/* +++ deflate.c */ /* deflate.c -- compress data using the deflation algorithm * Copyright (C) 1995-1996 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://ds.internic.net/rfc/rfc1951.txt * * 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 *
*/
/* =========================================================================== * Local data
*/
#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.
*/
/* Workspace to be allocated for deflate processing */ typedefstruct deflate_workspace { /* State memory for the deflator */
deflate_state deflate_memory; #ifdef CONFIG_ZLIB_DFLTCC /* State memory for s390 hardware deflate */ struct dfltcc_deflate_state dfltcc_memory; #endif
Byte *window_memory;
Pos *prev_memory;
Pos *head_memory; char *overlay_memory;
} deflate_workspace;
#ifdef CONFIG_ZLIB_DFLTCC /* dfltcc_state must be doubleword aligned for DFLTCC call */
static_assert(offsetof(struct deflate_workspace, dfltcc_memory) % 8 == 0); #endif
/* 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.
*/ typedefstruct 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;
compress_func func;
} config;
/* 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.
*/
/* =========================================================================== * 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(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 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] = (Pos)(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; \
memset((char *)s->head, 0, (unsigned)(s->hash_size-1)*sizeof(*s->head));
/* ========================================================================= */ int zlib_deflateInit2(
z_streamp strm, int level, int method, int windowBits, int memLevel, int strategy
)
{
deflate_state *s; int noheader = 0;
deflate_workspace *mem; char *next;
ush *overlay; /* We overlay pending_buf and d_buf+l_buf. This works since the average * output size for (length,distance) codes is <= 24 bits.
*/
/* * Direct the workspace's pointers to the chunks that were allocated * along with the deflate_workspace struct.
*/
next = (char *) mem;
next += sizeof(*mem); #ifdef CONFIG_ZLIB_DFLTCC /* * DFLTCC requires the window to be page aligned. * Thus, we overallocate and take the aligned portion of the buffer.
*/
mem->window_memory = (Byte *) PTR_ALIGN(next, PAGE_SIZE); #else
mem->window_memory = (Byte *) next; #endif
next += zlib_deflate_window_memsize(windowBits);
mem->prev_memory = (Pos *) next;
next += zlib_deflate_prev_memsize(windowBits);
mem->head_memory = (Pos *) next;
next += zlib_deflate_head_memsize(memLevel);
mem->overlay_memory = next;
s = (deflate_state *)strm->state;
s->pending = 0;
s->pending_out = s->pending_buf;
if (s->noheader < 0) {
s->noheader = 0; /* was set to -1 by deflate(..., Z_FINISH); */
}
s->status = s->noheader ? BUSY_STATE : INIT_STATE;
strm->adler = 1;
s->last_flush = Z_NO_FLUSH;
zlib_tr_init(s);
lm_init(s);
DEFLATE_RESET_HOOK(strm);
return Z_OK;
}
/* ========================================================================= * Put a short in the pending buffer. The 16-bit value is put in MSB order. * IN assertion: the stream state is correct and there is enough room in * pending_buf.
*/ staticvoid putShortMSB(
deflate_state *s,
uInt b
)
{
put_byte(s, (Byte)(b >> 8));
put_byte(s, (Byte)(b & 0xff));
}
/* ========================================================================= */ int zlib_deflate(
z_streamp strm, int flush
)
{ int old_flush; /* value of flush param for previous deflate call */
deflate_state *s;
/* Save the adler32 of the preset dictionary: */ if (s->strstart != 0) {
putShortMSB(s, (uInt)(strm->adler >> 16));
putShortMSB(s, (uInt)(strm->adler & 0xffff));
}
strm->adler = 1L;
}
/* Flush as much pending output as possible */ if (s->pending != 0) {
flush_pending(strm); if (strm->avail_out == 0) { /* Since avail_out is 0, deflate will be called again with * more output space, but possibly with both pending and * avail_in equal to zero. There won't be anything to do, * but this is not an error situation so make sure we * return OK instead of BUF_ERROR at next call of deflate:
*/
s->last_flush = -1; return Z_OK;
}
/* Make sure there is something to do and avoid duplicate consecutive * flushes. For repeated and useless calls with Z_FINISH, we keep * returning Z_STREAM_END instead of Z_BUFF_ERROR.
*/
} elseif (strm->avail_in == 0 && flush <= old_flush &&
flush != Z_FINISH) { return Z_BUF_ERROR;
}
/* User must not provide more input after the first FINISH: */ if (s->status == FINISH_STATE && strm->avail_in != 0) { return Z_BUF_ERROR;
}
/* Start a new block or continue the current one.
*/ if (strm->avail_in != 0 || s->lookahead != 0 ||
(flush != Z_NO_FLUSH && s->status != FINISH_STATE)) {
block_state bstate;
if (bstate == finish_started || bstate == finish_done) {
s->status = FINISH_STATE;
} if (bstate == need_more || bstate == finish_started) { if (strm->avail_out == 0) {
s->last_flush = -1; /* avoid BUF_ERROR next call, see above */
} return Z_OK; /* If flush != Z_NO_FLUSH && avail_out == 0, the next call * of deflate should use the same flush parameter to make sure * that the flush is complete. So we don't have to output an * empty block here, this will be done at next call. This also * ensures that for a very small output buffer, we emit at most * one empty block.
*/
} if (bstate == block_done) { if (flush == Z_PARTIAL_FLUSH) {
zlib_tr_align(s);
} elseif (flush == Z_PACKET_FLUSH) { /* Output just the 3-bit `stored' block type value,
but not a zero length. */
zlib_tr_stored_type_only(s);
} else { /* FULL_FLUSH or SYNC_FLUSH */
zlib_tr_stored_block(s, (char*)0, 0L, 0); /* For a full flush, this empty block will be recognized * as a special marker by inflate_sync().
*/ if (flush == Z_FULL_FLUSH) {
CLEAR_HASH(s); /* forget history */
}
}
flush_pending(strm); if (strm->avail_out == 0) {
s->last_flush = -1; /* avoid BUF_ERROR at next call, see above */ return Z_OK;
}
}
}
Assert(strm->avail_out > 0, "bug2");
if (flush != Z_FINISH) return Z_OK;
if (!s->noheader) { /* Write zlib trailer (adler32) */
putShortMSB(s, (uInt)(strm->adler >> 16));
putShortMSB(s, (uInt)(strm->adler & 0xffff));
}
flush_pending(strm); /* If avail_out is zero, the application will call deflate again * to flush the rest.
*/ if (!s->noheader) {
s->noheader = -1; /* write the trailer only once! */
} if (s->pending == 0) {
Assert(s->bi_valid == 0, "bi_buf not flushed"); return Z_STREAM_END;
} return Z_OK;
}
/* ========================================================================= */ int zlib_deflateEnd(
z_streamp strm
)
{ int status;
deflate_state *s;
if (strm == NULL || strm->state == NULL) return Z_STREAM_ERROR;
s = (deflate_state *) strm->state;
status = s->status; if (status != INIT_STATE && status != BUSY_STATE &&
status != FINISH_STATE) { return Z_STREAM_ERROR;
}
strm->state = NULL;
return status == BUSY_STATE ? Z_DATA_ERROR : Z_OK;
}
/* =========================================================================== * Read a new buffer from the current input stream, update the adler32 * and total number of bytes read. All deflate() input goes through * this function so some applications may wish to modify it to avoid * allocating a large strm->next_in buffer and copying from it. * (See also flush_pending()).
*/ staticint read_buf(
z_streamp strm,
Byte *buf, unsigned size
)
{ unsigned len = strm->avail_in;
if (len > size) len = size; if (len == 0) return 0;
/* =========================================================================== * 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 * OUT assertion: the match length is not greater than s->lookahead.
*/ /* For 80x86 and 680x0, an optimized version will be provided in match.asm or * match.S. The code will be functionally equivalent.
*/ static uInt longest_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 */ registerint len; /* length of current match */ int best_len = s->prev_length; /* best match length so far */ int nice_match = s->nice_match; /* stop if match long enough */
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.
*/
Pos *prev = s->prev;
uInt wmask = s->w_mask;
#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;
} /* Do not look for matches beyond the end of the input. This is necessary * to make deflate deterministic.
*/ if ((uInt)nice_match > s->lookahead) nice_match = s->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.
*/
Assert(scan[2] == match[2], "scan[2]?");
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 */
/* 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++;
Assert(*scan == *match, "match[2]?");
/* 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);
if ((uInt)best_len <= s->lookahead) return best_len; return s->lookahead;
}
#ifdef DEBUG_ZLIB /* =========================================================================== * Check that the match at match_start is indeed a match.
*/ staticvoid check_match(
deflate_state *s,
IPos start,
IPos match, int length
)
{ /* check that the match is indeed a match */ if (memcmp((char *)s->window + match, (char *)s->window + start, length)) {
fprintf(stderr, " start %u, match %u, length %d\n",
start, match, length); do {
fprintf(stderr, "%c%c", s->window[match++], s->window[start++]);
} while (--length != 0);
z_error("invalid match");
} if (z_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).
*/ staticvoid fill_window(
deflate_state *s
)
{ registerunsigned n, m; register Pos *p; unsigned more; /* Amount of free space at the end of the window. */
uInt wsize = s->w_size;
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 = wsize;
} elseif (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.
*/
} elseif (s->strstart >= wsize+MAX_DIST(s)) {
memcpy((char *)s->window, (char *)s->window+wsize,
(unsigned)wsize);
s->match_start -= wsize;
s->strstart -= wsize; /* we now have strstart >= MAX_DIST */
s->block_start -= (long) wsize;
/* Slide the hash table (could be avoided with 32 bit values at the expense of memory usage). We slide even when level == 0 to keep the hash table consistent if we switch back to level > 0 later. (Using level 0 permanently is not an optimal usage of zlib, so we don't care about this pathological case.)
*/
n = s->hash_size;
p = &s->head[n]; do {
m = *--p;
*p = (Pos)(m >= wsize ? m-wsize : NIL);
} while (--n);
n = wsize;
p = &s->prev[n]; do {
m = *--p;
*p = (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.
*/
} while (--n);
more += wsize;
} 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");
/* Initialize the hash value now that we have some input: */ if (s->lookahead >= MIN_MATCH) {
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
} /* If the whole input has less than MIN_MATCH bytes, ins_h is garbage, * but this is not important since only literal bytes will be emitted.
*/
} 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) { \
zlib_tr_flush_block(s, (s->block_start >= 0L ? \
(char *)&s->window[(unsigned)s->block_start] : \
NULL), \
(ulg)((long)s->strstart - s->block_start), \
(eof)); \
s->block_start = s->strstart; \
flush_pending(s->strm); \
Tracev((stderr,"[FLUSH]")); \
}
/* Same but force premature exit if necessary. */ #define FLUSH_BLOCK(s, eof) { \
FLUSH_BLOCK_ONLY(s, eof); \ if (s->strm->avail_out == 0) return (eof) ? finish_started : need_more; \
}
/* =========================================================================== * Copy without compression as much as possible from the input stream, return * the current block state. * This function does not insert new strings in the dictionary since * uncompressible data is probably not useful. This function is used * only for the level=0 compression option. * NOTE: this function should be optimized to avoid extra copying from * window to pending_buf.
*/ static block_state deflate_stored(
deflate_state *s, int flush
)
{ /* Stored blocks are limited to 0xffff bytes, pending_buf is limited * to pending_buf_size, and each stored block has a 5 byte header:
*/
ulg max_block_size = 0xffff;
ulg max_start;
if (s->lookahead == 0) break; /* flush the current block */
}
Assert(s->block_start >= 0L, "block gone");
s->strstart += s->lookahead;
s->lookahead = 0;
/* Emit a stored block if pending_buf will be full: */
max_start = s->block_start + max_block_size; if (s->strstart == 0 || (ulg)s->strstart >= max_start) { /* strstart == 0 is possible when wraparound on 16-bit machine */
s->lookahead = (uInt)(s->strstart - max_start);
s->strstart = (uInt)max_start;
FLUSH_BLOCK(s, 0);
} /* Flush if we may have to slide, otherwise block_start may become * negative and the data will be gone:
*/ if (s->strstart - (uInt)s->block_start >= MAX_DIST(s)) {
FLUSH_BLOCK(s, 0);
}
}
FLUSH_BLOCK(s, flush == Z_FINISH); return flush == Z_FINISH ? finish_done : block_done;
}
/* =========================================================================== * Compress as much as possible from the input stream, return the current * block state. * 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.
*/ static block_state deflate_fast(
deflate_state *s, int flush
)
{
IPos hash_head = NIL; /* head of the hash chain */ int bflush; /* set if current block must be flushed */
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 need_more;
} 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:
*/ if (s->lookahead >= MIN_MATCH) {
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 >= MIN_MATCH) {
check_match(s, s->strstart, s->match_start, 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->lookahead >= MIN_MATCH) {
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.
*/
} 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 /* If lookahead < MIN_MATCH, ins_h is garbage, but it does not * matter since it will be recomputed at next deflate call.
*/
}
} else { /* No match, output a literal byte */
Tracevv((stderr,"%c", s->window[s->strstart]));
bflush = zlib_tr_tally (s, 0, s->window[s->strstart]);
s->lookahead--;
s->strstart++;
} if (bflush) FLUSH_BLOCK(s, 0);
}
FLUSH_BLOCK(s, flush == Z_FINISH); return flush == Z_FINISH ? finish_done : block_done;
}
/* =========================================================================== * 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.
*/ static block_state deflate_slow(
deflate_state *s, int flush
)
{
IPos hash_head = NIL; /* 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 need_more;
} 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:
*/ if (s->lookahead >= MIN_MATCH) {
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 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) {
uInt max_insert = s->strstart + s->lookahead - MIN_MATCH; /* Do not insert strings in hash table beyond this. */
/* Insert in hash table all strings up to the end of the match. * strstart-1 and strstart are already inserted. If there is not * enough lookahead, the last two strings are not inserted in * the hash table.
*/
s->lookahead -= s->prev_length-1;
s->prev_length -= 2; do { if (++s->strstart <= max_insert) {
INSERT_STRING(s, s->strstart, hash_head);
}
} while (--s->prev_length != 0);
s->match_available = 0;
s->match_length = MIN_MATCH-1;
s->strstart++;
if (bflush) FLUSH_BLOCK(s, 0);
} elseif (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 (zlib_tr_tally (s, 0, s->window[s->strstart-1])) {
FLUSH_BLOCK_ONLY(s, 0);
}
s->strstart++;
s->lookahead--; if (s->strm->avail_out == 0) return need_more;
} else { /* There is no previous match to compare with, wait for * the next step to decide.
*/
s->match_available = 1;
s->strstart++;
s->lookahead--;
}
}
Assert (flush != Z_NO_FLUSH, "no flush?"); if (s->match_available) {
Tracevv((stderr,"%c", s->window[s->strstart-1]));
zlib_tr_tally (s, 0, s->window[s->strstart-1]);
s->match_available = 0;
}
FLUSH_BLOCK(s, flush == Z_FINISH); return flush == Z_FINISH ? finish_done : block_done;
}
int zlib_deflate_workspacesize(int windowBits, int memLevel)
{ if (windowBits < 0) /* undocumented feature: suppress zlib header */
windowBits = -windowBits;
/* Since the return value is typically passed to vmalloc() unchecked... */
BUG_ON(memLevel < 1 || memLevel > MAX_MEM_LEVEL || windowBits < 9 ||
windowBits > 15);
Die Informationen auf dieser Webseite wurden
nach bestem Wissen sorgfältig zusammengestellt. Es wird jedoch weder Vollständigkeit, noch Richtigkeit,
noch Qualität der bereit gestellten Informationen zugesichert.
Bemerkung:
Die farbliche Syntaxdarstellung und die Messung sind noch experimentell.
