/* deflate.c -- compress data using the deflation algorithm * Copyright (C) 1995 Jean-loup Gailly. * For conditions of distribution and use, see copyright notice in zlib.h */ /* * ALGORITHM * * 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 people for bug reports and testing. * * REFERENCES * * Deutsch, L.P.,"'Deflate' Compressed Data Format Specification". * Available in ftp.uu.net:/pub/archiving/zip/doc/deflate-1.1.doc * * 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 * */ /* $Id: deflate.c,v 1.3 1995/04/10 16:03:45 jloup Exp $ */ #include "deflate.h" char copyright[] = " deflate Copyright 1995 Jean-loup Gailly "; /* If you use the zlib library in a product, an acknowledgment is welcome in the documentation of your product. If for some reason you cannot include such an acknowledgment, I would appreciate that you keep this copyright string in the executable of your product. */ #define NIL 0 /* Tail of hash chains */ #ifndef TOO_FAR # define TOO_FAR 4096 #endif /* Matches of length 3 are discarded if their distance exceeds TOO_FAR */ #define MIN_LOOKAHEAD (MAX_MATCH+MIN_MATCH+1) /* Minimum amount of lookahead, except at the end of the input file. * See deflate.c for comments about the MIN_MATCH+1. */ /* 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_s { 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; 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 */ struct static_tree_desc_s {int dummy;}; /* for buggy compilers */ /* =========================================================================== * Prototypes for local functions. */ local void fill_window __P((deflate_state *s)); local int deflate_fast __P((deflate_state *s, int flush)); local int deflate_slow __P((deflate_state *s, int flush)); local void lm_init __P((deflate_state *s)); local int longest_match __P((deflate_state *s, IPos cur_match)); #ifdef ASMV void match_init __P((void)); /* asm code initialization */ #endif #ifdef DEBUG local void check_match __P((deflate_state *s, 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(s,h,c) (h = (((h)<hash_shift) ^ (c)) & s->hash_mask) /* =========================================================================== * Insert string str 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 str are valid * (except for the last MIN_MATCH-1 bytes of the input file). */ #define INSERT_STRING(s, str, match_head) \ (UPDATE_HASH(s, s->ins_h, s->window[(str) + MIN_MATCH-1]), \ s->prev[(str) & s->w_mask] = match_head = s->head[s->ins_h], \ s->head[s->ins_h] = (str)) /* ========================================================================= */ int deflateInit (strm, level) z_stream *strm; int level; { return deflateInit2 (strm, level, DEFLATED, WBITS, MEM_LEVEL, 0); /* To do: ignore strm->next_in if we use it as window */ } /* ========================================================================= */ int deflateInit2 (strm, level, method, windowBits, memLevel, strategy) z_stream *strm; int level; int method; int windowBits; int memLevel; int strategy; { deflate_state *s; int noheader = 0; if (strm == Z_NULL) return Z_STREAM_ERROR; strm->msg = Z_NULL; if (strm->zalloc == Z_NULL) strm->zalloc = zcalloc; if (strm->zfree == Z_NULL) strm->zfree = zcfree; if (level == Z_DEFAULT_COMPRESSION) level = 6; if (windowBits < 0) { /* undocumented feature: suppress zlib header */ noheader = 1; windowBits = -windowBits; } if (memLevel < 1 || memLevel > MAX_MEM_LEVEL || method != DEFLATED || windowBits < 8 || windowBits > 15 || level < 1 || level > 9) { return Z_STREAM_ERROR; } s = (deflate_state *) ZALLOC(strm, 1, sizeof(deflate_state)); if (s == Z_NULL) return Z_MEM_ERROR; strm->state = (struct internal_state *)s; s->strm = strm; s->noheader = noheader; s->w_bits = windowBits; s->w_size = 1 << s->w_bits; s->hash_bits = memLevel + 7; s->hash_size = 1 << s->hash_bits; s->hash_shift = ((s->hash_bits+MIN_MATCH-1)/MIN_MATCH); s->window = (Byte*) ZALLOC(strm, s->w_size, 2*sizeof(Byte)); s->prev = (Pos*) ZALLOC(strm, s->w_size, sizeof(Pos)); s->head = (Pos*) ZALLOC(strm, s->hash_size, sizeof(Pos)); s->lit_bufsize = 1 << (memLevel + 6); /* 16K elements by default */ s->pending_buf = (uch*) ZALLOC(strm, s->lit_bufsize, 2*sizeof(ush)); if (s->window == Z_NULL || s->prev == Z_NULL || s->head == Z_NULL || s->pending_buf == Z_NULL) { strm->msg = z_errmsg[1-Z_MEM_ERROR]; deflateEnd (strm); return Z_MEM_ERROR; } s->d_buf = (ush*) &(s->pending_buf[s->lit_bufsize]); s->l_buf = (uch*) &(s->pending_buf[3*s->lit_bufsize]); /* We overlay pending_buf and d_buf+l_buf. This works since the average * output size for (length,distance) codes is <= 32 bits (worst case * is 15+15+13=33). */ s->level = level; s->strategy = strategy; s->method = method; return deflateReset(strm); } /* ========================================================================= */ int deflateReset (strm) z_stream *strm; { deflate_state *s; if (strm == Z_NULL || strm->state == Z_NULL || strm->zalloc == Z_NULL || strm->zfree == Z_NULL) return Z_STREAM_ERROR; strm->total_in = strm->total_out = 0; strm->msg = Z_NULL; /* use zfree if we ever allocate msg dynamically */ strm->data_type = Z_UNKNOWN; s = (deflate_state *)strm->state; s->pending = 0; s->pending_out = s->pending_buf; s->status = s->noheader ? BUSY_STATE : INIT_STATE; s->adler = 1; ct_init(s); lm_init(s); return Z_OK; } /* ========================================================================= * Put a short the pending_out buffer. The 16-bit value is put in MSB order. * IN assertion: the stream state is correct and there is enough room in * the pending_out buffer. */ local void putShortMSB (s, b) deflate_state *s; uInt b; { put_byte(s, b >> 8); put_byte(s, b & 0xff); } /* ========================================================================= * Flush as much pending output as possible. */ local void flush_pending(strm) z_stream *strm; { unsigned len = strm->state->pending; if (len > strm->avail_out) len = strm->avail_out; if (len == 0) return; zmemcpy(strm->next_out, strm->state->pending_out, len); strm->next_out += len; strm->state->pending_out += len; strm->total_out += len; strm->avail_out -= len; strm->state->pending -= len; if (strm->state->pending == 0) { strm->state->pending_out = strm->state->pending_buf; } } /* ========================================================================= */ int deflate (strm, flush) z_stream *strm; int flush; { if (strm == Z_NULL || strm->state == Z_NULL) return Z_STREAM_ERROR; if (strm->next_out == Z_NULL || strm->next_in == Z_NULL) { ERR_RETURN(strm, Z_STREAM_ERROR); } if (strm->avail_out == 0) ERR_RETURN(strm, Z_BUF_ERROR); strm->state->strm = strm; /* just in case */ /* Write the zlib header */ if (strm->state->status == INIT_STATE) { uInt header = (DEFLATED + ((strm->state->w_bits-8)<<4)) << 8; uInt level_flags = (strm->state->level-1) >> 1; if (level_flags > 3) level_flags = 3; header |= (level_flags << 6); header += 31 - (header % 31); strm->state->status = BUSY_STATE; putShortMSB(strm->state, header); } /* Flush as much pending output as possible */ if (strm->state->pending != 0) { flush_pending(strm); if (strm->avail_out == 0) return Z_OK; } /* User must not provide more input after the first FINISH: */ if (strm->state->status == FINISH_STATE && strm->avail_in != 0) { ERR_RETURN(strm, Z_BUF_ERROR); } /* Start a new block or continue the current one. */ if (strm->avail_in != 0 || (flush == Z_FINISH && strm->state->status != FINISH_STATE)) { if (flush == Z_FINISH) { strm->state->status = FINISH_STATE; } if (strm->state->level <= 3) { if (deflate_fast(strm->state, flush)) return Z_OK; } else { if (deflate_slow(strm->state, flush)) return Z_OK; } } Assert(strm->avail_out > 0, "bug2"); if (flush != Z_FINISH || strm->state->noheader) return Z_OK; /* Write the zlib trailer (adler32) */ putShortMSB(strm->state, strm->state->adler >> 16); putShortMSB(strm->state, strm->state->adler & 0xffff); flush_pending(strm); /* If avail_out is zero, the application will call deflate again * to flush the rest. */ strm->state->noheader = 1; /* write the trailer only once! */ return Z_OK; } /* ========================================================================= */ int deflateEnd (strm) z_stream *strm; { if (strm == Z_NULL || strm->state == Z_NULL) return Z_STREAM_ERROR; TRY_FREE(strm, strm->state->window); TRY_FREE(strm, strm->state->prev); TRY_FREE(strm, strm->state->head); TRY_FREE(strm, strm->state->pending_buf); ZFREE(strm, strm->state); strm->state = Z_NULL; return Z_OK; } /* ========================================================================= */ int deflateCopy (dest, source) z_stream *dest; z_stream *source; { if (source == Z_NULL || dest == Z_NULL || source->state == Z_NULL) { return Z_STREAM_ERROR; } *dest = *source; return Z_STREAM_ERROR; /* to be implemented */ #if 0 dest->state = (struct internal_state *) (*dest->zalloc)(1, sizeof(deflate_state)); if (dest->state == Z_NULL) return Z_MEM_ERROR; *(dest->state) = *(source->state); return Z_OK; #endif } /* =========================================================================== * Read a new buffer from the current input stream, update the adler32 * and total number of bytes read. */ local int read_buf(strm, buf, size) z_stream *strm; char *buf; unsigned size; { unsigned len = strm->avail_in; if (len > size) len = size; if (len == 0) return 0; strm->avail_in -= len; if (!strm->state->noheader) { strm->state->adler = adler32(strm->state->adler, strm->next_in, len); } zmemcpy(buf, strm->next_in, len); strm->next_in += len; strm->total_in += len; return (int)len; } /* =========================================================================== * Initialize the "longest match" routines for a new zlib stream */ local void lm_init (s) deflate_state *s; { register unsigned j; s->window_size = (ulg)2L*s->w_size; /* Initialize the hash table (avoiding 64K overflow for 16 bit systems). * prev[] will be initialized on the fly. */ s->head[s->hash_size-1] = NIL; zmemzero((char*)s->head, (unsigned)(s->hash_size-1)*sizeof(*s->head)); /* Set the default configuration parameters: */ s->max_lazy_match = configuration_table[s->level].max_lazy; s->good_match = configuration_table[s->level].good_length; s->nice_match = configuration_table[s->level].nice_length; s->max_chain_length = configuration_table[s->level].max_chain; s->strstart = 0; s->block_start = 0L; s->lookahead = 0; s->match_length = MIN_MATCH-1; s->match_available = 0; #ifdef ASMV match_init(); /* initialize the asm code */ #endif s->ins_h = 0; for (j=0; jins_h, s->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 80x86 and 680x0, an optimized version will be provided in match.asm or * match.S. The code will be functionally equivalent. */ local int longest_match(s, cur_match) deflate_state *s; IPos cur_match; /* current match */ { unsigned chain_length = s->max_chain_length;/* max hash chain length */ register Byte *scan = s->window + s->strstart; /* current string */ register Byte *match; /* matched string */ register int len; /* length of current match */ int best_len = s->prev_length; /* best match length so far */ IPos limit = s->strstart > (IPos)MAX_DIST(s) ? s->strstart - (IPos)MAX_DIST(s) : NIL; /* Stop when cur_match becomes <= limit. To simplify the code, * we prevent matches with the string of window index 0. */ #ifdef UNALIGNED_OK /* Compare two bytes at a time. Note: this is not always beneficial. * Try with and without -DUNALIGNED_OK to check. */ register Byte *strend = s->window + s->strstart + MAX_MATCH - 1; register ush scan_start = *(ush*)scan; register ush scan_end = *(ush*)(scan+best_len-1); #else register Byte *strend = s->window + s->strstart + MAX_MATCH; register Byte scan_end1 = scan[best_len-1]; register Byte scan_end = scan[best_len]; #endif /* 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. */ Assert(s->hash_bits >= 8 && MAX_MATCH == 258, "Code too clever"); /* Do not waste too much time if we already have a good match: */ if (s->prev_length >= s->good_match) { chain_length >>= 2; } Assert(s->strstart <= s->window_size-MIN_LOOKAHEAD, "need lookahead"); do { Assert(cur_match < s->strstart, "no future"); match = s->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 <= s->window+(unsigned)(s->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); Assert(scan <= s->window+(unsigned)(s->window_size-1), "wild scan"); len = MAX_MATCH - (int)(strend - scan); scan = strend - MAX_MATCH; #endif /* UNALIGNED_OK */ if (len > best_len) { s->match_start = cur_match; best_len = len; if (len >= s->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 = s->prev[cur_match & s->w_mask]) > 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(s, start, match, length) deflate_state *s; IPos start, match; int length; { /* check that the match is indeed a match */ if (memcmp((char*)s->window + match, (char*)s->window + start, length) != EQUAL) { fprintf(stderr, " start %d, match %d, length %d\n", start, match, length); z_error("invalid match"); } if (verbose > 1) { fprintf(stderr,"\\[%d,%d]", start-match, length); do { putc(s->window[start++], stderr); } while (--length != 0); } } #else # define check_match(s, start, match, length) #endif /* =========================================================================== * Fill the window when the lookahead becomes insufficient. * Updates strstart and lookahead. * * IN assertion: lookahead < MIN_LOOKAHEAD * OUT assertions: strstart <= window_size-MIN_LOOKAHEAD * At least one byte has been read, or avail_in == 0; reads are * performed for at least two bytes (required for the zip translate_eol * option -- not supported here). */ local void fill_window(s) deflate_state *s; { register unsigned n, m; unsigned more; /* Amount of free space at the end of the window. */ do { more = (unsigned)(s->window_size -(ulg)s->lookahead -(ulg)s->strstart); /* Deal with !@#$% 64K limit: */ if (more == 0 && s->strstart == 0 && s->lookahead == 0) { more = s->w_size; } else if (more == (unsigned)(-1)) { /* Very unlikely, but possible on 16 bit machine if strstart == 0 * and lookahead == 1 (input done one byte at time) */ more--; /* 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. */ } else if (s->strstart >= s->w_size+MAX_DIST(s)) { /* By the IN assertion, the window is not empty so we can't confuse * more == 0 with more == 64K on a 16 bit machine. */ memcpy((char*)s->window, (char*)s->window+s->w_size, (unsigned)s->w_size); s->match_start -= s->w_size; s->strstart -= s->w_size; /* we now have strstart >= MAX_DIST */ s->block_start -= (long) s->w_size; for (n = 0; n < s->hash_size; n++) { m = s->head[n]; s->head[n] = (Pos)(m >= s->w_size ? m-s->w_size : NIL); } for (n = 0; n < s->w_size; n++) { m = s->prev[n]; s->prev[n] = (Pos)(m >= s->w_size ? m-s->w_size : NIL); /* If n is not on any hash chain, prev[n] is garbage but * its value will never be used. */ } more += s->w_size; } if (s->strm->avail_in == 0) return; /* If there was no sliding: * strstart <= WSIZE+MAX_DIST-1 && lookahead <= MIN_LOOKAHEAD - 1 && * more == window_size - lookahead - strstart * => more >= window_size - (MIN_LOOKAHEAD-1 + WSIZE + MAX_DIST-1) * => more >= window_size - 2*WSIZE + 2 * In the BIG_MEM or MMAP case (not yet supported), * window_size == input_size + MIN_LOOKAHEAD && * strstart + s->lookahead <= input_size => more >= MIN_LOOKAHEAD. * Otherwise, window_size == 2*WSIZE so more >= 2. * If there was sliding, more >= WSIZE. So in all cases, more >= 2. */ Assert(more >= 2, "more < 2"); n = read_buf(s->strm, (char*)s->window + s->strstart + s->lookahead, more); s->lookahead += n; } while (s->lookahead < MIN_LOOKAHEAD && s->strm->avail_in != 0); } /* =========================================================================== * 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_ONLY(s, eof) { \ ct_flush_block(s, (s->block_start >= 0L ? \ (char*)&s->window[(unsigned)s->block_start] : \ (char*)Z_NULL), (long)s->strstart - s->block_start, (eof)); \ s->block_start = s->strstart; \ flush_pending(s->strm); \ } /* Same but force premature exit if necessary. */ #define FLUSH_BLOCK(s, eof) { \ FLUSH_BLOCK_ONLY(s, eof); \ if (s->strm->avail_out == 0) return 1; \ } /* =========================================================================== * Compress as much as possible from the input stream, return true if * processing was terminated prematurely (no more input or output space). * 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 int deflate_fast(s, flush) deflate_state *s; int flush; { IPos hash_head; /* head of the hash chain */ int bflush; /* set if current block must be flushed */ s->prev_length = MIN_MATCH-1; for (;;) { /* 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. */ if (s->lookahead < MIN_LOOKAHEAD) { fill_window(s); if (s->lookahead < MIN_LOOKAHEAD && flush == Z_NO_FLUSH) return 1; if (s->lookahead == 0) break; /* flush the current block */ } /* Insert the string window[strstart .. strstart+2] in the * dictionary, and set hash_head to the head of the hash chain: */ INSERT_STRING(s, s->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 && s->strstart - hash_head <= MAX_DIST(s)) { /* 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). */ if (s->strategy != Z_HUFFMAN_ONLY) { s->match_length = longest_match (s, hash_head); } /* longest_match() sets match_start */ if (s->match_length > s->lookahead) s->match_length = s->lookahead; } if (s->match_length >= MIN_MATCH) { check_match(s, s->strstart, s->match_start, s->match_length); bflush = ct_tally(s, s->strstart - s->match_start, s->match_length - MIN_MATCH); s->lookahead -= s->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 (s->match_length <= s->max_insert_length) { s->match_length--; /* string at strstart already in hash table */ do { s->strstart++; INSERT_STRING(s, s->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 (--s->match_length != 0); s->strstart++; } else { s->strstart += s->match_length; s->match_length = 0; s->ins_h = s->window[s->strstart]; UPDATE_HASH(s, s->ins_h, s->window[s->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", s->window[s->strstart])); bflush = ct_tally (s, 0, s->window[s->strstart]); s->lookahead--; s->strstart++; } if (bflush) FLUSH_BLOCK(s, 0); } FLUSH_BLOCK(s, flush == Z_FINISH); return 0; /* normal exit */ } /* =========================================================================== * 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. */ local int deflate_slow(s, flush) deflate_state *s; int flush; { IPos hash_head; /* head of hash chain */ int bflush; /* set if current block must be flushed */ /* Process the input block. */ for (;;) { /* 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. */ if (s->lookahead < MIN_LOOKAHEAD) { fill_window(s); if (s->lookahead < MIN_LOOKAHEAD && flush == Z_NO_FLUSH) return 1; if (s->lookahead == 0) break; /* flush the current block */ } /* Insert the string window[strstart .. strstart+2] in the * dictionary, and set hash_head to the head of the hash chain: */ INSERT_STRING(s, s->strstart, hash_head); /* Find the longest match, discarding those <= prev_length. */ s->prev_length = s->match_length, s->prev_match = s->match_start; s->match_length = MIN_MATCH-1; if (hash_head != NIL && s->prev_length < s->max_lazy_match && s->strstart - hash_head <= MAX_DIST(s)) { /* 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). */ if (s->strategy != Z_HUFFMAN_ONLY) { s->match_length = longest_match (s, hash_head); } /* longest_match() sets match_start */ if (s->match_length > s->lookahead) s->match_length = s->lookahead; if (s->match_length <= 5 && (s->strategy == Z_FILTERED || (s->match_length == MIN_MATCH && s->strstart - s->match_start > TOO_FAR))) { /* If prev_match is also MIN_MATCH, match_start is garbage * but we will ignore the current match anyway. */ s->match_length = MIN_MATCH-1; } } /* If there was a match at the previous step and the current * match is not better, output the previous match: */ if (s->prev_length >= MIN_MATCH && s->match_length <= s->prev_length) { check_match(s, s->strstart-1, s->prev_match, s->prev_length); bflush = ct_tally(s, s->strstart -1 - s->prev_match, s->prev_length - MIN_MATCH); /* Insert in hash table all strings up to the end of the match. * strstart-1 and strstart are already inserted. */ s->lookahead -= s->prev_length-1; s->prev_length -= 2; do { s->strstart++; INSERT_STRING(s, s->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 (--s->prev_length != 0); s->match_available = 0; s->match_length = MIN_MATCH-1; s->strstart++; if (bflush) FLUSH_BLOCK(s, 0); } else if (s->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", s->window[s->strstart-1])); if (ct_tally (s, 0, s->window[s->strstart-1])) { FLUSH_BLOCK_ONLY(s, 0); } s->strstart++; s->lookahead--; if (s->strm->avail_out == 0) return 1; } else { /* There is no previous match to compare with, wait for * the next step to decide. */ s->match_available = 1; s->strstart++; s->lookahead--; } } if (s->match_available) ct_tally (s, 0, s->window[s->strstart-1]); FLUSH_BLOCK(s, flush == Z_FINISH); return 0; }