764 lines
28 KiB
C
764 lines
28 KiB
C
/* 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[] = "$Id: deflate.c,v 1.2 1993/10/15 23:05:30 jtc Exp $";
|
|
#endif
|
|
|
|
/* ===========================================================================
|
|
* Configuration parameters
|
|
*/
|
|
|
|
/* Compile with MEDIUM_MEM to reduce the memory requirements or
|
|
* with SMALL_MEM to use as little memory as possible. Use BIG_MEM if the
|
|
* entire input file can be held in memory (not possible on 16 bit systems).
|
|
* Warning: defining these symbols affects HASH_BITS (see below) and thus
|
|
* affects the compression ratio. The compressed output
|
|
* is still correct, and might even be smaller in some cases.
|
|
*/
|
|
|
|
#ifdef SMALL_MEM
|
|
# define HASH_BITS 13 /* Number of bits used to hash strings */
|
|
#endif
|
|
#ifdef MEDIUM_MEM
|
|
# define HASH_BITS 14
|
|
#endif
|
|
#ifndef HASH_BITS
|
|
# define HASH_BITS 15
|
|
/* For portability to 16 bit machines, do not use values above 15. */
|
|
#endif
|
|
|
|
/* To save space (see unlzw.c), we overlay prev+head with tab_prefix and
|
|
* window with tab_suffix. Check that we can do this:
|
|
*/
|
|
#if (WSIZE<<1) > (1<<BITS)
|
|
error: cannot overlay window with tab_suffix and prev with tab_prefix0
|
|
#endif
|
|
#if HASH_BITS > BITS-1
|
|
error: cannot overlay head with tab_prefix1
|
|
#endif
|
|
|
|
#define HASH_SIZE (unsigned)(1<<HASH_BITS)
|
|
#define HASH_MASK (HASH_SIZE-1)
|
|
#define WMASK (WSIZE-1)
|
|
/* HASH_SIZE and WSIZE must be powers of two */
|
|
|
|
#define NIL 0
|
|
/* Tail of hash chains */
|
|
|
|
#define FAST 4
|
|
#define SLOW 2
|
|
/* speed options for the general purpose bit flag */
|
|
|
|
#ifndef TOO_FAR
|
|
# define TOO_FAR 4096
|
|
#endif
|
|
/* Matches of length 3 are discarded if their distance exceeds TOO_FAR */
|
|
|
|
/* ===========================================================================
|
|
* Local data used by the "longest match" routines.
|
|
*/
|
|
|
|
typedef ush Pos;
|
|
typedef unsigned IPos;
|
|
/* A Pos is an index in the character window. We use short instead of int to
|
|
* save space in the various tables. IPos is used only for parameter passing.
|
|
*/
|
|
|
|
/* DECLARE(uch, window, 2L*WSIZE); */
|
|
/* Sliding window. Input bytes are read into the second half of the window,
|
|
* and move to the first half later to keep a dictionary of at least WSIZE
|
|
* bytes. With this organization, matches are limited to a distance of
|
|
* WSIZE-MAX_MATCH bytes, but this ensures that IO is always
|
|
* performed with a length multiple of the block size. Also, it limits
|
|
* the window size to 64K, which is quite useful on MSDOS.
|
|
* To do: limit the window size to WSIZE+BSZ if SMALL_MEM (the code would
|
|
* be less efficient).
|
|
*/
|
|
|
|
/* DECLARE(Pos, prev, WSIZE); */
|
|
/* Link to older string with same hash index. To limit the size of this
|
|
* array to 64K, this link is maintained only for the last 32K strings.
|
|
* An index in this array is thus a window index modulo 32K.
|
|
*/
|
|
|
|
/* DECLARE(Pos, head, 1<<HASH_BITS); */
|
|
/* Heads of the hash chains or NIL. */
|
|
|
|
ulg window_size = (ulg)2*WSIZE;
|
|
/* window size, 2*WSIZE except for MMAP or BIG_MEM, where it is the
|
|
* input file length plus MIN_LOOKAHEAD.
|
|
*/
|
|
|
|
long block_start;
|
|
/* window position at the beginning of the current output block. Gets
|
|
* negative when the window is moved backwards.
|
|
*/
|
|
|
|
local unsigned ins_h; /* hash index of string to be inserted */
|
|
|
|
#define H_SHIFT ((HASH_BITS+MIN_MATCH-1)/MIN_MATCH)
|
|
/* Number of bits by which ins_h and del_h must be shifted at each
|
|
* input step. It must be such that after MIN_MATCH steps, the oldest
|
|
* byte no longer takes part in the hash key, that is:
|
|
* H_SHIFT * MIN_MATCH >= HASH_BITS
|
|
*/
|
|
|
|
unsigned int near prev_length;
|
|
/* Length of the best match at previous step. Matches not greater than this
|
|
* are discarded. This is used in the lazy match evaluation.
|
|
*/
|
|
|
|
unsigned near strstart; /* start of string to insert */
|
|
unsigned near match_start; /* start of matching string */
|
|
local int eofile; /* flag set at end of input file */
|
|
local unsigned lookahead; /* number of valid bytes ahead in window */
|
|
|
|
unsigned near max_chain_length;
|
|
/* To speed up deflation, hash chains are never searched beyond this length.
|
|
* A higher limit improves compression ratio but degrades the speed.
|
|
*/
|
|
|
|
local unsigned int max_lazy_match;
|
|
/* Attempt to find a better match only when the current match is strictly
|
|
* smaller than this value. This mechanism is used only for compression
|
|
* levels >= 4.
|
|
*/
|
|
#define max_insert_length max_lazy_match
|
|
/* Insert new strings in the hash table only if the match length
|
|
* is not greater than this length. This saves time but degrades compression.
|
|
* max_insert_length is used only for compression levels <= 3.
|
|
*/
|
|
|
|
local int compr_level;
|
|
/* compression level (1..9) */
|
|
|
|
unsigned near good_match;
|
|
/* Use a faster search when the previous match is longer than this */
|
|
|
|
|
|
/* Values for max_lazy_match, good_match and max_chain_length, depending on
|
|
* the desired pack level (0..9). The values given below have been tuned to
|
|
* exclude worst case performance for pathological files. Better values may be
|
|
* found for specific files.
|
|
*/
|
|
|
|
typedef struct config {
|
|
ush good_length; /* reduce lazy search above this match length */
|
|
ush max_lazy; /* do not perform lazy search above this match length */
|
|
ush nice_length; /* quit search above this match length */
|
|
ush max_chain;
|
|
} config;
|
|
|
|
#ifdef FULL_SEARCH
|
|
# define nice_match MAX_MATCH
|
|
#else
|
|
int near nice_match; /* Stop searching when current match exceeds this */
|
|
#endif
|
|
|
|
local config configuration_table[10] = {
|
|
/* good lazy nice chain */
|
|
/* 0 */ {0, 0, 0, 0}, /* store only */
|
|
/* 1 */ {4, 4, 8, 4}, /* maximum speed, no lazy matches */
|
|
/* 2 */ {4, 5, 16, 8},
|
|
/* 3 */ {4, 6, 32, 32},
|
|
|
|
/* 4 */ {4, 4, 16, 16}, /* lazy matches */
|
|
/* 5 */ {8, 16, 32, 32},
|
|
/* 6 */ {8, 16, 128, 128},
|
|
/* 7 */ {8, 32, 128, 256},
|
|
/* 8 */ {32, 128, 258, 1024},
|
|
/* 9 */ {32, 258, 258, 4096}}; /* maximum compression */
|
|
|
|
/* Note: the deflate() code requires max_lazy >= MIN_MATCH and max_chain >= 4
|
|
* For deflate_fast() (levels <= 3) good is ignored and lazy has a different
|
|
* meaning.
|
|
*/
|
|
|
|
#define EQUAL 0
|
|
/* result of memcmp for equal strings */
|
|
|
|
/* ===========================================================================
|
|
* Prototypes for local functions.
|
|
*/
|
|
local void fill_window OF((void));
|
|
local ulg deflate_fast OF((void));
|
|
|
|
int longest_match OF((IPos cur_match));
|
|
#ifdef ASMV
|
|
void match_init OF((void)); /* asm code initialization */
|
|
#endif
|
|
|
|
#ifdef DEBUG
|
|
local void check_match OF((IPos start, IPos match, int length));
|
|
#endif
|
|
|
|
/* ===========================================================================
|
|
* Update a hash value with the given input byte
|
|
* IN assertion: all calls to to UPDATE_HASH are made with consecutive
|
|
* input characters, so that a running hash key can be computed from the
|
|
* previous key instead of complete recalculation each time.
|
|
*/
|
|
#define UPDATE_HASH(h,c) (h = (((h)<<H_SHIFT) ^ (c)) & HASH_MASK)
|
|
|
|
/* ===========================================================================
|
|
* Insert string s in the dictionary and set match_head to the previous head
|
|
* of the hash chain (the most recent string with same hash key). Return
|
|
* the previous length of the hash chain.
|
|
* IN assertion: all calls to to INSERT_STRING are made with consecutive
|
|
* input characters and the first MIN_MATCH bytes of s are valid
|
|
* (except for the last MIN_MATCH-1 bytes of the input file).
|
|
*/
|
|
#define INSERT_STRING(s, match_head) \
|
|
(UPDATE_HASH(ins_h, window[(s) + MIN_MATCH-1]), \
|
|
prev[(s) & WMASK] = match_head = head[ins_h], \
|
|
head[ins_h] = (s))
|
|
|
|
/* ===========================================================================
|
|
* Initialize the "longest match" routines for a new file
|
|
*/
|
|
void lm_init (pack_level, flags)
|
|
int pack_level; /* 0: store, 1: best speed, 9: best compression */
|
|
ush *flags; /* general purpose bit flag */
|
|
{
|
|
register unsigned j;
|
|
|
|
if (pack_level < 1 || pack_level > 9) error("bad pack level");
|
|
compr_level = pack_level;
|
|
|
|
/* Initialize the hash table. */
|
|
#if defined(MAXSEG_64K) && HASH_BITS == 15
|
|
for (j = 0; j < HASH_SIZE; j++) head[j] = NIL;
|
|
#else
|
|
memzero((char*)head, HASH_SIZE*sizeof(*head));
|
|
#endif
|
|
/* prev will be initialized on the fly */
|
|
|
|
/* Set the default configuration parameters:
|
|
*/
|
|
max_lazy_match = configuration_table[pack_level].max_lazy;
|
|
good_match = configuration_table[pack_level].good_length;
|
|
#ifndef FULL_SEARCH
|
|
nice_match = configuration_table[pack_level].nice_length;
|
|
#endif
|
|
max_chain_length = configuration_table[pack_level].max_chain;
|
|
if (pack_level == 1) {
|
|
*flags |= FAST;
|
|
} else if (pack_level == 9) {
|
|
*flags |= SLOW;
|
|
}
|
|
/* ??? reduce max_chain_length for binary files */
|
|
|
|
strstart = 0;
|
|
block_start = 0L;
|
|
#ifdef ASMV
|
|
match_init(); /* initialize the asm code */
|
|
#endif
|
|
|
|
lookahead = read_buf((char*)window,
|
|
sizeof(int) <= 2 ? (unsigned)WSIZE : 2*WSIZE);
|
|
|
|
if (lookahead == 0 || lookahead == (unsigned)EOF) {
|
|
eofile = 1, lookahead = 0;
|
|
return;
|
|
}
|
|
eofile = 0;
|
|
/* Make sure that we always have enough lookahead. This is important
|
|
* if input comes from a device such as a tty.
|
|
*/
|
|
while (lookahead < MIN_LOOKAHEAD && !eofile) fill_window();
|
|
|
|
ins_h = 0;
|
|
for (j=0; j<MIN_MATCH-1; j++) UPDATE_HASH(ins_h, window[j]);
|
|
/* If lookahead < MIN_MATCH, ins_h is garbage, but this is
|
|
* not important since only literal bytes will be emitted.
|
|
*/
|
|
}
|
|
|
|
/* ===========================================================================
|
|
* Set match_start to the longest match starting at the given string and
|
|
* return its length. Matches shorter or equal to prev_length are discarded,
|
|
* in which case the result is equal to prev_length and match_start is
|
|
* garbage.
|
|
* IN assertions: cur_match is the head of the hash chain for the current
|
|
* string (strstart) and its distance is <= MAX_DIST, and prev_length >= 1
|
|
*/
|
|
#ifndef ASMV
|
|
/* For MSDOS, OS/2 and 386 Unix, an optimized version is in match.asm or
|
|
* match.s. The code is functionally equivalent, so you can use the C version
|
|
* if desired.
|
|
*/
|
|
int longest_match(cur_match)
|
|
IPos cur_match; /* current match */
|
|
{
|
|
unsigned chain_length = max_chain_length; /* max hash chain length */
|
|
register uch *scan = window + strstart; /* current string */
|
|
register uch *match; /* matched string */
|
|
register int len; /* length of current match */
|
|
int best_len = prev_length; /* best match length so far */
|
|
IPos limit = strstart > (IPos)MAX_DIST ? strstart - (IPos)MAX_DIST : NIL;
|
|
/* Stop when cur_match becomes <= limit. To simplify the code,
|
|
* we prevent matches with the string of window index 0.
|
|
*/
|
|
|
|
/* The code is optimized for HASH_BITS >= 8 and MAX_MATCH-2 multiple of 16.
|
|
* It is easy to get rid of this optimization if necessary.
|
|
*/
|
|
#if HASH_BITS < 8 || MAX_MATCH != 258
|
|
error: Code too clever
|
|
#endif
|
|
|
|
#ifdef UNALIGNED_OK
|
|
/* Compare two bytes at a time. Note: this is not always beneficial.
|
|
* Try with and without -DUNALIGNED_OK to check.
|
|
*/
|
|
register uch *strend = window + strstart + MAX_MATCH - 1;
|
|
register ush scan_start = *(ush*)scan;
|
|
register ush scan_end = *(ush*)(scan+best_len-1);
|
|
#else
|
|
register uch *strend = window + strstart + MAX_MATCH;
|
|
register uch scan_end1 = scan[best_len-1];
|
|
register uch scan_end = scan[best_len];
|
|
#endif
|
|
|
|
/* Do not waste too much time if we already have a good match: */
|
|
if (prev_length >= good_match) {
|
|
chain_length >>= 2;
|
|
}
|
|
Assert(strstart <= window_size-MIN_LOOKAHEAD, "insufficient lookahead");
|
|
|
|
do {
|
|
Assert(cur_match < strstart, "no future");
|
|
match = window + cur_match;
|
|
|
|
/* Skip to next match if the match length cannot increase
|
|
* or if the match length is less than 2:
|
|
*/
|
|
#if (defined(UNALIGNED_OK) && MAX_MATCH == 258)
|
|
/* This code assumes sizeof(unsigned short) == 2. Do not use
|
|
* UNALIGNED_OK if your compiler uses a different size.
|
|
*/
|
|
if (*(ush*)(match+best_len-1) != scan_end ||
|
|
*(ush*)match != scan_start) continue;
|
|
|
|
/* It is not necessary to compare scan[2] and match[2] since they are
|
|
* always equal when the other bytes match, given that the hash keys
|
|
* are equal and that HASH_BITS >= 8. Compare 2 bytes at a time at
|
|
* strstart+3, +5, ... up to strstart+257. We check for insufficient
|
|
* lookahead only every 4th comparison; the 128th check will be made
|
|
* at strstart+257. If MAX_MATCH-2 is not a multiple of 8, it is
|
|
* necessary to put more guard bytes at the end of the window, or
|
|
* to check more often for insufficient lookahead.
|
|
*/
|
|
scan++, match++;
|
|
do {
|
|
} while (*(ush*)(scan+=2) == *(ush*)(match+=2) &&
|
|
*(ush*)(scan+=2) == *(ush*)(match+=2) &&
|
|
*(ush*)(scan+=2) == *(ush*)(match+=2) &&
|
|
*(ush*)(scan+=2) == *(ush*)(match+=2) &&
|
|
scan < strend);
|
|
/* The funny "do {}" generates better code on most compilers */
|
|
|
|
/* Here, scan <= window+strstart+257 */
|
|
Assert(scan <= window+(unsigned)(window_size-1), "wild scan");
|
|
if (*scan == *match) scan++;
|
|
|
|
len = (MAX_MATCH - 1) - (int)(strend-scan);
|
|
scan = strend - (MAX_MATCH-1);
|
|
|
|
#else /* UNALIGNED_OK */
|
|
|
|
if (match[best_len] != scan_end ||
|
|
match[best_len-1] != scan_end1 ||
|
|
*match != *scan ||
|
|
*++match != scan[1]) continue;
|
|
|
|
/* The check at best_len-1 can be removed because it will be made
|
|
* again later. (This heuristic is not always a win.)
|
|
* It is not necessary to compare scan[2] and match[2] since they
|
|
* are always equal when the other bytes match, given that
|
|
* the hash keys are equal and that HASH_BITS >= 8.
|
|
*/
|
|
scan += 2, match++;
|
|
|
|
/* We check for insufficient lookahead only every 8th comparison;
|
|
* the 256th check will be made at strstart+258.
|
|
*/
|
|
do {
|
|
} while (*++scan == *++match && *++scan == *++match &&
|
|
*++scan == *++match && *++scan == *++match &&
|
|
*++scan == *++match && *++scan == *++match &&
|
|
*++scan == *++match && *++scan == *++match &&
|
|
scan < strend);
|
|
|
|
len = MAX_MATCH - (int)(strend - scan);
|
|
scan = strend - MAX_MATCH;
|
|
|
|
#endif /* UNALIGNED_OK */
|
|
|
|
if (len > best_len) {
|
|
match_start = cur_match;
|
|
best_len = len;
|
|
if (len >= nice_match) break;
|
|
#ifdef UNALIGNED_OK
|
|
scan_end = *(ush*)(scan+best_len-1);
|
|
#else
|
|
scan_end1 = scan[best_len-1];
|
|
scan_end = scan[best_len];
|
|
#endif
|
|
}
|
|
} while ((cur_match = prev[cur_match & WMASK]) > limit
|
|
&& --chain_length != 0);
|
|
|
|
return best_len;
|
|
}
|
|
#endif /* ASMV */
|
|
|
|
#ifdef DEBUG
|
|
/* ===========================================================================
|
|
* Check that the match at match_start is indeed a match.
|
|
*/
|
|
local void check_match(start, match, length)
|
|
IPos start, match;
|
|
int length;
|
|
{
|
|
/* check that the match is indeed a match */
|
|
if (memcmp((char*)window + match,
|
|
(char*)window + start, length) != EQUAL) {
|
|
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 */
|
|
}
|