偶然得到份js,试着做成php未果,敢请高手帮忙

sigoo3 2009-08-02 07:37:46
js太长了,分成好几段发上来

/* constant parameters */
var zip_WSIZE = 32768; // Sliding Window size
var zip_STORED_BLOCK = 0;
var zip_STATIC_TREES = 1;
var zip_DYN_TREES = 2;

/* for deflate */
var zip_DEFAULT_LEVEL = 6;
var zip_FULL_SEARCH = true;
var zip_INBUFSIZ = 32768; // Input buffer size
var zip_INBUF_EXTRA = 64; // Extra buffer
var zip_OUTBUFSIZ = 1024 * 8;
var zip_window_size = 2 * zip_WSIZE;
var zip_MIN_MATCH = 3;
var zip_MAX_MATCH = 258;
var zip_BITS = 16;
// for SMALL_MEM
var zip_LIT_BUFSIZE = 0x2000;
var zip_HASH_BITS = 13;
// for MEDIUM_MEM
// var zip_LIT_BUFSIZE = 0x4000;
// var zip_HASH_BITS = 14;
// for BIG_MEM
// var zip_LIT_BUFSIZE = 0x8000;
// var zip_HASH_BITS = 15;
if(zip_LIT_BUFSIZE > zip_INBUFSIZ)
alert("error: zip_INBUFSIZ is too small");
if((zip_WSIZE<<1) > (1<<zip_BITS))
alert("error: zip_WSIZE is too large");
if(zip_HASH_BITS > zip_BITS-1)
alert("error: zip_HASH_BITS is too large");
if(zip_HASH_BITS < 8 || zip_MAX_MATCH != 258)
alert("error: Code too clever");
var zip_DIST_BUFSIZE = zip_LIT_BUFSIZE;
var zip_HASH_SIZE = 1 << zip_HASH_BITS;
var zip_HASH_MASK = zip_HASH_SIZE - 1;
var zip_WMASK = zip_WSIZE - 1;
var zip_NIL = 0; // Tail of hash chains
var zip_TOO_FAR = 4096;
var zip_MIN_LOOKAHEAD = zip_MAX_MATCH + zip_MIN_MATCH + 1;
var zip_MAX_DIST = zip_WSIZE - zip_MIN_LOOKAHEAD;
var zip_SMALLEST = 1;
var zip_MAX_BITS = 15;
var zip_MAX_BL_BITS = 7;
var zip_LENGTH_CODES = 29;
var zip_LITERALS =256;
var zip_END_BLOCK = 256;
var zip_L_CODES = zip_LITERALS + 1 + zip_LENGTH_CODES;
var zip_D_CODES = 30;
var zip_BL_CODES = 19;
var zip_REP_3_6 = 16;
var zip_REPZ_3_10 = 17;
var zip_REPZ_11_138 = 18;
var zip_HEAP_SIZE = 2 * zip_L_CODES + 1;
var zip_H_SHIFT = parseInt((zip_HASH_BITS + zip_MIN_MATCH - 1) /
zip_MIN_MATCH);

/* variables */
var zip_free_queue;
var zip_qhead, zip_qtail;
var zip_initflag;
var zip_outbuf = null;
var zip_outcnt, zip_outoff;
var zip_complete;
var zip_window;
var zip_d_buf;
var zip_l_buf;
var zip_prev;
var zip_bi_buf;
var zip_bi_valid;
var zip_block_start;
var zip_ins_h;
var zip_hash_head;
var zip_prev_match;
var zip_match_available;
var zip_match_length;
var zip_prev_length;
var zip_strstart;
var zip_match_start;
var zip_eofile;
var zip_lookahead;
var zip_max_chain_length;
var zip_max_lazy_match;
var zip_compr_level;
var zip_good_match;
var zip_nice_match;
var zip_dyn_ltree;
var zip_dyn_dtree;
var zip_static_ltree;
var zip_static_dtree;
var zip_bl_tree;
var zip_l_desc;
var zip_d_desc;
var zip_bl_desc;
var zip_bl_count;
var zip_heap;
var zip_heap_len;
var zip_heap_max;
var zip_depth;
var zip_length_code;
var zip_dist_code;
var zip_base_length;
var zip_base_dist;
var zip_flag_buf;
var zip_last_lit;
var zip_last_dist;
var zip_last_flags;
var zip_flags;
var zip_flag_bit;
var zip_opt_len;
var zip_static_len;
var zip_deflate_data;
var zip_deflate_pos;

/* constant tables */
var zip_extra_lbits = new Array(
0,0,0,0,0,0,0,0,1,1,1,1,2,2,2,2,3,3,3,3,4,4,4,4,5,5,5,5,0);
var zip_extra_dbits = new Array(
0,0,0,0,1,1,2,2,3,3,4,4,5,5,6,6,7,7,8,8,9,9,10,10,11,11,12,12,13,13);
var zip_extra_blbits = new Array(
0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,2,3,7);
var zip_bl_order = new Array(
16,17,18,0,8,7,9,6,10,5,11,4,12,3,13,2,14,1,15);
var zip_configuration_table = new Array(
new zip_DeflateConfiguration(0, 0, 0, 0),
new zip_DeflateConfiguration(4, 4, 8, 4),
new zip_DeflateConfiguration(4, 5, 16, 8),
new zip_DeflateConfiguration(4, 6, 32, 32),
new zip_DeflateConfiguration(4, 4, 16, 16),
new zip_DeflateConfiguration(8, 16, 32, 32),
new zip_DeflateConfiguration(8, 16, 128, 128),
new zip_DeflateConfiguration(8, 32, 128, 256),
new zip_DeflateConfiguration(32, 128, 258, 1024),
new zip_DeflateConfiguration(32, 258, 258, 4096));

/* objects (deflate) */


function zip_DeflateCT() {
this.fc = 0; // frequency count or bit string
this.dl = 0; // father node in Huffman tree or length of bit string
}

function zip_DeflateTreeDesc() {
this.dyn_tree = null; // the dynamic tree
this.static_tree = null; // corresponding static tree or NULL
this.extra_bits = null; // extra bits for each code or NULL
this.extra_base = 0; // base index for extra_bits
this.elems = 0; // max number of elements in the tree
this.max_length = 0; // max bit length for the codes
this.max_code = 0; // largest code with non zero frequency
}

/* 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.
*/
function zip_DeflateConfiguration(a, b, c, d) {
this.good_length = a; // reduce lazy search above this match length
this.max_lazy = b; // do not perform lazy search above this match length
this.nice_length = c; // quit search above this match length
this.max_chain = d;
}

function zip_DeflateBuffer() {
this.next = null;
this.len = 0;
this.ptr = new Array(zip_OUTBUFSIZ);
this.off = 0;
}

/* routines (deflate) */

function zip_deflate_start(level) {
var i;

if(!level)
level = zip_DEFAULT_LEVEL;
else if(level < 1)
level = 1;
else if(level > 9)
level = 9;

zip_compr_level = level;
zip_initflag = false;
zip_eofile = false;
if(zip_outbuf != null)
return;

zip_free_queue = zip_qhead = zip_qtail = null;
zip_outbuf = new Array(zip_OUTBUFSIZ);
zip_window = new Array(zip_window_size);
zip_d_buf = new Array(zip_DIST_BUFSIZE);
zip_l_buf = new Array(zip_INBUFSIZ + zip_INBUF_EXTRA);
zip_prev = new Array(1 << zip_BITS);
zip_dyn_ltree = new Array(zip_HEAP_SIZE);
for(i = 0; i < zip_HEAP_SIZE; i++)
zip_dyn_ltree[i] = new zip_DeflateCT();
zip_dyn_dtree = new Array(2*zip_D_CODES+1);
for(i = 0; i < 2*zip_D_CODES+1; i++)
zip_dyn_dtree[i] = new zip_DeflateCT();
zip_static_ltree = new Array(zip_L_CODES+2);
for(i = 0; i < zip_L_CODES+2; i++)
zip_static_ltree[i] = new zip_DeflateCT();
zip_static_dtree = new Array(zip_D_CODES);
for(i = 0; i < zip_D_CODES; i++)
zip_static_dtree[i] = new zip_DeflateCT();
zip_bl_tree = new Array(2*zip_BL_CODES+1);
for(i = 0; i < 2*zip_BL_CODES+1; i++)
zip_bl_tree[i] = new zip_DeflateCT();
zip_l_desc = new zip_DeflateTreeDesc();
zip_d_desc = new zip_DeflateTreeDesc();
zip_bl_desc = new zip_DeflateTreeDesc();
zip_bl_count = new Array(zip_MAX_BITS+1);
zip_heap = new Array(2*zip_L_CODES+1);
zip_depth = new Array(2*zip_L_CODES+1);
zip_length_code = new Array(zip_MAX_MATCH-zip_MIN_MATCH+1);
zip_dist_code = new Array(512);
zip_base_length = new Array(zip_LENGTH_CODES);
zip_base_dist = new Array(zip_D_CODES);
zip_flag_buf = new Array(parseInt(zip_LIT_BUFSIZE / 8));
}

function zip_deflate_end() {
zip_free_queue = zip_qhead = zip_qtail = null;
zip_outbuf = null;
zip_window = null;
zip_d_buf = null;
zip_l_buf = null;
zip_prev = null;
zip_dyn_ltree = null;
zip_dyn_dtree = null;
zip_static_ltree = null;
zip_static_dtree = null;
zip_bl_tree = null;
zip_l_desc = null;
zip_d_desc = null;
zip_bl_desc = null;
zip_bl_count = null;
zip_heap = null;
zip_depth = null;
zip_length_code = null;
zip_dist_code = null;
zip_base_length = null;
zip_base_dist = null;
zip_flag_buf = null;
}

function zip_reuse_queue(p) {
p.next = zip_free_queue;
zip_free_queue = p;
}

...全文
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sigoo3 2009-08-03
但是PHP自带的inflate压缩js没法解压出来
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jiewenxu 2009-08-03
哦。我看出来了。楼主的是拿的一个JS的inflate算法,是ZIP压缩的一种。想必楼主是想用来加密解密一些敏感数据,顺便可以压缩。呵呵

想说的是,PHP已经自带了inflate的加密和解密算法了,就是gzinflate()和gzdeflate()。楼主可以自己试试。呵呵
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ruanchao 2009-08-02
楼主,你很有才啊

这么多代码,说说你要实现的效果吧。
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sigoo3 2009-08-02

function zip_deflate_better() {
/* Process the input block. */
while(zip_lookahead != 0 && zip_qhead == null) {
/* Insert the string window[strstart .. strstart+2] in the
* dictionary, and set hash_head to the head of the hash chain:
*/
zip_INSERT_STRING();

/* Find the longest match, discarding those <= prev_length.
*/
zip_prev_length = zip_match_length;
zip_prev_match = zip_match_start;
zip_match_length = zip_MIN_MATCH - 1;

if(zip_hash_head != zip_NIL &&
zip_prev_length < zip_max_lazy_match &&
zip_strstart - zip_hash_head <= zip_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).
*/
zip_match_length = zip_longest_match(zip_hash_head);
/* longest_match() sets match_start */
if(zip_match_length > zip_lookahead)
zip_match_length = zip_lookahead;

/* Ignore a length 3 match if it is too distant: */
if(zip_match_length == zip_MIN_MATCH &&
zip_strstart - zip_match_start > zip_TOO_FAR) {
/* If prev_match is also MIN_MATCH, match_start is garbage
* but we will ignore the current match anyway.
*/
zip_match_length--;
}
}
/* If there was a match at the previous step and the current
* match is not better, output the previous match:
*/
if(zip_prev_length >= zip_MIN_MATCH &&
zip_match_length <= zip_prev_length) {
var flush; // set if current block must be flushed

// check_match(strstart - 1, prev_match, prev_length);
flush = zip_ct_tally(zip_strstart - 1 - zip_prev_match,
zip_prev_length - zip_MIN_MATCH);

/* Insert in hash table all strings up to the end of the match.
* strstart-1 and strstart are already inserted.
*/
zip_lookahead -= zip_prev_length - 1;
zip_prev_length -= 2;
do {
zip_strstart++;
zip_INSERT_STRING();
/* 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(--zip_prev_length != 0);
zip_match_available = 0;
zip_match_length = zip_MIN_MATCH - 1;
zip_strstart++;
if(flush) {
zip_flush_block(0);
zip_block_start = zip_strstart;
}
} else if(zip_match_available != 0) {
/* 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.
*/
if(zip_ct_tally(0, zip_window[zip_strstart - 1] & 0xff)) {
zip_flush_block(0);
zip_block_start = zip_strstart;
}
zip_strstart++;
zip_lookahead--;
} else {
/* There is no previous match to compare with, wait for
* the next step to decide.
*/
zip_match_available = 1;
zip_strstart++;
zip_lookahead--;
}

/* 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(zip_lookahead < zip_MIN_LOOKAHEAD && !zip_eofile)
zip_fill_window();
}
}

function zip_init_deflate() {
if(zip_eofile)
return;
zip_bi_buf = 0;
zip_bi_valid = 0;
zip_ct_init();
zip_lm_init();

zip_qhead = null;
zip_outcnt = 0;
zip_outoff = 0;

if(zip_compr_level <= 3)
{
zip_prev_length = zip_MIN_MATCH - 1;
zip_match_length = 0;
}
else
{
zip_match_length = zip_MIN_MATCH - 1;
zip_match_available = 0;
}

zip_complete = false;
}
回复
sigoo3 2009-08-02



/* ==========================================================================
* 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).
*/
function zip_fill_window() {
var n, m;

// Amount of free space at the end of the window.
var more = zip_window_size - zip_lookahead - zip_strstart;

/* 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 == -1) {
/* Very unlikely, but possible on 16 bit machine if strstart == 0
* and lookahead == 1 (input done one byte at time)
*/
more--;
} else if(zip_strstart >= zip_WSIZE + zip_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");

// System.arraycopy(window, WSIZE, window, 0, WSIZE);
for(n = 0; n < zip_WSIZE; n++)
zip_window[n] = zip_window[n + zip_WSIZE];

zip_match_start -= zip_WSIZE;
zip_strstart -= zip_WSIZE; /* we now have strstart >= MAX_DIST: */
zip_block_start -= zip_WSIZE;

for(n = 0; n < zip_HASH_SIZE; n++) {
m = zip_head1(n);
zip_head2(n, m >= zip_WSIZE ? m - zip_WSIZE : zip_NIL);
}
for(n = 0; n < zip_WSIZE; n++) {
/* If n is not on any hash chain, prev[n] is garbage but
* its value will never be used.
*/
m = zip_prev[n];
zip_prev[n] = (m >= zip_WSIZE ? m - zip_WSIZE : zip_NIL);
}
more += zip_WSIZE;
}
// At this point, more >= 2
if(!zip_eofile) {
n = zip_read_buff(zip_window, zip_strstart + zip_lookahead, more);
if(n <= 0)
zip_eofile = true;
else
zip_lookahead += n;
}
}

/* ==========================================================================
* 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.
*/
function zip_deflate_fast() {
while(zip_lookahead != 0 && zip_qhead == null) {
var flush; // set if current block must be flushed

/* Insert the string window[strstart .. strstart+2] in the
* dictionary, and set hash_head to the head of the hash chain:
*/
zip_INSERT_STRING();

/* Find the longest match, discarding those <= prev_length.
* At this point we have always match_length < MIN_MATCH
*/
if(zip_hash_head != zip_NIL &&
zip_strstart - zip_hash_head <= zip_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).
*/
zip_match_length = zip_longest_match(zip_hash_head);
/* longest_match() sets match_start */
if(zip_match_length > zip_lookahead)
zip_match_length = zip_lookahead;
}
if(zip_match_length >= zip_MIN_MATCH) {
// check_match(strstart, match_start, match_length);

flush = zip_ct_tally(zip_strstart - zip_match_start,
zip_match_length - zip_MIN_MATCH);
zip_lookahead -= zip_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(zip_match_length <= zip_max_lazy_match) {
zip_match_length--; // string at strstart already in hash table
do {
zip_strstart++;
zip_INSERT_STRING();
/* 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(--zip_match_length != 0);
zip_strstart++;
} else {
zip_strstart += zip_match_length;
zip_match_length = 0;
zip_ins_h = zip_window[zip_strstart] & 0xff;
// UPDATE_HASH(ins_h, window[strstart + 1]);
zip_ins_h = ((zip_ins_h<<zip_H_SHIFT) ^ (zip_window[zip_strstart + 1] & 0xff)) & zip_HASH_MASK;

//#if MIN_MATCH != 3
// Call UPDATE_HASH() MIN_MATCH-3 more times
//#endif

}
} else {
/* No match, output a literal byte */
flush = zip_ct_tally(0, zip_window[zip_strstart] & 0xff);
zip_lookahead--;
zip_strstart++;
}
if(flush) {
zip_flush_block(0);
zip_block_start = zip_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(zip_lookahead < zip_MIN_LOOKAHEAD && !zip_eofile)
zip_fill_window();
}
}

回复
sigoo3 2009-08-02


function zip_new_queue() {
var p;

if(zip_free_queue != null)
{
p = zip_free_queue;
zip_free_queue = zip_free_queue.next;
}
else
p = new zip_DeflateBuffer();
p.next = null;
p.len = p.off = 0;

return p;
}

function zip_head1(i) {
return zip_prev[zip_WSIZE + i];
}

function zip_head2(i, val) {
return zip_prev[zip_WSIZE + i] = val;
}

/* put_byte is used for the compressed output, put_ubyte for the
* uncompressed output. However unlzw() uses window for its
* suffix table instead of its output buffer, so it does not use put_ubyte
* (to be cleaned up).
*/
function zip_put_byte(c) {
zip_outbuf[zip_outoff + zip_outcnt++] = c;
if(zip_outoff + zip_outcnt == zip_OUTBUFSIZ)
zip_qoutbuf();
}

/* Output a 16 bit value, lsb first */
function zip_put_short(w) {
w &= 0xffff;
if(zip_outoff + zip_outcnt < zip_OUTBUFSIZ - 2) {
zip_outbuf[zip_outoff + zip_outcnt++] = (w & 0xff);
zip_outbuf[zip_outoff + zip_outcnt++] = (w >>> 8);
} else {
zip_put_byte(w & 0xff);
zip_put_byte(w >>> 8);
}
}

/* ==========================================================================
* 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).
*/
function zip_INSERT_STRING() {
zip_ins_h = ((zip_ins_h << zip_H_SHIFT)
^ (zip_window[zip_strstart + zip_MIN_MATCH - 1] & 0xff))
& zip_HASH_MASK;
zip_hash_head = zip_head1(zip_ins_h);
zip_prev[zip_strstart & zip_WMASK] = zip_hash_head;
zip_head2(zip_ins_h, zip_strstart);
}

/* Send a code of the given tree. c and tree must not have side effects */
function zip_SEND_CODE(c, tree) {
zip_send_bits(tree[c].fc, tree[c].dl);
}

/* Mapping from a distance to a distance code. dist is the distance - 1 and
* must not have side effects. dist_code[256] and dist_code[257] are never
* used.
*/
function zip_D_CODE(dist) {
return (dist < 256 ? zip_dist_code[dist]
: zip_dist_code[256 + (dist>>7)]) & 0xff;
}

/* ==========================================================================
* Compares to subtrees, using the tree depth as tie breaker when
* the subtrees have equal frequency. This minimizes the worst case length.
*/
function zip_SMALLER(tree, n, m) {
return tree[n].fc < tree[m].fc ||
(tree[n].fc == tree[m].fc && zip_depth[n] <= zip_depth[m]);
}

/* ==========================================================================
* read string data
*/
function zip_read_buff(buff, offset, n) {
var i;
for(i = 0; i < n && zip_deflate_pos < zip_deflate_data.length; i++)
buff[offset + i] =
zip_deflate_data.charCodeAt(zip_deflate_pos++) & 0xff;
return i;
}

/* ==========================================================================
* Initialize the "longest match" routines for a new file
*/
function zip_lm_init() {
var j;

/* Initialize the hash table. */
for(j = 0; j < zip_HASH_SIZE; j++)
// zip_head2(j, zip_NIL);
zip_prev[zip_WSIZE + j] = 0;
/* prev will be initialized on the fly */

/* Set the default configuration parameters:
*/
zip_max_lazy_match = zip_configuration_table[zip_compr_level].max_lazy;
zip_good_match = zip_configuration_table[zip_compr_level].good_length;
if(!zip_FULL_SEARCH)
zip_nice_match = zip_configuration_table[zip_compr_level].nice_length;
zip_max_chain_length = zip_configuration_table[zip_compr_level].max_chain;

zip_strstart = 0;
zip_block_start = 0;

zip_lookahead = zip_read_buff(zip_window, 0, 2 * zip_WSIZE);
if(zip_lookahead <= 0) {
zip_eofile = true;
zip_lookahead = 0;
return;
}
zip_eofile = false;
/* Make sure that we always have enough lookahead. This is important
* if input comes from a device such as a tty.
*/
while(zip_lookahead < zip_MIN_LOOKAHEAD && !zip_eofile)
zip_fill_window();

/* If lookahead < MIN_MATCH, ins_h is garbage, but this is

* not important since only literal bytes will be emitted.
*/
zip_ins_h = 0;
for(j = 0; j < zip_MIN_MATCH - 1; j++) {
// UPDATE_HASH(ins_h, window[j]);
zip_ins_h = ((zip_ins_h << zip_H_SHIFT) ^ (zip_window[j] & 0xff)) & zip_HASH_MASK;
}
}

/* ==========================================================================
* 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
*/
function zip_longest_match(cur_match) {
var chain_length = zip_max_chain_length; // max hash chain length
var scanp = zip_strstart; // current string
var matchp; // matched string
var len; // length of current match
var best_len = zip_prev_length; // best match length so far

/* Stop when cur_match becomes <= limit. To simplify the code,
* we prevent matches with the string of window index 0.
*/
var limit = (zip_strstart > zip_MAX_DIST ? zip_strstart - zip_MAX_DIST : zip_NIL);

var strendp = zip_strstart + zip_MAX_MATCH;
var scan_end1 = zip_window[scanp + best_len - 1];
var scan_end = zip_window[scanp + best_len];

/* Do not waste too much time if we already have a good match: */
if(zip_prev_length >= zip_good_match)
chain_length >>= 2;

// Assert(encoder->strstart <= window_size-MIN_LOOKAHEAD, "insufficient lookahead");

do {
// Assert(cur_match < encoder->strstart, "no future");
matchp = cur_match;

/* Skip to next match if the match length cannot increase
* or if the match length is less than 2:
*/
if(zip_window[matchp + best_len] != scan_end ||
zip_window[matchp + best_len - 1] != scan_end1 ||
zip_window[matchp] != zip_window[scanp] ||
zip_window[++matchp] != zip_window[scanp + 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.
*/
scanp += 2;
matchp++;

/* We check for insufficient lookahead only every 8th comparison;
* the 256th check will be made at strstart+258.
*/
do {
} while(zip_window[++scanp] == zip_window[++matchp] &&
zip_window[++scanp] == zip_window[++matchp] &&
zip_window[++scanp] == zip_window[++matchp] &&
zip_window[++scanp] == zip_window[++matchp] &&
zip_window[++scanp] == zip_window[++matchp] &&
zip_window[++scanp] == zip_window[++matchp] &&
zip_window[++scanp] == zip_window[++matchp] &&
zip_window[++scanp] == zip_window[++matchp] &&
scanp < strendp);

len = zip_MAX_MATCH - (strendp - scanp);
scanp = strendp - zip_MAX_MATCH;

if(len > best_len) {
zip_match_start = cur_match;
best_len = len;
if(zip_FULL_SEARCH) {
if(len >= zip_MAX_MATCH) break;
} else {
if(len >= zip_nice_match) break;
}

scan_end1 = zip_window[scanp + best_len-1];
scan_end = zip_window[scanp + best_len];
}
} while((cur_match = zip_prev[cur_match & zip_WMASK]) > limit
&& --chain_length != 0);

return best_len;
}
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基础编程
创建于2007-09-28

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