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Diffstat (limited to 'deflate.c')
| -rw-r--r-- | deflate.c | 852 |
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diff --git a/deflate.c b/deflate.c new file mode 100644 index 0000000..6e235f3 --- /dev/null +++ b/deflate.c @@ -0,0 +1,852 @@ +/* deflate.c -- compress data using the deflation algorithm + + Copyright (C) 1999, 2006, 2009-2016 Free Software Foundation, Inc. + Copyright (C) 1992-1993 Jean-loup Gailly + + This program is free software; you can redistribute it and/or modify + it under the terms of the GNU General Public License as published by + the Free Software Foundation; either version 3, or (at your option) + any later version. + + This program is distributed in the hope that it will be useful, + but WITHOUT ANY WARRANTY; without even the implied warranty of + MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the + GNU General Public License for more details. + + You should have received a copy of the GNU General Public License + along with this program; if not, write to the Free Software Foundation, + Inc., 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301, USA. */ + +/* + * 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 + * + * off_t deflate (void) + * Processes a new input file and return its compressed length. Sets + * the compressed length, crc, deflate flags and internal file + * attributes. + */ + +#include <config.h> +#include <stdio.h> + +#include "tailor.h" +#include "gzip.h" +#include "lzw.h" /* just for consistency checking */ +#include "verify.h" + +/* =========================================================================== + * 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 */ + +#ifndef RSYNC_WIN +# define RSYNC_WIN 4096 +#endif +verify(RSYNC_WIN < MAX_DIST); + +#define RSYNC_SUM_MATCH(sum) ((sum) % RSYNC_WIN == 0) +/* Whether window sum matches magic value */ + +/* =========================================================================== + * 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. */ + +static 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 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 good_match; +/* Use a faster search when the previous match is longer than this */ + +local ulg rsync_sum; /* rolling sum of rsync window */ +local ulg rsync_chunk_end; /* next rsync sequence point */ + +/* 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 ASMV +# define static_unless_ASMV +#else +# define static_unless_ASMV static +#endif + +#ifdef FULL_SEARCH +# define nice_match MAX_MATCH +#else + /* Stop searching when current match exceeds this */ + static_unless_ASMV int nice_match; +#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. + */ + +/* =========================================================================== + * Prototypes for local functions. + */ +local void fill_window (void); +local off_t deflate_fast (void); + +#ifdef ASMV + int longest_match (IPos cur_match); + void match_init (void); /* asm code initialization */ +#endif + +#ifdef DEBUG +local void check_match (IPos start, IPos match, int length); +#endif + +/* =========================================================================== + * Update a hash value with the given input byte + * IN assertion: all calls 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 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) gzip_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 */ + + /* rsync params */ + rsync_chunk_end = 0xFFFFFFFFUL; + rsync_sum = 0; + + /* 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. + */ +static int +longest_match(IPos cur_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) != 0) { + fprintf(stderr, + " start %d, match %d, length %d\n", + start, match, length); + gzip_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: */ + if (rsync_chunk_end != 0xFFFFFFFFUL) + rsync_chunk_end -= WSIZE; + + 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; + /* Don't let garbage pollute the dictionary. */ + memzero (window + strstart + lookahead, MIN_MATCH - 1); + } else { + lookahead += n; + } + } +} + +/* With an initial offset of START, advance rsync's rolling checksum + by NUM bytes. */ +local void rsync_roll(unsigned int start, unsigned int num) +{ + unsigned i; + + if (start < RSYNC_WIN) { + /* before window fills. */ + for (i = start; i < RSYNC_WIN; i++) { + if (i == start + num) + return; + rsync_sum += (ulg)window[i]; + } + num -= (RSYNC_WIN - start); + start = RSYNC_WIN; + } + + /* buffer after window full */ + for (i = start; i < start+num; i++) { + /* New character in */ + rsync_sum += (ulg)window[i]; + /* Old character out */ + rsync_sum -= (ulg)window[i - RSYNC_WIN]; + if (rsync_chunk_end == 0xFFFFFFFFUL && RSYNC_SUM_MATCH(rsync_sum)) + rsync_chunk_end = i; + } +} + +/* =========================================================================== + * Set rsync_chunk_end if window sum matches magic value. + */ +#define RSYNC_ROLL(s, n) \ + do { if (rsync) rsync_roll((s), (n)); } while(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(eof) \ + flush_block(block_start >= 0L ? (char*)&window[(unsigned)block_start] : \ + (char*)NULL, (long)strstart - block_start, flush-1, (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 off_t deflate_fast() +{ + IPos hash_head; /* head of the hash chain */ + int flush = 0; /* set if current block must be flushed, 2=>and padded */ + 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 + && strstart <= window_size - MIN_LOOKAHEAD) { + /* 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; + + RSYNC_ROLL(strstart, 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]); + RSYNC_ROLL(strstart, 1); + lookahead--; + strstart++; + } + if (rsync && strstart > rsync_chunk_end) { + rsync_chunk_end = 0xFFFFFFFFUL; + flush = 2; + } + 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. + */ +off_t deflate() +{ + IPos hash_head; /* head of hash chain */ + IPos prev_match; /* previous match */ + int flush = 0; /* 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 */ + + 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 && + strstart <= window_size - MIN_LOOKAHEAD) { + /* 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; + RSYNC_ROLL(strstart, prev_length+1); + 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 (rsync && strstart > rsync_chunk_end) { + rsync_chunk_end = 0xFFFFFFFFUL; + flush = 2; + } + 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])); + flush = ct_tally (0, window[strstart-1]); + if (rsync && strstart > rsync_chunk_end) { + rsync_chunk_end = 0xFFFFFFFFUL; + flush = 2; + } + if (flush) FLUSH_BLOCK(0), block_start = strstart; + RSYNC_ROLL(strstart, 1); + strstart++; + lookahead--; + } else { + /* There is no previous match to compare with, wait for + * the next step to decide. + */ + if (rsync && strstart > rsync_chunk_end) { + /* Reset huffman tree */ + rsync_chunk_end = 0xFFFFFFFFUL; + flush = 2; + FLUSH_BLOCK(0), block_start = strstart; + } + + match_available = 1; + RSYNC_ROLL(strstart, 1); + strstart++; + lookahead--; + } + Assert (strstart <= bytes_in && lookahead <= bytes_in, "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 */ +} |