag for 2.0 compatibility.  Used
39 * unsigned compares on Perkin-Elmer.  Fixed foreground check.
40 *
41 * Revision 2.7   84/11/16  19:35:39  ames!jaw
42 * Cache common hash codes based on input statistics; this improves
43 * performance for low-density raster images.  Pass on #ifdef bundle
44 * from Turkowski.
45 *
46 * Revision 2.6   84/11/05  19:18:21  ames!jaw
47 * Vary size of hash tables to reduce time for small files.
48 * Tune PDP-11 hash function.
49 *
50 * Revision 2.5   84/10/30  20:15:14  ames!jaw
51 * Junk chaining; replace with the simpler (and, on the VAX, faster)
52 * double hashing, discussed within.  Make block compression standard.
53 *
54 * Revision 2.4   84/10/16  11:11:11  ames!jaw
55 * Introduce adaptive reset for block compression, to boost the rate
56 * another several percent.  (See mailing list notes.)
57 *
58 * Revision 2.3   84/09/22  22:00:00  petsd!joe
59 * Implemented "-B" block compress.  Implemented REVERSE sorting of tab_next.
60 * Bug fix for last bits.  Changed fwrite to putchar loop everywhere.
61 *
62 * Revision 2.2   84/09/18  14:12:21  ames!jaw
63 * Fold in news changes, small machine typedef from thomas,
64 * #ifdef interdata from joe.
65 *
66 * Revision 2.1   84/09/10  12:34:56  ames!jaw
67 * Configured fast table lookup for 32-bit machines.
68 * This cuts user time in half for b <= FBITS, and is useful for news batching
69 * from VAX to PDP sites.  Also sped up decompress() [fwrite->putc] and
70 * added signal catcher [plus beef in writeerr()] to delete effluvia.
71 *
72 * Revision 2.0   84/08/28  22:00:00  petsd!joe
73 * Add check for foreground before prompting user.  Insert maxbits into
74 * compressed file.  Force file being uncompressed to end with ".Z".
75 * Added "-c" flag and "zcat".  Prepared for release.
76 *
77 * Revision 1.10  84/08/24  18:28:00  turtlevax!ken
78 * Will only compress regular files (no directories), added a magic number
79 * header (plus an undocumented -n flag to handle old files without headers),
80 * added -f flag to force overwriting of possibly existing destination file,
81 * otherwise the user is prompted for a response.  Will tack on a .Z to a
82 * filename if it doesn't have one when decompressing.  Will only replace
83 * file if it was compressed.
84 *
85 * Revision 1.9  84/08/16  17:28:00  turtlevax!ken
86 * Removed scanargs(), getopt(), added .Z extension and unlimited number of
87 * filenames to compress.  Flags may be clustered (-Ddvb12) or separated
88 * (-D -d -v -b 12), or combination thereof.  Modes and other status is
89 * copied with copystat().  -O bug for 4.2 seems to have disappeared with
90 * 1.8.
91 *
92 * Revision 1.8  84/08/09  23:15:00  joe
93 * Made it compatible with vax version, installed jim's fixes/enhancements
94 *
95 * Revision 1.6  84/08/01  22:08:00  joe
96 * Sped up algorithm significantly by sorting the compress chain.
97 *
98 * Revision 1.5  84/07/13  13:11:00  srd
99 * Added C version of vax asm routines.  Changed structure to arrays to
100 * save much memory.  Do unsigned compares where possible (faster on
101 * Perkin-Elmer)
102 *
103 * Revision 1.4  84/07/05  03:11:11  thomas
104 * Clean up the code a little and lint it.  (Lint complains about all
105 * the regs used in the asm, but I'm not going to "fix" this.)
106 *
107 * Revision 1.3  84/07/05  02:06:54  thomas
108 * Minor fixes.
109 *
110 * Revision 1.2  84/07/05  00:27:27  thomas
111 * Add variable bit length output.
112 *
113 */
114
115static char rcs_ident[] =
116	"$Header: compress.c,v 4.0 85/07/30 12:50:00 joe Release $";
117