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C/C++ Source or Header | 1993-11-08 | 28.5 KB | 763 lines

/* deflate.c -- compress data using the deflation algorithm * Copyright (C) 1992-1993 Jean-loup Gailly * This is free software; you can redistribute it and/or modify it under the * terms of the GNU General Public License, see the file COPYING. */ /* * Modified:1993 by SPDsoft for MacGzip * */ /* * PURPOSE * * Identify new text as repetitions of old text within a fixed- * length sliding window trailing behind the new text. * * DISCUSSION * * The "deflation" process depends on being able to identify portions * of the input text which are identical to earlier input (within a * sliding window trailing behind the input currently being processed). * * The most straightforward technique turns out to be the fastest for * most input files: try all possible matches and select the longest. * The key feature of this algorithm is that insertions into the string * dictionary are very simple and thus fast, and deletions are avoided * completely. Insertions are performed at each input character, whereas * string matches are performed only when the previous match ends. So it * is preferable to spend more time in matches to allow very fast string * insertions and avoid deletions. The matching algorithm for small * strings is inspired from that of Rabin & Karp. A brute force approach * is used to find longer strings when a small match has been found. * A similar algorithm is used in comic (by Jan-Mark Wams) and freeze * (by Leonid Broukhis). * A previous version of this file used a more sophisticated algorithm * (by Fiala and Greene) which is guaranteed to run in linear amortized * time, but has a larger average cost, uses more memory and is patented. * However the F&G algorithm may be faster for some highly redundant * files if the parameter max_chain_length (described below) is too large. * * ACKNOWLEDGEMENTS * * The idea of lazy evaluation of matches is due to Jan-Mark Wams, and * I found it in 'freeze' written by Leonid Broukhis. * Thanks to many info-zippers for bug reports and testing. * * REFERENCES * * APPNOTE.TXT documentation file in PKZIP 1.93a distribution. * * A description of the Rabin and Karp algorithm is given in the book * "Algorithms" by R. Sedgewick, Addison-Wesley, p252. * * Fiala,E.R., and Greene,D.H. * Data Compression with Finite Windows, Comm.ACM, 32,4 (1989) 490-595 * * INTERFACE * * void lm_init (int pack_level, ush *flags) * Initialize the "longest match" routines for a new file * * ulg deflate (void) * Processes a new input file and return its compressed length. Sets * the compressed length, crc, deflate flags and internal file * attributes. */ #include <stdio.h> #include "tailor.h" #include "gzip.h" #include "lzw.h" /* just for consistency checking */ #ifdef RCSID static char rcsid[] = "$Id: deflate.c,v 0.15 1993/06/24 10:53:53 jloup Exp $"; #endif /* =========================================================================== * Configuration parameters */ /* Compile with MEDIUM_MEM to reduce the memory requirements or * with SMALL_MEM to use as little memory as possible. Use BIG_MEM if the * entire input file can be held in memory (not possible on 16 bit systems). * Warning: defining these symbols affects HASH_BITS (see below) and thus * affects the compression ratio. The compressed output * is still correct, and might even be smaller in some cases. */ #ifdef SMALL_MEM # define HASH_BITS 13 /* Number of bits used to hash strings */ #endif #ifdef MEDIUM_MEM # define HASH_BITS 14 #endif #ifndef HASH_BITS # define HASH_BITS 15 /* For portability to 16 bit machines, do not use values above 15. */ #endif /* To save space (see unlzw.c), we overlay prev+head with tab_prefix and * window with tab_suffix. Check that we can do this: */ #if (WSIZE<<1) > (1<<BITS) error: cannot overlay window with tab_suffix and prev with tab_prefix0 #endif #if HASH_BITS > BITS-1 error: cannot overlay head with tab_prefix1 #endif #define HASH_SIZE (unsigned)(1<<HASH_BITS) #define HASH_MASK (HASH_SIZE-1) #define WMASK (WSIZE-1) /* HASH_SIZE and WSIZE must be powers of two */ #define NIL 0 /* Tail of hash chains */ #define FAST 4 #define SLOW 2 /* speed options for the general purpose bit flag */ #ifndef TOO_FAR # define TOO_FAR 4096 #endif /* Matches of length 3 are discarded if their distance exceeds TOO_FAR */ /* =========================================================================== * Local data used by the "longest match" routines. */ typedef ush Pos; typedef unsigned IPos; /* A Pos is an index in the character window. We use short instead of int to * save space in the various tables. IPos is used only for parameter passing. */ /* DECLARE(uch, window, 2L*WSIZE); */ /* Sliding window. Input bytes are read into the second half of the window, * and move to the first half later to keep a dictionary of at least WSIZE * bytes. With this organization, matches are limited to a distance of * WSIZE-MAX_MATCH bytes, but this ensures that IO is always * performed with a length multiple of the block size. Also, it limits * the window size to 64K, which is quite useful on MSDOS. * To do: limit the window size to WSIZE+BSZ if SMALL_MEM (the code would * be less efficient). */ /* DECLARE(Pos, prev, WSIZE); */ /* Link to older string with same hash index. To limit the size of this * array to 64K, this link is maintained only for the last 32K strings. * An index in this array is thus a window index modulo 32K. */ /* DECLARE(Pos, head, 1<<HASH_BITS); */ /* Heads of the hash chains or NIL. */ ulg window_size = (ulg)2*WSIZE; /* window size, 2*WSIZE except for MMAP or BIG_MEM, where it is the * input file length plus MIN_LOOKAHEAD. */ long block_start; /* window position at the beginning of the current output block. Gets * negative when the window is moved backwards. */ local unsigned ins_h; /* hash index of string to be inserted */ #define H_SHIFT ((HASH_BITS+MIN_MATCH-1)/MIN_MATCH) /* Number of bits by which ins_h and del_h must be shifted at each * input step. It must be such that after MIN_MATCH steps, the oldest * byte no longer takes part in the hash key, that is: * H_SHIFT * MIN_MATCH >= HASH_BITS */ unsigned int near prev_length; /* Length of the best match at previous step. Matches not greater than this * are discarded. This is used in the lazy match evaluation. */ unsigned near strstart; /* start of string to insert */ unsigned near match_start; /* start of matching string */ local int eofile; /* flag set at end of input file */ local unsigned lookahead; /* number of valid bytes ahead in window */ unsigned near max_chain_length; /* To speed up deflation, hash chains are never searched beyond this length. * A higher limit improves compression ratio but degrades the speed. */ local unsigned int max_lazy_match; /* Attempt to find a better match only when the current match is strictly * smaller than this value. This mechanism is used only for compression * levels >= 4. */ #define max_insert_length max_lazy_match /* Insert new strings in the hash table only if the match length * is not greater than this length. This saves time but degrades compression. * max_insert_length is used only for compression levels <= 3. */ local int compr_level; /* compression level (1..9) */ unsigned near good_match; /* Use a faster search when the previous match is longer than this */ /* Values for max_lazy_match, good_match and max_chain_length, depending on * the desired pack level (0..9). The values given below have been tuned to * exclude worst case performance for pathological files. Better values may be * found for specific files. */ typedef struct config { ush good_length; /* reduce lazy search above this match length */ ush max_lazy; /* do not perform lazy search above this match length */ ush nice_length; /* quit search above this match length */ ush max_chain; } config; #ifdef FULL_SEARCH # define nice_match MAX_MATCH #else int near nice_match; /* Stop searching when current match exceeds this */ #endif local config configuration_table[10] = { /* good lazy nice chain */ /* 0 */ {0, 0, 0, 0}, /* store only */ /* 1 */ {4, 4, 8, 4}, /* maximum speed, no lazy matches */ /* 2 */ {4, 5, 16, 8}, /* 3 */ {4, 6, 32, 32}, /* 4 */ {4, 4, 16, 16}, /* lazy matches */ /* 5 */ {8, 16, 32, 32}, /* 6 */ {8, 16, 128, 128}, /* 7 */ {8, 32, 128, 256}, /* 8 */ {32, 128, 258, 1024}, /* 9 */ {32, 258, 258, 4096}}; /* maximum compression */ /* Note: the deflate() code requires max_lazy >= MIN_MATCH and max_chain >= 4 * For deflate_fast() (levels <= 3) good is ignored and lazy has a different * meaning. */ #define EQUAL 0 /* result of memcmp for equal strings */ /* =========================================================================== * Prototypes for local functions. */ local void fill_window OF((void)); local ulg deflate_fast OF((void)); int longest_match OF((IPos cur_match)); #ifdef ASMV void match_init OF((void)); /* asm code initialization */ #endif #ifdef DEBUG local void check_match OF((IPos start, IPos match, int length)); #endif /* =========================================================================== * Update a hash value with the given input byte * IN assertion: all calls to to UPDATE_HASH are made with consecutive * input characters, so that a running hash key can be computed from the * previous key instead of complete recalculation each time. */ #define UPDATE_HASH(h,c) (h = (((h)<<H_SHIFT) ^ (c)) & HASH_MASK) /* =========================================================================== * Insert string s in the dictionary and set match_head to the previous head * of the hash chain (the most recent string with same hash key). Return * the previous length of the hash chain. * IN assertion: all calls to to INSERT_STRING are made with consecutive * input characters and the first MIN_MATCH bytes of s are valid * (except for the last MIN_MATCH-1 bytes of the input file). */ #define INSERT_STRING(s, match_head) \ (UPDATE_HASH(ins_h, window[(s) + MIN_MATCH-1]), \ prev[(s) & WMASK] = match_head = head[ins_h], \ head[ins_h] = (s)) /* =========================================================================== * Initialize the "longest match" routines for a new file */ void lm_init (pack_level, flags) int pack_level; /* 0: store, 1: best speed, 9: best compression */ ush *flags; /* general purpose bit flag */ { register unsigned j; if (pack_level < 1 || pack_level > 9) error("bad pack level"); compr_level = pack_level; /* Initialize the hash table. */ #if defined(MAXSEG_64K) && HASH_BITS == 15 for (j = 0; j < HASH_SIZE; j++) head[j] = NIL; #else memzero((char*)head, HASH_SIZE*sizeof(*head)); #endif /* prev will be initialized on the fly */ /* Set the default configuration parameters: */ max_lazy_match = configuration_table[pack_level].max_lazy; good_match = configuration_table[pack_level].good_length; #ifndef FULL_SEARCH nice_match = configuration_table[pack_level].nice_length; #endif max_chain_length = configuration_table[pack_level].max_chain; if (pack_level == 1) { *flags |= FAST; } else if (pack_level == 9) { *flags |= SLOW; } /* ??? reduce max_chain_length for binary files */ strstart = 0; block_start = 0L; #ifdef ASMV match_init(); /* initialize the asm code */ #endif lookahead = read_buf((char*)window, sizeof(int) <= 2 ? (unsigned)WSIZE : 2*WSIZE); if (lookahead == 0 || lookahead == (unsigned)EOF) { eofile = 1, lookahead = 0; return; } eofile = 0; /* Make sure that we always have enough lookahead. This is important * if input comes from a device such as a tty. */ while (lookahead < MIN_LOOKAHEAD && !eofile) fill_window(); ins_h = 0; for (j=0; j<MIN_MATCH-1; j++) UPDATE_HASH(ins_h, window[j]); /* If lookahead < MIN_MATCH, ins_h is garbage, but this is * not important since only literal bytes will be emitted. */ } /* =========================================================================== * Set match_start to the longest match starting at the given string and * return its length. Matches shorter or equal to prev_length are discarded, * in which case the result is equal to prev_length and match_start is * garbage. * IN assertions: cur_match is the head of the hash chain for the current * string (strstart) and its distance is <= MAX_DIST, and prev_length >= 1 */ #ifndef ASMV /* For MSDOS, OS/2 and 386 Unix, an optimized version is in match.asm or * match.s. The code is functionally equivalent, so you can use the C version * if desired. */ int longest_match(cur_match) IPos cur_match; /* current match */ { unsigned chain_length = max_chain_length; /* max hash chain length */ register uch *scan = window + strstart; /* current string */ register uch *match; /* matched string */ register int len; /* length of current match */ int best_len = prev_length; /* best match length so far */ IPos limit = strstart > (IPos)MAX_DIST ? strstart - (IPos)MAX_DIST : NIL; /* Stop when cur_match becomes <= limit. To simplify the code, * we prevent matches with the string of window index 0. */ /* The code is optimized for HASH_BITS >= 8 and MAX_MATCH-2 multiple of 16. * It is easy to get rid of this optimization if necessary. */ #if HASH_BITS < 8 || MAX_MATCH != 258 error: Code too clever #endif #ifdef UNALIGNED_OK /* Compare two bytes at a time. Note: this is not always beneficial. * Try with and without -DUNALIGNED_OK to check. */ register uch *strend = window + strstart + MAX_MATCH - 1; register ush scan_start = *(ush*)scan; register ush scan_end = *(ush*)(scan+best_len-1); #else register uch *strend = window + strstart + MAX_MATCH; register uch scan_end1 = scan[best_len-1]; register uch scan_end = scan[best_len]; #endif /* Do not waste too much time if we already have a good match: */ if (prev_length >= good_match) { chain_length >>= 2; } Assert(strstart <= window_size-MIN_LOOKAHEAD, "insufficient lookahead"); do { Assert(cur_match < strstart, "no future"); match = window + cur_match; /* Skip to next match if the match length cannot increase * or if the match length is less than 2: */ #if (defined(UNALIGNED_OK) && MAX_MATCH == 258) /* This code assumes sizeof(unsigned short) == 2. Do not use * UNALIGNED_OK if your compiler uses a different size. */ if (*(ush*)(match+best_len-1) != scan_end || *(ush*)match != scan_start) continue; /* It is not necessary to compare scan[2] and match[2] since they are * always equal when the other bytes match, given that the hash keys * are equal and that HASH_BITS >= 8. Compare 2 bytes at a time at * strstart+3, +5, ... up to strstart+257. We check for insufficient * lookahead only every 4th comparison; the 128th check will be made * at strstart+257. If MAX_MATCH-2 is not a multiple of 8, it is * necessary to put more guard bytes at the end of the window, or * to check more often for insufficient lookahead. */ scan++, match++; do { } while (*(ush*)(scan+=2) == *(ush*)(match+=2) && *(ush*)(scan+=2) == *(ush*)(match+=2) && *(ush*)(scan+=2) == *(ush*)(match+=2) && *(ush*)(scan+=2) == *(ush*)(match+=2) && scan < strend); /* The funny "do {}" generates better code on most compilers */ /* Here, scan <= window+strstart+257 */ Assert(scan <= window+(unsigned)(window_size-1), "wild scan"); if (*scan == *match) scan++; len = (MAX_MATCH - 1) - (int)(strend-scan); scan = strend - (MAX_MATCH-1); #else /* UNALIGNED_OK */ if (match[best_len] != scan_end || match[best_len-1] != scan_end1 || *match != *scan || *++match != scan[1]) continue; /* The check at best_len-1 can be removed because it will be made * again later. (This heuristic is not always a win.) * It is not necessary to compare scan[2] and match[2] since they * are always equal when the other bytes match, given that * the hash keys are equal and that HASH_BITS >= 8. */ scan += 2, match++; /* We check for insufficient lookahead only every 8th comparison; * the 256th check will be made at strstart+258. */ do { } while (*++scan == *++match && *++scan == *++match && *++scan == *++match && *++scan == *++match && *++scan == *++match && *++scan == *++match && *++scan == *++match && *++scan == *++match && scan < strend); len = MAX_MATCH - (int)(strend - scan); scan = strend - MAX_MATCH; #endif /* UNALIGNED_OK */ if (len > best_len) { match_start = cur_match; best_len = len; if (len >= nice_match) break; #ifdef UNALIGNED_OK scan_end = *(ush*)(scan+best_len-1); #else scan_end1 = scan[best_len-1]; scan_end = scan[best_len]; #endif } } while ((cur_match = prev[cur_match & WMASK]) > limit && --chain_length != 0); return best_len; } #endif /* ASMV */ #ifdef DEBUG /* =========================================================================== * Check that the match at match_start is indeed a match. */ local void check_match(start, match, length) IPos start, match; int length; { /* check that the match is indeed a match */ if (memcmp((char*)window + match, (char*)window + start, length) != EQUAL) { sprintf(strerr, " start %d, match %d, length %d; invalid match", start, match, length); error(strerr); } if (verbose > 1) { fprintf(stderr,"\\[%d,%d]", start-match, length); do { putc(window[start++], stderr); } while (--length != 0); } } #else # define check_match(start, match, length) #endif /* =========================================================================== * Fill the window when the lookahead becomes insufficient. * Updates strstart and lookahead, and sets eofile if end of input file. * IN assertion: lookahead < MIN_LOOKAHEAD && strstart + lookahead > 0 * OUT assertions: at least one byte has been read, or eofile is set; * file reads are performed for at least two bytes (required for the * translate_eol option). */ local void fill_window() { register unsigned n, m; unsigned more = (unsigned)(window_size - (ulg)lookahead - (ulg)strstart); /* Amount of free space at the end of the window. */ /* If the window is almost full and there is insufficient lookahead, * move the upper half to the lower one to make room in the upper half. */ if (more == (unsigned)EOF) { /* Very unlikely, but possible on 16 bit machine if strstart == 0 * and lookahead == 1 (input done one byte at time) */ more--; } else if (strstart >= WSIZE+MAX_DIST) { /* By the IN assertion, the window is not empty so we can't confuse * more == 0 with more == 64K on a 16 bit machine. */ Assert(window_size == (ulg)2*WSIZE, "no sliding with BIG_MEM"); memcpy((char*)window, (char*)window+WSIZE, (unsigned)WSIZE); match_start -= WSIZE; strstart -= WSIZE; /* we now have strstart >= MAX_DIST: */ block_start -= (long) WSIZE; for (n = 0; n < HASH_SIZE; n++) { m = head[n]; head[n] = (Pos)(m >= WSIZE ? m-WSIZE : NIL); } for (n = 0; n < WSIZE; n++) { m = prev[n]; nse. @item If the distribution and/or use of the Program is restricted in certain countries either by patents or by copyrighted interfaces, the original copyright holder who places the Program under this License may add an explicit geographical distribution limitation excluding those countries, so that distribution is permitted only in or among countries not thus excluded. In such case, this License incorporates the limitation as if written in the body of this License. @item The Free Software Foundation may publish revised and/or new versions of the General Public License from time to time. Such new versions will be similar in spirit to the present version, but may differ in detail to address new problems or concerns. Each version is given a distinguishing version number. If the Program specifies a version number of this License which applies to it and ``any later version'', you have the option of following the terms and conditions either of that version or of any later version published by the Free Software Foundation. If the Program does not specify a version number of this License, you may choose any version ever published by the Free Software Foundation. @item If you wish to incorporate parts of the Program into other free programs whose distribution conditions are different, write to the author to ask for permission. For software which is copyrighted by the Free Software Foundation, write to the Free Software Foundation; we sometimes make exceptions for this. Our decision will be guided by the two goals of preserving the free status of all derivatives of our free software and of promoting the sharing and reuse of software generally. @iftex @heading NO WARRANTY @end iftex @ifinfo @center NO WARRANTY @end ifinfo @item BECAUSE THE PROGRAM IS LICENSED FREE OF CHARGE, THERE IS NO WARRANTY FOR THE PROGRAM, TO THE EXTENT PERMITTED BY APPLICABLE LAW. EXCEPT WHEN OTHERWISE STATED IN WRITING THE COPYRIGHT HOLDERS AND/OR OTHER PARTIES PROVIDE THE PROGRAM ``AS IS'' WITHOUT WARRANTY OF ANY KIND, EITHER EXPREtself at the start of the input file). */ match_length = longest_match (hash_head); /* longest_match() sets match_start */ if (match_length > lookahead) match_length = lookahead; } if (match_length >= MIN_MATCH) { check_match(strstart, match_start, match_length); flush = ct_tally(strstart-match_start, match_length - MIN_MATCH); lookahead -= match_length; /* Insert new strings in the hash table only if the match length * is not too large. This saves time but degrades compression. */ if (match_length <= max_insert_length) { match_length--; /* string at strstart already in hash table */ do { strstart++; INSERT_STRING(strstart, hash_head); /* strstart never exceeds WSIZE-MAX_MATCH, so there are * always MIN_MATCH bytes ahead. If lookahead < MIN_MATCH * these bytes are garbage, but it does not matter since * the next lookahead bytes will be emitted as literals. */ } while (--match_length != 0); strstart++; } else { strstart += match_length; match_length = 0; ins_h = window[strstart]; UPDATE_HASH(ins_h, window[strstart+1]); #if MIN_MATCH != 3 Call UPDATE_HASH() MIN_MATCH-3 more times #endif } } else { /* No match, output a literal byte */ Tracevv((stderr,"%c",window[strstart])); flush = ct_tally (0, window[strstart]); lookahead--; strstart++; } if (flush) FLUSH_BLOCK(0), block_start = strstart; /* Make sure that we always have enough lookahead, except * at the end of the input file. We need MAX_MATCH bytes * for the next match, plus MIN_MATCH bytes to insert the * string following the next match. */ while (lookahead < MIN_LOOKAHEAD && !eofile) fill_window(); } return FLUSH_BLOCK(1); /* eof */ } /* =========================================================================== * Same as above, but achieves better compression. We use a lazy * evaluation for matches: a match is finally adopted only if there is * no better match at the next window position. */ ulg deflate() { IPos hash_head; /* head of hash chain */ IPos prev_match; /* previous match */ int flush; /* set if current block must be flushed */ int match_available = 0; /* set if previous match exists */ register unsigned match_length = MIN_MATCH-1; /* length of best match */ #ifdef DEBUG extern long isize; /* byte length of input file, for debug only */ #endif if (compr_level <= 3) return deflate_fast(); /* optimized for speed */ /* Process the input block. */ while (lookahead != 0) { /* Insert the string window[strstart .. strstart+2] in the * dictionary, and set hash_head to the head of the hash chain: */ INSERT_STRING(strstart, hash_head); /* Find the longest match, discarding those <= prev_length. */ prev_length = match_length, prev_match = match_start; match_length = MIN_MATCH-1; if (hash_head != NIL && prev_length < max_lazy_match && strstart - hash_head <= MAX_DIST) { /* To simplify the code, we prevent matches with the string * of window index 0 (in particular we have to avoid a match * of the string with itself at the start of the input file). */ match_length = longest_match (hash_head); /* longest_match() sets match_start */ if (match_length > lookahead) match_length = lookahead; /* Ignore a length 3 match if it is too distant: */ if (match_length == MIN_MATCH && strstart-match_start > TOO_FAR){ /* If prev_match is also MIN_MATCH, match_start is garbage * but we will ignore the current match anyway. */ match_length--; } } /* If there was a match at the previous step and the current * match is not better, output the previous match: */ if (prev_length >= MIN_MATCH && match_length <= prev_length) { check_match(strstart-1, prev_match, prev_length); flush = ct_tally(strstart-1-prev_match, prev_length - MIN_MATCH); /* Insert in hash table all strings up to the end of the match. * strstart-1 and strstart are already inserted. */ lookahead -= prev_length-1; prev_length -= 2; do { strstart++; INSERT_STRING(strstart, hash_head); /* strstart never exceeds WSIZE-MAX_MATCH, so there are * always MIN_MATCH bytes ahead. If lookahead < MIN_MATCH * these bytes are garbage, but it does not matter since the * next lookahead bytes will always be emitted as literals. */ } while (--prev_length != 0); match_available = 0; match_length = MIN_MATCH-1; strstart++; if (flush) FLUSH_BLOCK(0), block_start = strstart; } else if (match_available) { /* If there was no match at the previous position, output a * single literal. If there was a match but the current match * is longer, truncate the previous match to a single literal. */ Tracevv((stderr,"%c",window[strstart-1])); if (ct_tally (0, window[strstart-1])) { FLUSH_BLOCK(0), block_start = strstart; } strstart++; lookahead--; } else { /* There is no previous match to compare with, wait for * the next step to decide. */ match_available = 1; strstart++; lookahead--; } Assert (strstart <= isize && lookahead <= isize, "a bit too far"); /* Make sure that we always have enough lookahead, except * at the end of the input file. We need MAX_MATCH bytes * for the next match, plus MIN_MATCH bytes to insert the * string following the next match. */ while (lookahead < MIN_LOOKAHEAD && !eofile) fill_window(); } if (match_available) ct_tally (0, window[strstart-1]); return FLUSH_BLOCK(1); /* eof */ }