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deflate.js
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deflate.js
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import * as utils from "../utils/common.js";
import * as trees from "./trees.js";
import adler32 from "./adler32.js";
import crc32 from "./crc32.js";
import msg from "./messages.js";
/* Public constants ==========================================================*/
/* ===========================================================================*/
/* Allowed flush values; see deflate() and inflate() below for details */
export const Z_NO_FLUSH = 0;
export const Z_PARTIAL_FLUSH = 1;
//export const Z_SYNC_FLUSH = 2;
export const Z_FULL_FLUSH = 3;
export const Z_FINISH = 4;
export const Z_BLOCK = 5;
//export const Z_TREES = 6;
/* Return codes for the compression/decompression functions. Negative values
* are errors, positive values are used for special but normal events.
*/
export const Z_OK = 0;
export const Z_STREAM_END = 1;
//export const Z_NEED_DICT = 2;
//export const Z_ERRNO = -1;
export const Z_STREAM_ERROR = -2;
export const Z_DATA_ERROR = -3;
//export const Z_MEM_ERROR = -4;
export const Z_BUF_ERROR = -5;
//export const Z_VERSION_ERROR = -6;
/* compression levels */
//export const Z_NO_COMPRESSION = 0;
//export const Z_BEST_SPEED = 1;
//export const Z_BEST_COMPRESSION = 9;
export const Z_DEFAULT_COMPRESSION = -1;
export const Z_FILTERED = 1;
export const Z_HUFFMAN_ONLY = 2;
export const Z_RLE = 3;
export const Z_FIXED = 4;
export const Z_DEFAULT_STRATEGY = 0;
/* Possible values of the data_type field (though see inflate()) */
//export const Z_BINARY = 0;
//export const Z_TEXT = 1;
//export const Z_ASCII = 1; // = Z_TEXT
export const Z_UNKNOWN = 2;
/* The deflate compression method */
export const Z_DEFLATED = 8;
/*============================================================================*/
var MAX_MEM_LEVEL = 9;
/* Maximum value for memLevel in deflateInit2 */
var MAX_WBITS = 15;
/* 32K LZ77 window */
var DEF_MEM_LEVEL = 8;
var LENGTH_CODES = 29;
/* number of length codes, not counting the special END_BLOCK code */
var LITERALS = 256;
/* number of literal bytes 0..255 */
var L_CODES = LITERALS + 1 + LENGTH_CODES;
/* number of Literal or Length codes, including the END_BLOCK code */
var D_CODES = 30;
/* number of distance codes */
var BL_CODES = 19;
/* number of codes used to transfer the bit lengths */
var HEAP_SIZE = 2 * L_CODES + 1;
/* maximum heap size */
var MAX_BITS = 15;
/* All codes must not exceed MAX_BITS bits */
var MIN_MATCH = 3;
var MAX_MATCH = 258;
var MIN_LOOKAHEAD = (MAX_MATCH + MIN_MATCH + 1);
var PRESET_DICT = 0x20;
var INIT_STATE = 42;
var EXTRA_STATE = 69;
var NAME_STATE = 73;
var COMMENT_STATE = 91;
var HCRC_STATE = 103;
var BUSY_STATE = 113;
var FINISH_STATE = 666;
var BS_NEED_MORE = 1; /* block not completed, need more input or more output */
var BS_BLOCK_DONE = 2; /* block flush performed */
var BS_FINISH_STARTED = 3; /* finish started, need only more output at next deflate */
var BS_FINISH_DONE = 4; /* finish done, accept no more input or output */
var OS_CODE = 0x03; // Unix :) . Don't detect, use this default.
function err(strm, errorCode) {
strm.msg = msg[errorCode];
return errorCode;
}
function rank(f) {
return ((f) << 1) - ((f) > 4 ? 9 : 0);
}
function zero(buf) { var len = buf.length; while (--len >= 0) { buf[len] = 0; } }
/* =========================================================================
* Flush as much pending output as possible. All deflate() output goes
* through this function so some applications may wish to modify it
* to avoid allocating a large strm->output buffer and copying into it.
* (See also read_buf()).
*/
function flush_pending(strm) {
var s = strm.state;
//_tr_flush_bits(s);
var len = s.pending;
if (len > strm.avail_out) {
len = strm.avail_out;
}
if (len === 0) { return; }
utils.arraySet(strm.output, s.pending_buf, s.pending_out, len, strm.next_out);
strm.next_out += len;
s.pending_out += len;
strm.total_out += len;
strm.avail_out -= len;
s.pending -= len;
if (s.pending === 0) {
s.pending_out = 0;
}
}
function flush_block_only(s, last) {
trees._tr_flush_block(s, (s.block_start >= 0 ? s.block_start : -1), s.strstart - s.block_start, last);
s.block_start = s.strstart;
flush_pending(s.strm);
}
function put_byte(s, b) {
s.pending_buf[s.pending++] = b;
}
/* =========================================================================
* 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.
*/
function putShortMSB(s, b) {
// put_byte(s, (Byte)(b >> 8));
// put_byte(s, (Byte)(b & 0xff));
s.pending_buf[s.pending++] = (b >>> 8) & 0xff;
s.pending_buf[s.pending++] = b & 0xff;
}
/* ===========================================================================
* 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->input buffer and copying from it.
* (See also flush_pending()).
*/
function read_buf(strm, buf, start, size) {
var len = strm.avail_in;
if (len > size) { len = size; }
if (len === 0) { return 0; }
strm.avail_in -= len;
// zmemcpy(buf, strm->next_in, len);
utils.arraySet(buf, strm.input, strm.next_in, len, start);
if (strm.state.wrap === 1) {
strm.adler = adler32(strm.adler, buf, len, start);
}
else if (strm.state.wrap === 2) {
strm.adler = crc32(strm.adler, buf, len, start);
}
strm.next_in += len;
strm.total_in += len;
return len;
}
/* ===========================================================================
* 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.
*/
function longest_match(s, cur_match) {
var chain_length = s.max_chain_length; /* max hash chain length */
var scan = s.strstart; /* current string */
var match; /* matched string */
var len; /* length of current match */
var best_len = s.prev_length; /* best match length so far */
var nice_match = s.nice_match; /* stop if match long enough */
var limit = (s.strstart > (s.w_size - MIN_LOOKAHEAD)) ?
s.strstart - (s.w_size - MIN_LOOKAHEAD) : 0/*NIL*/;
var _win = s.window; // shortcut
var wmask = s.w_mask;
var prev = s.prev;
/* Stop when cur_match becomes <= limit. To simplify the code,
* we prevent matches with the string of window index 0.
*/
var strend = s.strstart + MAX_MATCH;
var scan_end1 = _win[scan + best_len - 1];
var scan_end = _win[scan + best_len];
/* 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 (nice_match > s.lookahead) { nice_match = s.lookahead; }
// Assert((ulg)s->strstart <= s->window_size-MIN_LOOKAHEAD, "need lookahead");
do {
// Assert(cur_match < s->strstart, "no future");
match = cur_match;
/* Skip to next match if the match length cannot increase
* or if the match length is less than 2. Note that the checks below
* for insufficient lookahead only occur occasionally for performance
* reasons. Therefore uninitialized memory will be accessed, and
* conditional jumps will be made that depend on those values.
* However the length of the match is limited to the lookahead, so
* the output of deflate is not affected by the uninitialized values.
*/
if (_win[match + best_len] !== scan_end ||
_win[match + best_len - 1] !== scan_end1 ||
_win[match] !== _win[scan] ||
_win[++match] !== _win[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++;
// Assert(*scan == *match, "match[2]?");
/* We check for insufficient lookahead only every 8th comparison;
* the 256th check will be made at strstart+258.
*/
do {
// Do nothing
} while (_win[++scan] === _win[++match] && _win[++scan] === _win[++match] &&
_win[++scan] === _win[++match] && _win[++scan] === _win[++match] &&
_win[++scan] === _win[++match] && _win[++scan] === _win[++match] &&
_win[++scan] === _win[++match] && _win[++scan] === _win[++match] &&
scan < strend);
// Assert(scan <= s->window+(unsigned)(s->window_size-1), "wild scan");
len = MAX_MATCH - (strend - scan);
scan = strend - MAX_MATCH;
if (len > best_len) {
s.match_start = cur_match;
best_len = len;
if (len >= nice_match) {
break;
}
scan_end1 = _win[scan + best_len - 1];
scan_end = _win[scan + best_len];
}
} while ((cur_match = prev[cur_match & wmask]) > limit && --chain_length !== 0);
if (best_len <= s.lookahead) {
return best_len;
}
return s.lookahead;
}
/* ===========================================================================
* 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).
*/
function fill_window(s) {
var _w_size = s.w_size;
var p, n, m, more, str;
//Assert(s->lookahead < MIN_LOOKAHEAD, "already enough lookahead");
do {
more = s.window_size - s.lookahead - s.strstart;
// JS ints have 32 bit, block below not needed
/* Deal with !@#$% 64K limit: */
//if (sizeof(int) <= 2) {
// if (more == 0 && s->strstart == 0 && s->lookahead == 0) {
// more = wsize;
//
// } else if (more == (unsigned)(-1)) {
// /* Very unlikely, but possible on 16 bit machine if
// * strstart == 0 && lookahead == 1 (input done a 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.
*/
if (s.strstart >= _w_size + (_w_size - MIN_LOOKAHEAD)) {
utils.arraySet(s.window, s.window, _w_size, _w_size, 0);
s.match_start -= _w_size;
s.strstart -= _w_size;
/* we now have strstart >= MAX_DIST */
s.block_start -= _w_size;
/* 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 = n;
do {
m = s.head[--p];
s.head[p] = (m >= _w_size ? m - _w_size : 0);
} while (--n);
n = _w_size;
p = n;
do {
m = s.prev[--p];
s.prev[p] = (m >= _w_size ? m - _w_size : 0);
/* If n is not on any hash chain, prev[n] is garbage but
* its value will never be used.
*/
} while (--n);
more += _w_size;
}
if (s.strm.avail_in === 0) {
break;
}
/* 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, s.window, s.strstart + s.lookahead, more);
s.lookahead += n;
/* Initialize the hash value now that we have some input: */
if (s.lookahead + s.insert >= MIN_MATCH) {
str = s.strstart - s.insert;
s.ins_h = s.window[str];
/* UPDATE_HASH(s, s->ins_h, s->window[str + 1]); */
s.ins_h = ((s.ins_h << s.hash_shift) ^ s.window[str + 1]) & s.hash_mask;
//#if MIN_MATCH != 3
// Call update_hash() MIN_MATCH-3 more times
//#endif
while (s.insert) {
/* UPDATE_HASH(s, s->ins_h, s->window[str + MIN_MATCH-1]); */
s.ins_h = ((s.ins_h << s.hash_shift) ^ s.window[str + MIN_MATCH - 1]) & s.hash_mask;
s.prev[str & s.w_mask] = s.head[s.ins_h];
s.head[s.ins_h] = str;
str++;
s.insert--;
if (s.lookahead + s.insert < MIN_MATCH) {
break;
}
}
}
/* 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);
/* If the WIN_INIT bytes after the end of the current data have never been
* written, then zero those bytes in order to avoid memory check reports of
* the use of uninitialized (or uninitialised as Julian writes) bytes by
* the longest match routines. Update the high water mark for the next
* time through here. WIN_INIT is set to MAX_MATCH since the longest match
* routines allow scanning to strstart + MAX_MATCH, ignoring lookahead.
*/
// if (s.high_water < s.window_size) {
// var curr = s.strstart + s.lookahead;
// var init = 0;
//
// if (s.high_water < curr) {
// /* Previous high water mark below current data -- zero WIN_INIT
// * bytes or up to end of window, whichever is less.
// */
// init = s.window_size - curr;
// if (init > WIN_INIT)
// init = WIN_INIT;
// zmemzero(s->window + curr, (unsigned)init);
// s->high_water = curr + init;
// }
// else if (s->high_water < (ulg)curr + WIN_INIT) {
// /* High water mark at or above current data, but below current data
// * plus WIN_INIT -- zero out to current data plus WIN_INIT, or up
// * to end of window, whichever is less.
// */
// init = (ulg)curr + WIN_INIT - s->high_water;
// if (init > s->window_size - s->high_water)
// init = s->window_size - s->high_water;
// zmemzero(s->window + s->high_water, (unsigned)init);
// s->high_water += init;
// }
// }
//
// Assert((ulg)s->strstart <= s->window_size - MIN_LOOKAHEAD,
// "not enough room for search");
}
/* ===========================================================================
* 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.
*/
function deflate_stored(s, 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:
*/
var max_block_size = 0xffff;
if (max_block_size > s.pending_buf_size - 5) {
max_block_size = s.pending_buf_size - 5;
}
/* Copy as much as possible from input to output: */
for (;;) {
/* Fill the window as much as possible: */
if (s.lookahead <= 1) {
//Assert(s->strstart < s->w_size+MAX_DIST(s) ||
// s->block_start >= (long)s->w_size, "slide too late");
// if (!(s.strstart < s.w_size + (s.w_size - MIN_LOOKAHEAD) ||
// s.block_start >= s.w_size)) {
// throw new Error("slide too late");
// }
fill_window(s);
if (s.lookahead === 0 && flush === Z_NO_FLUSH) {
return BS_NEED_MORE;
}
if (s.lookahead === 0) {
break;
}
/* flush the current block */
}
//Assert(s->block_start >= 0L, "block gone");
// if (s.block_start < 0) throw new Error("block gone");
s.strstart += s.lookahead;
s.lookahead = 0;
/* Emit a stored block if pending_buf will be full: */
var max_start = s.block_start + max_block_size;
if (s.strstart === 0 || s.strstart >= max_start) {
/* strstart == 0 is possible when wraparound on 16-bit machine */
s.lookahead = s.strstart - max_start;
s.strstart = max_start;
/*** FLUSH_BLOCK(s, 0); ***/
flush_block_only(s, false);
if (s.strm.avail_out === 0) {
return BS_NEED_MORE;
}
/***/
}
/* Flush if we may have to slide, otherwise block_start may become
* negative and the data will be gone:
*/
if (s.strstart - s.block_start >= (s.w_size - MIN_LOOKAHEAD)) {
/*** FLUSH_BLOCK(s, 0); ***/
flush_block_only(s, false);
if (s.strm.avail_out === 0) {
return BS_NEED_MORE;
}
/***/
}
}
s.insert = 0;
if (flush === Z_FINISH) {
/*** FLUSH_BLOCK(s, 1); ***/
flush_block_only(s, true);
if (s.strm.avail_out === 0) {
return BS_FINISH_STARTED;
}
/***/
return BS_FINISH_DONE;
}
if (s.strstart > s.block_start) {
/*** FLUSH_BLOCK(s, 0); ***/
flush_block_only(s, false);
if (s.strm.avail_out === 0) {
return BS_NEED_MORE;
}
/***/
}
return BS_NEED_MORE;
}
/* ===========================================================================
* 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.
*/
function deflate_fast(s, flush) {
var hash_head; /* head of the hash chain */
var 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 BS_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:
*/
hash_head = 0/*NIL*/;
if (s.lookahead >= MIN_MATCH) {
/*** INSERT_STRING(s, s.strstart, hash_head); ***/
s.ins_h = ((s.ins_h << s.hash_shift) ^ s.window[s.strstart + MIN_MATCH - 1]) & s.hash_mask;
hash_head = s.prev[s.strstart & s.w_mask] = s.head[s.ins_h];
s.head[s.ins_h] = s.strstart;
/***/
}
/* Find the longest match, discarding those <= prev_length.
* At this point we have always match_length < MIN_MATCH
*/
if (hash_head !== 0/*NIL*/ && ((s.strstart - hash_head) <= (s.w_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).
*/
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); // for debug only
/*** _tr_tally_dist(s, s.strstart - s.match_start,
s.match_length - MIN_MATCH, bflush); ***/
bflush = trees._tr_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_lazy_match/*max_insert_length*/ && s.lookahead >= MIN_MATCH) {
s.match_length--; /* string at strstart already in table */
do {
s.strstart++;
/*** INSERT_STRING(s, s.strstart, hash_head); ***/
s.ins_h = ((s.ins_h << s.hash_shift) ^ s.window[s.strstart + MIN_MATCH - 1]) & s.hash_mask;
hash_head = s.prev[s.strstart & s.w_mask] = s.head[s.ins_h];
s.head[s.ins_h] = s.strstart;
/***/
/* 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]); */
s.ins_h = ((s.ins_h << s.hash_shift) ^ s.window[s.strstart + 1]) & s.hash_mask;
//#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]));
/*** _tr_tally_lit(s, s.window[s.strstart], bflush); ***/
bflush = trees._tr_tally(s, 0, s.window[s.strstart]);
s.lookahead--;
s.strstart++;
}
if (bflush) {
/*** FLUSH_BLOCK(s, 0); ***/
flush_block_only(s, false);
if (s.strm.avail_out === 0) {
return BS_NEED_MORE;
}
/***/
}
}
s.insert = ((s.strstart < (MIN_MATCH - 1)) ? s.strstart : MIN_MATCH - 1);
if (flush === Z_FINISH) {
/*** FLUSH_BLOCK(s, 1); ***/
flush_block_only(s, true);
if (s.strm.avail_out === 0) {
return BS_FINISH_STARTED;
}
/***/
return BS_FINISH_DONE;
}
if (s.last_lit) {
/*** FLUSH_BLOCK(s, 0); ***/
flush_block_only(s, false);
if (s.strm.avail_out === 0) {
return BS_NEED_MORE;
}
/***/
}
return BS_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.
*/
function deflate_slow(s, flush) {
var hash_head; /* head of hash chain */
var bflush; /* set if current block must be flushed */
var max_insert;
/* 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 BS_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:
*/
hash_head = 0/*NIL*/;
if (s.lookahead >= MIN_MATCH) {
/*** INSERT_STRING(s, s.strstart, hash_head); ***/
s.ins_h = ((s.ins_h << s.hash_shift) ^ s.window[s.strstart + MIN_MATCH - 1]) & s.hash_mask;
hash_head = s.prev[s.strstart & s.w_mask] = s.head[s.ins_h];
s.head[s.ins_h] = s.strstart;
/***/
}
/* 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 !== 0/*NIL*/ && s.prev_length < s.max_lazy_match &&
s.strstart - hash_head <= (s.w_size - MIN_LOOKAHEAD)/*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).
*/
s.match_length = longest_match(s, hash_head);
/* longest_match() sets match_start */
if (s.match_length <= 5 &&
(s.strategy === Z_FILTERED || (s.match_length === MIN_MATCH && s.strstart - s.match_start > 4096/*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) {
max_insert = s.strstart + s.lookahead - MIN_MATCH;
/* Do not insert strings in hash table beyond this. */
//check_match(s, s.strstart-1, s.prev_match, s.prev_length);
/***_tr_tally_dist(s, s.strstart - 1 - s.prev_match,
s.prev_length - MIN_MATCH, bflush);***/
bflush = trees._tr_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. 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); ***/
s.ins_h = ((s.ins_h << s.hash_shift) ^ s.window[s.strstart + MIN_MATCH - 1]) & s.hash_mask;
hash_head = s.prev[s.strstart & s.w_mask] = s.head[s.ins_h];
s.head[s.ins_h] = s.strstart;
/***/
}
} while (--s.prev_length !== 0);
s.match_available = 0;
s.match_length = MIN_MATCH - 1;
s.strstart++;
if (bflush) {
/*** FLUSH_BLOCK(s, 0); ***/
flush_block_only(s, false);
if (s.strm.avail_out === 0) {
return BS_NEED_MORE;
}
/***/
}
} 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]));
/*** _tr_tally_lit(s, s.window[s.strstart-1], bflush); ***/
bflush = trees._tr_tally(s, 0, s.window[s.strstart - 1]);
if (bflush) {
/*** FLUSH_BLOCK_ONLY(s, 0) ***/
flush_block_only(s, false);
/***/
}
s.strstart++;
s.lookahead--;
if (s.strm.avail_out === 0) {
return BS_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]));
/*** _tr_tally_lit(s, s.window[s.strstart-1], bflush); ***/
bflush = trees._tr_tally(s, 0, s.window[s.strstart - 1]);
s.match_available = 0;
}
s.insert = s.strstart < MIN_MATCH - 1 ? s.strstart : MIN_MATCH - 1;
if (flush === Z_FINISH) {
/*** FLUSH_BLOCK(s, 1); ***/
flush_block_only(s, true);
if (s.strm.avail_out === 0) {
return BS_FINISH_STARTED;
}
/***/
return BS_FINISH_DONE;
}
if (s.last_lit) {
/*** FLUSH_BLOCK(s, 0); ***/
flush_block_only(s, false);
if (s.strm.avail_out === 0) {
return BS_NEED_MORE;
}
/***/
}
return BS_BLOCK_DONE;
}
/* ===========================================================================
* For Z_RLE, simply look for runs of bytes, generate matches only of distance
* one. Do not maintain a hash table. (It will be regenerated if this run of
* deflate switches away from Z_RLE.)
*/
function deflate_rle(s, flush) {
var bflush; /* set if current block must be flushed */
var prev; /* byte at distance one to match */
var scan, strend; /* scan goes up to strend for length of run */
var _win = s.window;
for (;;) {
/* Make sure that we always have enough lookahead, except
* at the end of the input file. We need MAX_MATCH bytes
* for the longest run, plus one for the unrolled loop.
*/
if (s.lookahead <= MAX_MATCH) {
fill_window(s);
if (s.lookahead <= MAX_MATCH && flush === Z_NO_FLUSH) {
return BS_NEED_MORE;
}
if (s.lookahead === 0) { break; } /* flush the current block */
}
/* See how many times the previous byte repeats */
s.match_length = 0;
if (s.lookahead >= MIN_MATCH && s.strstart > 0) {
scan = s.strstart - 1;
prev = _win[scan];
if (prev === _win[++scan] && prev === _win[++scan] && prev === _win[++scan]) {
strend = s.strstart + MAX_MATCH;
do {
// Do nothing
} while (prev === _win[++scan] && prev === _win[++scan] &&
prev === _win[++scan] && prev === _win[++scan] &&
prev === _win[++scan] && prev === _win[++scan] &&
prev === _win[++scan] && prev === _win[++scan] &&
scan < strend);
s.match_length = MAX_MATCH - (strend - scan);
if (s.match_length > s.lookahead) {
s.match_length = s.lookahead;
}
}
//Assert(scan <= s->window+(uInt)(s->window_size-1), "wild scan");
}
/* Emit match if have run of MIN_MATCH or longer, else emit literal */
if (s.match_length >= MIN_MATCH) {
//check_match(s, s.strstart, s.strstart - 1, s.match_length);
/*** _tr_tally_dist(s, 1, s.match_length - MIN_MATCH, bflush); ***/
bflush = trees._tr_tally(s, 1, s.match_length - MIN_MATCH);
s.lookahead -= s.match_length;
s.strstart += s.match_length;
s.match_length = 0;
} else {
/* No match, output a literal byte */
//Tracevv((stderr,"%c", s->window[s->strstart]));
/*** _tr_tally_lit(s, s.window[s.strstart], bflush); ***/
bflush = trees._tr_tally(s, 0, s.window[s.strstart]);
s.lookahead--;
s.strstart++;
}
if (bflush) {
/*** FLUSH_BLOCK(s, 0); ***/
flush_block_only(s, false);
if (s.strm.avail_out === 0) {
return BS_NEED_MORE;
}
/***/
}
}
s.insert = 0;
if (flush === Z_FINISH) {
/*** FLUSH_BLOCK(s, 1); ***/
flush_block_only(s, true);
if (s.strm.avail_out === 0) {
return BS_FINISH_STARTED;
}
/***/
return BS_FINISH_DONE;
}
if (s.last_lit) {
/*** FLUSH_BLOCK(s, 0); ***/
flush_block_only(s, false);
if (s.strm.avail_out === 0) {
return BS_NEED_MORE;
}
/***/
}
return BS_BLOCK_DONE;
}
/* ===========================================================================
* For Z_HUFFMAN_ONLY, do not look for matches. Do not maintain a hash table.
* (It will be regenerated if this run of deflate switches away from Huffman.)
*/
function deflate_huff(s, flush) {
var bflush; /* set if current block must be flushed */
for (;;) {
/* Make sure that we have a literal to write. */
if (s.lookahead === 0) {
fill_window(s);
if (s.lookahead === 0) {
if (flush === Z_NO_FLUSH) {
return BS_NEED_MORE;
}
break; /* flush the current block */
}
}
/* Output a literal byte */
s.match_length = 0;
//Tracevv((stderr,"%c", s->window[s->strstart]));
/*** _tr_tally_lit(s, s.window[s.strstart], bflush); ***/
bflush = trees._tr_tally(s, 0, s.window[s.strstart]);
s.lookahead--;
s.strstart++;
if (bflush) {
/*** FLUSH_BLOCK(s, 0); ***/
flush_block_only(s, false);
if (s.strm.avail_out === 0) {
return BS_NEED_MORE;
}
/***/
}
}
s.insert = 0;
if (flush === Z_FINISH) {
/*** FLUSH_BLOCK(s, 1); ***/
flush_block_only(s, true);
if (s.strm.avail_out === 0) {
return BS_FINISH_STARTED;
}
/***/