diff options
Diffstat (limited to 'gnu/usr.bin/gzip/deflate.c')
| -rw-r--r-- | gnu/usr.bin/gzip/deflate.c | 763 |
1 files changed, 0 insertions, 763 deletions
diff --git a/gnu/usr.bin/gzip/deflate.c b/gnu/usr.bin/gzip/deflate.c deleted file mode 100644 index cbc4884..0000000 --- a/gnu/usr.bin/gzip/deflate.c +++ /dev/null @@ -1,763 +0,0 @@ -/* 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. - */ - -/* - * 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[] = "$FreeBSD$"; -#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) { - fprintf(stderr, - " start %d, match %d, length %d\n", - start, match, length); - error("invalid match"); - } - 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]; - prev[n] = (Pos)(m >= WSIZE ? m-WSIZE : NIL); - /* If n is not on any hash chain, prev[n] is garbage but - * its value will never be used. - */ - } - more += WSIZE; - } - /* At this point, more >= 2 */ - if (!eofile) { - n = read_buf((char*)window+strstart+lookahead, more); - if (n == 0 || n == (unsigned)EOF) { - eofile = 1; - } else { - lookahead += n; - } - } -} - -/* =========================================================================== - * Flush the current block, with given end-of-file flag. - * IN assertion: strstart is set to the end of the current match. - */ -#define FLUSH_BLOCK(eof) \ - flush_block(block_start >= 0L ? (char*)&window[(unsigned)block_start] : \ - (char*)NULL, (long)strstart - block_start, (eof)) - -/* =========================================================================== - * Processes a new input file and return its compressed length. This - * function does not perform lazy evaluationof matches and inserts - * new strings in the dictionary only for unmatched strings or for short - * matches. It is used only for the fast compression options. - */ -local ulg deflate_fast() -{ - IPos hash_head; /* head of the hash chain */ - int flush; /* set if current block must be flushed */ - unsigned match_length = 0; /* length of best match */ - - prev_length = MIN_MATCH-1; - 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. - * At this point we have always match_length < MIN_MATCH - */ - if (hash_head != NIL && 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; - } - 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 */ -} |
