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zlib/deflate.c

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/* 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 1.6 1995/05/01 17:23:57 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));
local void putShortMSB __P((deflate_state *s, uInt b));
local void flush_pending __P((z_stream *strm));
local int read_buf __P((z_stream *strm, char *buf, unsigned size));
#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)<<s->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))
/* ===========================================================================
* Initialize the hash table (avoiding 64K overflow for 16 bit systems).
* prev[] will be initialized on the fly.
*/
#define CLEAR_HASH(s) \
s->head[s->hash_size-1] = NIL; \
zmemzero((char*)s->head, (unsigned)(s->hash_size-1)*sizeof(*s->head));
/* ========================================================================= */
int deflateInit (strm, level)
z_stream *strm;
int level;
{
return deflateInit2 (strm, level, DEFLATED, MAX_WBITS, MAX_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->w_mask = s->w_size - 1;
s->hash_bits = memLevel + 7;
s->hash_size = 1 << s->hash_bits;
s->hash_mask = s->hash_size - 1;
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 = (Byte)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, (Byte)(b >> 8));
put_byte(s, (Byte)(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;
}
/* ??? remember Z_FULL_FLUSH if we didn't have enough space */
if (flush == Z_FULL_FLUSH) {
ct_stored_block(strm->state, (char*)0, 0L, 0); /* special marker */
flush_pending(strm);
CLEAR_HASH(strm->state); /* forget history */
if (strm->avail_out == 0) return Z_OK;
}
}
Assert(strm->avail_out > 0, "bug2");
if (flush != Z_FINISH) return Z_OK;
if (strm->state->noheader) return Z_STREAM_END;
/* Write the zlib trailer (adler32) */
putShortMSB(strm->state, (uInt)(strm->state->adler >> 16));
putShortMSB(strm->state, (uInt)(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 strm->state->pending != 0 ? Z_OK : Z_STREAM_END;
}
/* ========================================================================= */
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;
CLEAR_HASH(s);
/* 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; j<MIN_MATCH-1; j++) UPDATE_HASH(s, s->ins_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]);
s->match_available = 0;
}
FLUSH_BLOCK(s, flush == Z_FINISH);
return 0;
}