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Diffstat (limited to 'deflate.c')
| -rw-r--r-- | deflate.c | 929 |
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diff --git a/deflate.c b/deflate.c new file mode 100644 index 0000000..c830854 --- /dev/null +++ b/deflate.c @@ -0,0 +1,929 @@ +/* + deflate.c - Zip 3 + + Copyright (c) 1990-2007 Info-ZIP. All rights reserved. + + See the accompanying file LICENSE, version 2005-Feb-10 or later + (the contents of which are also included in zip.h) for terms of use. + If, for some reason, all these files are missing, the Info-ZIP license + also may be found at: ftp://ftp.info-zip.org/pub/infozip/license.html +*/ +/* + * deflate.c by Jean-loup Gailly. + * + * 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. + */ + +#define __DEFLATE_C + +#include "zip.h" + +#ifndef USE_ZLIB + +/* =========================================================================== + * 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 + +#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 */ + +#if (defined(ASMV) && !defined(MSDOS16) && defined(DYN_ALLOC)) + error: DYN_ALLOC not yet supported in match.S or match32.asm +#endif + +#ifdef MEMORY16 +# define MAXSEG_64K +#endif + +/* =========================================================================== + * Local data used by the "longest match" routines. + */ + +#if defined(MMAP) || defined(BIG_MEM) + typedef unsigned Pos; /* must be at least 32 bits */ +#else + typedef ush Pos; +#endif +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. + */ + +#ifndef DYN_ALLOC + 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+CBSZ if SMALL_MEM (the code would + * be less efficient since the data would have to be copied WSIZE/CBSZ times) + */ + 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. + */ + Pos head[HASH_SIZE]; + /* Heads of the hash chains or NIL. If your compiler thinks that + * HASH_SIZE is a dynamic value, recompile with -DDYN_ALLOC. + */ +#else + uch far * near window = NULL; + Pos far * near prev = NULL; + Pos far * near head; +#endif +ulg window_size; +/* 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 int sliding; +/* Set to false when the input file is already in memory */ + +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. + */ + +unsigned near good_match; +/* Use a faster search when the previous match is longer than this */ + +#ifdef FULL_SEARCH +# define nice_match MAX_MATCH +#else + int near nice_match; /* Stop searching when current match exceeds this */ +#endif + + +/* Values for max_lazy_match, good_match, nice_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; + +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 uzoff_t deflate_fast OF((void)); /* now use uzoff_t 7/24/04 EG */ + + int longest_match OF((IPos cur_match)); +#if defined(ASMV) && !defined(RISCOS) + 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 + * + * IN assertion: window_size is > 0 if the input file is already read or + * mmap'ed in the window[] array, 0 otherwise. In the first case, + * window_size is sufficient to contain the whole input file plus + * MIN_LOOKAHEAD bytes (to avoid referencing memory beyond the end + * of window[] when looking for matches towards the end). + */ +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"); + + /* Do not slide the window if the whole input is already in memory + * (window_size > 0) + */ + sliding = 0; + if (window_size == 0L) { + sliding = 1; + window_size = (ulg)2L*WSIZE; + } + + /* Use dynamic allocation if compiler does not like big static arrays: */ +#ifdef DYN_ALLOC + if (window == NULL) { + window = (uch far *) zcalloc(WSIZE, 2*sizeof(uch)); + if (window == NULL) ziperr(ZE_MEM, "window allocation"); + } + if (prev == NULL) { + prev = (Pos far *) zcalloc(WSIZE, sizeof(Pos)); + head = (Pos far *) zcalloc(HASH_SIZE, sizeof(Pos)); + if (prev == NULL || head == NULL) { + ziperr(ZE_MEM, "hash table allocation"); + } + } +#endif /* DYN_ALLOC */ + + /* Initialize the hash table (avoiding 64K overflow for 16 bit systems). + * prev[] will be initialized on the fly. + */ + head[HASH_SIZE-1] = NIL; + memset((char*)head, NIL, (unsigned)(HASH_SIZE-1)*sizeof(*head)); + + /* 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 <= 2) { + *flags |= FAST; + } else if (pack_level >= 8) { + *flags |= SLOW; + } + /* ??? reduce max_chain_length for binary files */ + + strstart = 0; + block_start = 0L; +#if defined(ASMV) && !defined(RISCOS) + match_init(); /* initialize the asm code */ +#endif + + j = WSIZE; +#ifndef MAXSEG_64K + if (sizeof(int) > 2) j <<= 1; /* Can read 64K in one step */ +#endif + lookahead = (*read_buf)((char*)window, j); + + 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. + */ + if (lookahead < MIN_LOOKAHEAD) 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. + */ +} + +/* =========================================================================== + * Free the window and hash table + */ +void lm_free() +{ +#ifdef DYN_ALLOC + if (window != NULL) { + zcfree(window); + window = NULL; + } + if (prev != NULL) { + zcfree(prev); + zcfree(head); + prev = head = NULL; + } +#endif /* DYN_ALLOC */ +} + +/* =========================================================================== + * 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 and ARM, 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 far *scan = window + strstart; /* current string */ + register uch far *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 far *strend = window + strstart + MAX_MATCH - 1; + register ush scan_start = *(ush far *)scan; + register ush scan_end = *(ush far *)(scan+best_len-1); +#else + register uch far *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 far *)(match+best_len-1) != scan_end || + *(ush far *)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 far *)(scan+=2) == *(ush far *)(match+=2) && + *(ush far *)(scan+=2) == *(ush far *)(match+=2) && + *(ush far *)(scan+=2) == *(ush far *)(match+=2) && + *(ush far *)(scan+=2) == *(ush far *)(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); + + Assert(scan <= window+(unsigned)(window_size-1), "wild scan"); + + 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 far *)(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(mesg, + " start %d, match %d, length %d\n", + start, match, length); + error("invalid match"); + } + if (verbose > 1) { + fprintf(mesg,"\\[%d,%d]", start-match, length); +#ifndef WINDLL + do { putc(window[start++], mesg); } while (--length != 0); +#else + do { fprintf(stdout,"%c",window[start++]); } while (--length != 0); +#endif + } +} +#else +# define check_match(start, match, length) +#endif + +/* =========================================================================== + * 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, (ulg)strstart - (ulg)block_start, (eof)) + +/* =========================================================================== + * 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: strstart <= window_size-MIN_LOOKAHEAD + * 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; /* Amount of free space at the end of the window. */ + + do { + more = (unsigned)(window_size - (ulg)lookahead - (ulg)strstart); + + /* 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--; + + /* For MMAP or BIG_MEM, the whole input file is already in memory so + * we must not perform sliding. We must however call (*read_buf)() in + * order to compute the crc, update lookahead and possibly set eofile. + */ + } else if (strstart >= WSIZE+MAX_DIST && sliding) { + +#ifdef FORCE_METHOD + /* When methods "stored" or "store_block" are requested, the + * current block must be flushed before sliding the window. + */ + if (level <= 2) FLUSH_BLOCK(0), block_start = strstart; +#endif + /* 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*)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; + if (dot_size > 0 && !display_globaldots) { + /* initial space */ + if (noisy && dot_count == -1) { +#ifndef WINDLL + putc(' ', mesg); + fflush(mesg); +#else + fprintf(stdout,"%c",' '); +#endif + dot_count++; + } + dot_count++; + if (dot_size <= (dot_count + 1) * WSIZE) dot_count = 0; + } + if ((verbose || noisy) && dot_size && !dot_count) { +#ifndef WINDLL + putc('.', mesg); + fflush(mesg); +#else + fprintf(stdout,"%c",'.'); +#endif + mesg_line_started = 1; + } + } + if (eofile) 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 MMAP or BIG_MEM case (not yet supported in gzip), + * window_size == input_size + MIN_LOOKAHEAD && + * strstart + 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)((char*)window+strstart+lookahead, more); + if (n == 0 || n == (unsigned)EOF) { + eofile = 1; + } else { + lookahead += n; + } + } while (lookahead < MIN_LOOKAHEAD && !eofile); +} + +/* =========================================================================== + * Processes a new input file and return its compressed length. This + * function does not perform lazy evaluation of 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 uzoff_t deflate_fast() +{ + IPos hash_head = NIL; /* 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: + */ +#ifndef DEFL_UNDETERM + if (lookahead >= MIN_MATCH) +#endif + 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). + */ +#ifndef HUFFMAN_ONLY +# ifndef DEFL_UNDETERM + /* Do not look for matches beyond the end of the input. + * This is necessary to make deflate deterministic. + */ + if ((unsigned)nice_match > lookahead) nice_match = (int)lookahead; +# endif + match_length = longest_match (hash_head); + /* longest_match() sets match_start */ + if (match_length > lookahead) match_length = lookahead; +#endif + } + 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 +#ifndef DEFL_UNDETERM + && lookahead >= MIN_MATCH +#endif + ) { + 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. + */ +#ifdef DEFL_UNDETERM + /* If lookahead < MIN_MATCH these bytes are garbage, + * but it does not matter since the next lookahead bytes + * will be emitted as literals. + */ +#endif + } 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. + */ + if (lookahead < MIN_LOOKAHEAD) 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. + */ +uzoff_t deflate() +{ + IPos hash_head = NIL; /* 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 uzoff_t isize; /* byte length of input file, for debug only */ +#endif + + if (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: + */ +#ifndef DEFL_UNDETERM + if (lookahead >= MIN_MATCH) +#endif + 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). + */ +#ifndef HUFFMAN_ONLY +# ifndef DEFL_UNDETERM + /* Do not look for matches beyond the end of the input. + * This is necessary to make deflate deterministic. + */ + if ((unsigned)nice_match > lookahead) nice_match = (int)lookahead; +# endif + match_length = longest_match (hash_head); + /* longest_match() sets match_start */ + if (match_length > lookahead) match_length = lookahead; +#endif + +#ifdef FILTERED + /* Ignore matches of length <= 5 */ + if (match_length <= 5) { +#else + /* Ignore a length 3 match if it is too distant: */ + if (match_length == MIN_MATCH && strstart-match_start > TOO_FAR){ +#endif + /* If prev_match is also MIN_MATCH, match_start is garbage + * but we will ignore the current match anyway. + */ + 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 (prev_length >= MIN_MATCH && match_length <= prev_length) { +#ifndef DEFL_UNDETERM + unsigned max_insert = strstart + lookahead - MIN_MATCH; + +#endif + 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; +#ifndef DEFL_UNDETERM + do { + if (++strstart <= max_insert) { + INSERT_STRING(strstart, hash_head); + /* strstart never exceeds WSIZE-MAX_MATCH, so there are + * always MIN_MATCH bytes ahead. + */ + } + } while (--prev_length != 0); + strstart++; +#else /* DEFL_UNDETERM */ + 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); + strstart++; +#endif /* ?DEFL_UNDETERM */ + match_available = 0; + match_length = MIN_MATCH-1; + + 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. + */ + if (lookahead < MIN_LOOKAHEAD) fill_window(); + } + if (match_available) ct_tally (0, window[strstart-1]); + + return FLUSH_BLOCK(1); /* eof */ +} +#endif /* !USE_ZLIB */ |