Contents of /trunk/mkinitrd-magellan/klibc/usr/gzip/deflate.c
Parent Directory | Revision Log
Revision 815 -
(show annotations)
(download)
Fri Apr 24 18:32:46 2009 UTC (15 years ago) by niro
File MIME type: text/plain
File size: 28994 byte(s)
Fri Apr 24 18:32:46 2009 UTC (15 years ago) by niro
File MIME type: text/plain
File size: 28994 byte(s)
-updated to klibc-1.5.15
1 | /* deflate.c -- compress data using the deflation algorithm |
2 | * Copyright (C) 1992-1993 Jean-loup Gailly |
3 | * This is free software; you can redistribute it and/or modify it under the |
4 | * terms of the GNU General Public License, see the file COPYING. |
5 | */ |
6 | |
7 | /* |
8 | * PURPOSE |
9 | * |
10 | * Identify new text as repetitions of old text within a fixed- |
11 | * length sliding window trailing behind the new text. |
12 | * |
13 | * DISCUSSION |
14 | * |
15 | * The "deflation" process depends on being able to identify portions |
16 | * of the input text which are identical to earlier input (within a |
17 | * sliding window trailing behind the input currently being processed). |
18 | * |
19 | * The most straightforward technique turns out to be the fastest for |
20 | * most input files: try all possible matches and select the longest. |
21 | * The key feature of this algorithm is that insertions into the string |
22 | * dictionary are very simple and thus fast, and deletions are avoided |
23 | * completely. Insertions are performed at each input character, whereas |
24 | * string matches are performed only when the previous match ends. So it |
25 | * is preferable to spend more time in matches to allow very fast string |
26 | * insertions and avoid deletions. The matching algorithm for small |
27 | * strings is inspired from that of Rabin & Karp. A brute force approach |
28 | * is used to find longer strings when a small match has been found. |
29 | * A similar algorithm is used in comic (by Jan-Mark Wams) and freeze |
30 | * (by Leonid Broukhis). |
31 | * A previous version of this file used a more sophisticated algorithm |
32 | * (by Fiala and Greene) which is guaranteed to run in linear amortized |
33 | * time, but has a larger average cost, uses more memory and is patented. |
34 | * However the F&G algorithm may be faster for some highly redundant |
35 | * files if the parameter max_chain_length (described below) is too large. |
36 | * |
37 | * ACKNOWLEDGEMENTS |
38 | * |
39 | * The idea of lazy evaluation of matches is due to Jan-Mark Wams, and |
40 | * I found it in 'freeze' written by Leonid Broukhis. |
41 | * Thanks to many info-zippers for bug reports and testing. |
42 | * |
43 | * REFERENCES |
44 | * |
45 | * APPNOTE.TXT documentation file in PKZIP 1.93a distribution. |
46 | * |
47 | * A description of the Rabin and Karp algorithm is given in the book |
48 | * "Algorithms" by R. Sedgewick, Addison-Wesley, p252. |
49 | * |
50 | * Fiala,E.R., and Greene,D.H. |
51 | * Data Compression with Finite Windows, Comm.ACM, 32,4 (1989) 490-595 |
52 | * |
53 | * INTERFACE |
54 | * |
55 | * void lm_init (int pack_level, ush *flags) |
56 | * Initialize the "longest match" routines for a new file |
57 | * |
58 | * ulg deflate (void) |
59 | * Processes a new input file and return its compressed length. Sets |
60 | * the compressed length, crc, deflate flags and internal file |
61 | * attributes. |
62 | */ |
63 | |
64 | #include <stdio.h> |
65 | |
66 | #include "tailor.h" |
67 | #include "gzip.h" |
68 | |
69 | #ifdef RCSID |
70 | static char rcsid[] = "$Id: deflate.c,v 1.1 2002/08/18 00:59:21 hpa Exp $"; |
71 | #endif |
72 | |
73 | /* =========================================================================== |
74 | * Configuration parameters |
75 | */ |
76 | |
77 | /* Compile with MEDIUM_MEM to reduce the memory requirements or |
78 | * with SMALL_MEM to use as little memory as possible. Use BIG_MEM if the |
79 | * entire input file can be held in memory (not possible on 16 bit systems). |
80 | * Warning: defining these symbols affects HASH_BITS (see below) and thus |
81 | * affects the compression ratio. The compressed output |
82 | * is still correct, and might even be smaller in some cases. |
83 | */ |
84 | |
85 | #ifdef SMALL_MEM |
86 | # define HASH_BITS 13 /* Number of bits used to hash strings */ |
87 | #endif |
88 | #ifdef MEDIUM_MEM |
89 | # define HASH_BITS 14 |
90 | #endif |
91 | #ifndef HASH_BITS |
92 | # define HASH_BITS 15 |
93 | /* For portability to 16 bit machines, do not use values above 15. */ |
94 | #endif |
95 | |
96 | /* To save space (see unlzw.c), we overlay prev+head with tab_prefix and |
97 | * window with tab_suffix. Check that we can do this: |
98 | */ |
99 | #if (WSIZE<<1) > (1<<BITS) |
100 | error: cannot overlay window with tab_suffix and prev with tab_prefix0 |
101 | #endif |
102 | #if HASH_BITS > BITS-1 |
103 | error: cannot overlay head with tab_prefix1 |
104 | #endif |
105 | |
106 | #define HASH_SIZE (unsigned)(1<<HASH_BITS) |
107 | #define HASH_MASK (HASH_SIZE-1) |
108 | #define WMASK (WSIZE-1) |
109 | /* HASH_SIZE and WSIZE must be powers of two */ |
110 | |
111 | #define NIL 0 |
112 | /* Tail of hash chains */ |
113 | |
114 | #define FAST 4 |
115 | #define SLOW 2 |
116 | /* speed options for the general purpose bit flag */ |
117 | |
118 | #ifndef TOO_FAR |
119 | # define TOO_FAR 4096 |
120 | #endif |
121 | /* Matches of length 3 are discarded if their distance exceeds TOO_FAR */ |
122 | |
123 | /* =========================================================================== |
124 | * Local data used by the "longest match" routines. |
125 | */ |
126 | |
127 | typedef ush Pos; |
128 | typedef unsigned IPos; |
129 | /* A Pos is an index in the character window. We use short instead of int to |
130 | * save space in the various tables. IPos is used only for parameter passing. |
131 | */ |
132 | |
133 | /* DECLARE(uch, window, 2L*WSIZE); */ |
134 | /* Sliding window. Input bytes are read into the second half of the window, |
135 | * and move to the first half later to keep a dictionary of at least WSIZE |
136 | * bytes. With this organization, matches are limited to a distance of |
137 | * WSIZE-MAX_MATCH bytes, but this ensures that IO is always |
138 | * performed with a length multiple of the block size. Also, it limits |
139 | * the window size to 64K, which is quite useful on MSDOS. |
140 | * To do: limit the window size to WSIZE+BSZ if SMALL_MEM (the code would |
141 | * be less efficient). |
142 | */ |
143 | |
144 | /* DECLARE(Pos, prev, WSIZE); */ |
145 | /* Link to older string with same hash index. To limit the size of this |
146 | * array to 64K, this link is maintained only for the last 32K strings. |
147 | * An index in this array is thus a window index modulo 32K. |
148 | */ |
149 | |
150 | /* DECLARE(Pos, head, 1<<HASH_BITS); */ |
151 | /* Heads of the hash chains or NIL. */ |
152 | |
153 | ulg window_size = (ulg)2*WSIZE; |
154 | /* window size, 2*WSIZE except for MMAP or BIG_MEM, where it is the |
155 | * input file length plus MIN_LOOKAHEAD. |
156 | */ |
157 | |
158 | long block_start; |
159 | /* window position at the beginning of the current output block. Gets |
160 | * negative when the window is moved backwards. |
161 | */ |
162 | |
163 | local unsigned ins_h; /* hash index of string to be inserted */ |
164 | |
165 | #define H_SHIFT ((HASH_BITS+MIN_MATCH-1)/MIN_MATCH) |
166 | /* Number of bits by which ins_h and del_h must be shifted at each |
167 | * input step. It must be such that after MIN_MATCH steps, the oldest |
168 | * byte no longer takes part in the hash key, that is: |
169 | * H_SHIFT * MIN_MATCH >= HASH_BITS |
170 | */ |
171 | |
172 | unsigned int prev_length; |
173 | /* Length of the best match at previous step. Matches not greater than this |
174 | * are discarded. This is used in the lazy match evaluation. |
175 | */ |
176 | |
177 | unsigned strstart; /* start of string to insert */ |
178 | unsigned match_start; /* start of matching string */ |
179 | local int eofile; /* flag set at end of input file */ |
180 | local unsigned lookahead; /* number of valid bytes ahead in window */ |
181 | |
182 | unsigned max_chain_length; |
183 | /* To speed up deflation, hash chains are never searched beyond this length. |
184 | * A higher limit improves compression ratio but degrades the speed. |
185 | */ |
186 | |
187 | local unsigned int max_lazy_match; |
188 | /* Attempt to find a better match only when the current match is strictly |
189 | * smaller than this value. This mechanism is used only for compression |
190 | * levels >= 4. |
191 | */ |
192 | #define max_insert_length max_lazy_match |
193 | /* Insert new strings in the hash table only if the match length |
194 | * is not greater than this length. This saves time but degrades compression. |
195 | * max_insert_length is used only for compression levels <= 3. |
196 | */ |
197 | |
198 | local int compr_level; |
199 | /* compression level (1..9) */ |
200 | |
201 | unsigned good_match; |
202 | /* Use a faster search when the previous match is longer than this */ |
203 | |
204 | |
205 | /* Values for max_lazy_match, good_match and max_chain_length, depending on |
206 | * the desired pack level (0..9). The values given below have been tuned to |
207 | * exclude worst case performance for pathological files. Better values may be |
208 | * found for specific files. |
209 | */ |
210 | |
211 | typedef struct config { |
212 | ush good_length; /* reduce lazy search above this match length */ |
213 | ush max_lazy; /* do not perform lazy search above this match length */ |
214 | ush nice_length; /* quit search above this match length */ |
215 | ush max_chain; |
216 | } config; |
217 | |
218 | #ifdef FULL_SEARCH |
219 | # define nice_match MAX_MATCH |
220 | #else |
221 | int nice_match; /* Stop searching when current match exceeds this */ |
222 | #endif |
223 | |
224 | local config configuration_table[10] = { |
225 | /* good lazy nice chain */ |
226 | /* 0 */ {0, 0, 0, 0}, /* store only */ |
227 | /* 1 */ {4, 4, 8, 4}, /* maximum speed, no lazy matches */ |
228 | /* 2 */ {4, 5, 16, 8}, |
229 | /* 3 */ {4, 6, 32, 32}, |
230 | |
231 | /* 4 */ {4, 4, 16, 16}, /* lazy matches */ |
232 | /* 5 */ {8, 16, 32, 32}, |
233 | /* 6 */ {8, 16, 128, 128}, |
234 | /* 7 */ {8, 32, 128, 256}, |
235 | /* 8 */ {32, 128, 258, 1024}, |
236 | /* 9 */ {32, 258, 258, 4096}}; /* maximum compression */ |
237 | |
238 | /* Note: the deflate() code requires max_lazy >= MIN_MATCH and max_chain >= 4 |
239 | * For deflate_fast() (levels <= 3) good is ignored and lazy has a different |
240 | * meaning. |
241 | */ |
242 | |
243 | #define EQUAL 0 |
244 | /* result of memcmp for equal strings */ |
245 | |
246 | /* =========================================================================== |
247 | * Prototypes for local functions. |
248 | */ |
249 | local void fill_window OF((void)); |
250 | local ulg deflate_fast OF((void)); |
251 | |
252 | int longest_match OF((IPos cur_match)); |
253 | #ifdef ASMV |
254 | void match_init OF((void)); /* asm code initialization */ |
255 | #endif |
256 | |
257 | #ifdef DEBUG |
258 | local void check_match OF((IPos start, IPos match, int length)); |
259 | #endif |
260 | |
261 | /* =========================================================================== |
262 | * Update a hash value with the given input byte |
263 | * IN assertion: all calls to to UPDATE_HASH are made with consecutive |
264 | * input characters, so that a running hash key can be computed from the |
265 | * previous key instead of complete recalculation each time. |
266 | */ |
267 | #define UPDATE_HASH(h,c) (h = (((h)<<H_SHIFT) ^ (c)) & HASH_MASK) |
268 | |
269 | /* =========================================================================== |
270 | * Insert string s in the dictionary and set match_head to the previous head |
271 | * of the hash chain (the most recent string with same hash key). Return |
272 | * the previous length of the hash chain. |
273 | * IN assertion: all calls to to INSERT_STRING are made with consecutive |
274 | * input characters and the first MIN_MATCH bytes of s are valid |
275 | * (except for the last MIN_MATCH-1 bytes of the input file). |
276 | */ |
277 | #define INSERT_STRING(s, match_head) \ |
278 | (UPDATE_HASH(ins_h, window[(s) + MIN_MATCH-1]), \ |
279 | prev[(s) & WMASK] = match_head = head[ins_h], \ |
280 | head[ins_h] = (s)) |
281 | |
282 | /* =========================================================================== |
283 | * Initialize the "longest match" routines for a new file |
284 | */ |
285 | void lm_init (pack_level, flags) |
286 | int pack_level; /* 0: store, 1: best speed, 9: best compression */ |
287 | ush *flags; /* general purpose bit flag */ |
288 | { |
289 | register unsigned j; |
290 | |
291 | if (pack_level < 1 || pack_level > 9) error("bad pack level"); |
292 | compr_level = pack_level; |
293 | |
294 | /* Initialize the hash table. */ |
295 | memzero((char*)head, HASH_SIZE*sizeof(*head)); |
296 | |
297 | /* prev will be initialized on the fly */ |
298 | |
299 | /* Set the default configuration parameters: |
300 | */ |
301 | max_lazy_match = configuration_table[pack_level].max_lazy; |
302 | good_match = configuration_table[pack_level].good_length; |
303 | #ifndef FULL_SEARCH |
304 | nice_match = configuration_table[pack_level].nice_length; |
305 | #endif |
306 | max_chain_length = configuration_table[pack_level].max_chain; |
307 | if (pack_level == 1) { |
308 | *flags |= FAST; |
309 | } else if (pack_level == 9) { |
310 | *flags |= SLOW; |
311 | } |
312 | /* ??? reduce max_chain_length for binary files */ |
313 | |
314 | strstart = 0; |
315 | block_start = 0L; |
316 | #ifdef ASMV |
317 | match_init(); /* initialize the asm code */ |
318 | #endif |
319 | |
320 | lookahead = read_buf((char*)window, |
321 | sizeof(int) <= 2 ? (unsigned)WSIZE : 2*WSIZE); |
322 | |
323 | if (lookahead == 0 || lookahead == (unsigned)EOF) { |
324 | eofile = 1, lookahead = 0; |
325 | return; |
326 | } |
327 | eofile = 0; |
328 | /* Make sure that we always have enough lookahead. This is important |
329 | * if input comes from a device such as a tty. |
330 | */ |
331 | while (lookahead < MIN_LOOKAHEAD && !eofile) fill_window(); |
332 | |
333 | ins_h = 0; |
334 | for (j=0; j<MIN_MATCH-1; j++) UPDATE_HASH(ins_h, window[j]); |
335 | /* If lookahead < MIN_MATCH, ins_h is garbage, but this is |
336 | * not important since only literal bytes will be emitted. |
337 | */ |
338 | } |
339 | |
340 | /* =========================================================================== |
341 | * Set match_start to the longest match starting at the given string and |
342 | * return its length. Matches shorter or equal to prev_length are discarded, |
343 | * in which case the result is equal to prev_length and match_start is |
344 | * garbage. |
345 | * IN assertions: cur_match is the head of the hash chain for the current |
346 | * string (strstart) and its distance is <= MAX_DIST, and prev_length >= 1 |
347 | */ |
348 | #ifndef ASMV |
349 | /* For MSDOS, OS/2 and 386 Unix, an optimized version is in match.asm or |
350 | * match.s. The code is functionally equivalent, so you can use the C version |
351 | * if desired. |
352 | */ |
353 | int longest_match(cur_match) |
354 | IPos cur_match; /* current match */ |
355 | { |
356 | unsigned chain_length = max_chain_length; /* max hash chain length */ |
357 | register uch *scan = window + strstart; /* current string */ |
358 | register uch *match; /* matched string */ |
359 | register int len; /* length of current match */ |
360 | int best_len = prev_length; /* best match length so far */ |
361 | IPos limit = strstart > (IPos)MAX_DIST ? strstart - (IPos)MAX_DIST : NIL; |
362 | /* Stop when cur_match becomes <= limit. To simplify the code, |
363 | * we prevent matches with the string of window index 0. |
364 | */ |
365 | |
366 | /* The code is optimized for HASH_BITS >= 8 and MAX_MATCH-2 multiple of 16. |
367 | * It is easy to get rid of this optimization if necessary. |
368 | */ |
369 | #if HASH_BITS < 8 || MAX_MATCH != 258 |
370 | error: Code too clever |
371 | #endif |
372 | |
373 | #ifdef UNALIGNED_OK |
374 | /* Compare two bytes at a time. Note: this is not always beneficial. |
375 | * Try with and without -DUNALIGNED_OK to check. |
376 | */ |
377 | register uch *strend = window + strstart + MAX_MATCH - 1; |
378 | register ush scan_start = *(ush*)scan; |
379 | register ush scan_end = *(ush*)(scan+best_len-1); |
380 | #else |
381 | register uch *strend = window + strstart + MAX_MATCH; |
382 | register uch scan_end1 = scan[best_len-1]; |
383 | register uch scan_end = scan[best_len]; |
384 | #endif |
385 | |
386 | /* Do not waste too much time if we already have a good match: */ |
387 | if (prev_length >= good_match) { |
388 | chain_length >>= 2; |
389 | } |
390 | Assert(strstart <= window_size-MIN_LOOKAHEAD, "insufficient lookahead"); |
391 | |
392 | do { |
393 | Assert(cur_match < strstart, "no future"); |
394 | match = window + cur_match; |
395 | |
396 | /* Skip to next match if the match length cannot increase |
397 | * or if the match length is less than 2: |
398 | */ |
399 | #if (defined(UNALIGNED_OK) && MAX_MATCH == 258) |
400 | /* This code assumes sizeof(unsigned short) == 2. Do not use |
401 | * UNALIGNED_OK if your compiler uses a different size. |
402 | */ |
403 | if (*(ush*)(match+best_len-1) != scan_end || |
404 | *(ush*)match != scan_start) continue; |
405 | |
406 | /* It is not necessary to compare scan[2] and match[2] since they are |
407 | * always equal when the other bytes match, given that the hash keys |
408 | * are equal and that HASH_BITS >= 8. Compare 2 bytes at a time at |
409 | * strstart+3, +5, ... up to strstart+257. We check for insufficient |
410 | * lookahead only every 4th comparison; the 128th check will be made |
411 | * at strstart+257. If MAX_MATCH-2 is not a multiple of 8, it is |
412 | * necessary to put more guard bytes at the end of the window, or |
413 | * to check more often for insufficient lookahead. |
414 | */ |
415 | scan++, match++; |
416 | do { |
417 | } while (*(ush*)(scan+=2) == *(ush*)(match+=2) && |
418 | *(ush*)(scan+=2) == *(ush*)(match+=2) && |
419 | *(ush*)(scan+=2) == *(ush*)(match+=2) && |
420 | *(ush*)(scan+=2) == *(ush*)(match+=2) && |
421 | scan < strend); |
422 | /* The funny "do {}" generates better code on most compilers */ |
423 | |
424 | /* Here, scan <= window+strstart+257 */ |
425 | Assert(scan <= window+(unsigned)(window_size-1), "wild scan"); |
426 | if (*scan == *match) scan++; |
427 | |
428 | len = (MAX_MATCH - 1) - (int)(strend-scan); |
429 | scan = strend - (MAX_MATCH-1); |
430 | |
431 | #else /* UNALIGNED_OK */ |
432 | |
433 | if (match[best_len] != scan_end || |
434 | match[best_len-1] != scan_end1 || |
435 | *match != *scan || |
436 | *++match != scan[1]) continue; |
437 | |
438 | /* The check at best_len-1 can be removed because it will be made |
439 | * again later. (This heuristic is not always a win.) |
440 | * It is not necessary to compare scan[2] and match[2] since they |
441 | * are always equal when the other bytes match, given that |
442 | * the hash keys are equal and that HASH_BITS >= 8. |
443 | */ |
444 | scan += 2, match++; |
445 | |
446 | /* We check for insufficient lookahead only every 8th comparison; |
447 | * the 256th check will be made at strstart+258. |
448 | */ |
449 | do { |
450 | } while (*++scan == *++match && *++scan == *++match && |
451 | *++scan == *++match && *++scan == *++match && |
452 | *++scan == *++match && *++scan == *++match && |
453 | *++scan == *++match && *++scan == *++match && |
454 | scan < strend); |
455 | |
456 | len = MAX_MATCH - (int)(strend - scan); |
457 | scan = strend - MAX_MATCH; |
458 | |
459 | #endif /* UNALIGNED_OK */ |
460 | |
461 | if (len > best_len) { |
462 | match_start = cur_match; |
463 | best_len = len; |
464 | if (len >= nice_match) break; |
465 | #ifdef UNALIGNED_OK |
466 | scan_end = *(ush*)(scan+best_len-1); |
467 | #else |
468 | scan_end1 = scan[best_len-1]; |
469 | scan_end = scan[best_len]; |
470 | #endif |
471 | } |
472 | } while ((cur_match = prev[cur_match & WMASK]) > limit |
473 | && --chain_length != 0); |
474 | |
475 | return best_len; |
476 | } |
477 | #endif /* ASMV */ |
478 | |
479 | #ifdef DEBUG |
480 | /* =========================================================================== |
481 | * Check that the match at match_start is indeed a match. |
482 | */ |
483 | local void check_match(start, match, length) |
484 | IPos start, match; |
485 | int length; |
486 | { |
487 | /* check that the match is indeed a match */ |
488 | if (memcmp((char*)window + match, |
489 | (char*)window + start, length) != EQUAL) { |
490 | fprintf(stderr, |
491 | " start %d, match %d, length %d\n", |
492 | start, match, length); |
493 | error("invalid match"); |
494 | } |
495 | if (verbose > 1) { |
496 | fprintf(stderr,"\\[%d,%d]", start-match, length); |
497 | do { putc(window[start++], stderr); } while (--length != 0); |
498 | } |
499 | } |
500 | #else |
501 | # define check_match(start, match, length) |
502 | #endif |
503 | |
504 | /* =========================================================================== |
505 | * Fill the window when the lookahead becomes insufficient. |
506 | * Updates strstart and lookahead, and sets eofile if end of input file. |
507 | * IN assertion: lookahead < MIN_LOOKAHEAD && strstart + lookahead > 0 |
508 | * OUT assertions: at least one byte has been read, or eofile is set; |
509 | * file reads are performed for at least two bytes (required for the |
510 | * translate_eol option). |
511 | */ |
512 | local void fill_window() |
513 | { |
514 | register unsigned n, m; |
515 | unsigned more = (unsigned)(window_size - (ulg)lookahead - (ulg)strstart); |
516 | /* Amount of free space at the end of the window. */ |
517 | |
518 | /* If the window is almost full and there is insufficient lookahead, |
519 | * move the upper half to the lower one to make room in the upper half. |
520 | */ |
521 | if (more == (unsigned)EOF) { |
522 | /* Very unlikely, but possible on 16 bit machine if strstart == 0 |
523 | * and lookahead == 1 (input done one byte at time) |
524 | */ |
525 | more--; |
526 | } else if (strstart >= WSIZE+MAX_DIST) { |
527 | /* By the IN assertion, the window is not empty so we can't confuse |
528 | * more == 0 with more == 64K on a 16 bit machine. |
529 | */ |
530 | Assert(window_size == (ulg)2*WSIZE, "no sliding with BIG_MEM"); |
531 | |
532 | memcpy((char*)window, (char*)window+WSIZE, (unsigned)WSIZE); |
533 | match_start -= WSIZE; |
534 | strstart -= WSIZE; /* we now have strstart >= MAX_DIST: */ |
535 | |
536 | block_start -= (long) WSIZE; |
537 | |
538 | for (n = 0; n < HASH_SIZE; n++) { |
539 | m = head[n]; |
540 | head[n] = (Pos)(m >= WSIZE ? m-WSIZE : NIL); |
541 | } |
542 | for (n = 0; n < WSIZE; n++) { |
543 | m = prev[n]; |
544 | prev[n] = (Pos)(m >= WSIZE ? m-WSIZE : NIL); |
545 | /* If n is not on any hash chain, prev[n] is garbage but |
546 | * its value will never be used. |
547 | */ |
548 | } |
549 | more += WSIZE; |
550 | } |
551 | /* At this point, more >= 2 */ |
552 | if (!eofile) { |
553 | n = read_buf((char*)window+strstart+lookahead, more); |
554 | if (n == 0 || n == (unsigned)EOF) { |
555 | eofile = 1; |
556 | } else { |
557 | lookahead += n; |
558 | } |
559 | } |
560 | } |
561 | |
562 | /* =========================================================================== |
563 | * Flush the current block, with given end-of-file flag. |
564 | * IN assertion: strstart is set to the end of the current match. |
565 | */ |
566 | #define FLUSH_BLOCK(eof) \ |
567 | flush_block(block_start >= 0L ? (char*)&window[(unsigned)block_start] : \ |
568 | (char*)NULL, (long)strstart - block_start, (eof)) |
569 | |
570 | /* =========================================================================== |
571 | * Processes a new input file and return its compressed length. This |
572 | * function does not perform lazy evaluationof matches and inserts |
573 | * new strings in the dictionary only for unmatched strings or for short |
574 | * matches. It is used only for the fast compression options. |
575 | */ |
576 | local ulg deflate_fast() |
577 | { |
578 | IPos hash_head; /* head of the hash chain */ |
579 | int flush; /* set if current block must be flushed */ |
580 | unsigned match_length = 0; /* length of best match */ |
581 | |
582 | prev_length = MIN_MATCH-1; |
583 | while (lookahead != 0) { |
584 | /* Insert the string window[strstart .. strstart+2] in the |
585 | * dictionary, and set hash_head to the head of the hash chain: |
586 | */ |
587 | INSERT_STRING(strstart, hash_head); |
588 | |
589 | /* Find the longest match, discarding those <= prev_length. |
590 | * At this point we have always match_length < MIN_MATCH |
591 | */ |
592 | if (hash_head != NIL && strstart - hash_head <= MAX_DIST) { |
593 | /* To simplify the code, we prevent matches with the string |
594 | * of window index 0 (in particular we have to avoid a match |
595 | * of the string with itself at the start of the input file). |
596 | */ |
597 | match_length = longest_match (hash_head); |
598 | /* longest_match() sets match_start */ |
599 | if (match_length > lookahead) match_length = lookahead; |
600 | } |
601 | if (match_length >= MIN_MATCH) { |
602 | check_match(strstart, match_start, match_length); |
603 | |
604 | flush = ct_tally(strstart-match_start, match_length - MIN_MATCH); |
605 | |
606 | lookahead -= match_length; |
607 | |
608 | /* Insert new strings in the hash table only if the match length |
609 | * is not too large. This saves time but degrades compression. |
610 | */ |
611 | if (match_length <= max_insert_length) { |
612 | match_length--; /* string at strstart already in hash table */ |
613 | do { |
614 | strstart++; |
615 | INSERT_STRING(strstart, hash_head); |
616 | /* strstart never exceeds WSIZE-MAX_MATCH, so there are |
617 | * always MIN_MATCH bytes ahead. If lookahead < MIN_MATCH |
618 | * these bytes are garbage, but it does not matter since |
619 | * the next lookahead bytes will be emitted as literals. |
620 | */ |
621 | } while (--match_length != 0); |
622 | strstart++; |
623 | } else { |
624 | strstart += match_length; |
625 | match_length = 0; |
626 | ins_h = window[strstart]; |
627 | UPDATE_HASH(ins_h, window[strstart+1]); |
628 | #if MIN_MATCH != 3 |
629 | Call UPDATE_HASH() MIN_MATCH-3 more times |
630 | #endif |
631 | } |
632 | } else { |
633 | /* No match, output a literal byte */ |
634 | Tracevv((stderr,"%c",window[strstart])); |
635 | flush = ct_tally (0, window[strstart]); |
636 | lookahead--; |
637 | strstart++; |
638 | } |
639 | if (flush) FLUSH_BLOCK(0), block_start = strstart; |
640 | |
641 | /* Make sure that we always have enough lookahead, except |
642 | * at the end of the input file. We need MAX_MATCH bytes |
643 | * for the next match, plus MIN_MATCH bytes to insert the |
644 | * string following the next match. |
645 | */ |
646 | while (lookahead < MIN_LOOKAHEAD && !eofile) fill_window(); |
647 | |
648 | } |
649 | return FLUSH_BLOCK(1); /* eof */ |
650 | } |
651 | |
652 | /* =========================================================================== |
653 | * Same as above, but achieves better compression. We use a lazy |
654 | * evaluation for matches: a match is finally adopted only if there is |
655 | * no better match at the next window position. |
656 | */ |
657 | ulg deflate() |
658 | { |
659 | IPos hash_head; /* head of hash chain */ |
660 | IPos prev_match; /* previous match */ |
661 | int flush; /* set if current block must be flushed */ |
662 | int match_available = 0; /* set if previous match exists */ |
663 | register unsigned match_length = MIN_MATCH-1; /* length of best match */ |
664 | #ifdef DEBUG |
665 | extern long isize; /* byte length of input file, for debug only */ |
666 | #endif |
667 | |
668 | if (compr_level <= 3) return deflate_fast(); /* optimized for speed */ |
669 | |
670 | /* Process the input block. */ |
671 | while (lookahead != 0) { |
672 | /* Insert the string window[strstart .. strstart+2] in the |
673 | * dictionary, and set hash_head to the head of the hash chain: |
674 | */ |
675 | INSERT_STRING(strstart, hash_head); |
676 | |
677 | /* Find the longest match, discarding those <= prev_length. |
678 | */ |
679 | prev_length = match_length, prev_match = match_start; |
680 | match_length = MIN_MATCH-1; |
681 | |
682 | if (hash_head != NIL && prev_length < max_lazy_match && |
683 | strstart - hash_head <= MAX_DIST) { |
684 | /* To simplify the code, we prevent matches with the string |
685 | * of window index 0 (in particular we have to avoid a match |
686 | * of the string with itself at the start of the input file). |
687 | */ |
688 | match_length = longest_match (hash_head); |
689 | /* longest_match() sets match_start */ |
690 | if (match_length > lookahead) match_length = lookahead; |
691 | |
692 | /* Ignore a length 3 match if it is too distant: */ |
693 | if (match_length == MIN_MATCH && strstart-match_start > TOO_FAR){ |
694 | /* If prev_match is also MIN_MATCH, match_start is garbage |
695 | * but we will ignore the current match anyway. |
696 | */ |
697 | match_length--; |
698 | } |
699 | } |
700 | /* If there was a match at the previous step and the current |
701 | * match is not better, output the previous match: |
702 | */ |
703 | if (prev_length >= MIN_MATCH && match_length <= prev_length) { |
704 | |
705 | check_match(strstart-1, prev_match, prev_length); |
706 | |
707 | flush = ct_tally(strstart-1-prev_match, prev_length - MIN_MATCH); |
708 | |
709 | /* Insert in hash table all strings up to the end of the match. |
710 | * strstart-1 and strstart are already inserted. |
711 | */ |
712 | lookahead -= prev_length-1; |
713 | prev_length -= 2; |
714 | do { |
715 | strstart++; |
716 | INSERT_STRING(strstart, hash_head); |
717 | /* strstart never exceeds WSIZE-MAX_MATCH, so there are |
718 | * always MIN_MATCH bytes ahead. If lookahead < MIN_MATCH |
719 | * these bytes are garbage, but it does not matter since the |
720 | * next lookahead bytes will always be emitted as literals. |
721 | */ |
722 | } while (--prev_length != 0); |
723 | match_available = 0; |
724 | match_length = MIN_MATCH-1; |
725 | strstart++; |
726 | if (flush) FLUSH_BLOCK(0), block_start = strstart; |
727 | |
728 | } else if (match_available) { |
729 | /* If there was no match at the previous position, output a |
730 | * single literal. If there was a match but the current match |
731 | * is longer, truncate the previous match to a single literal. |
732 | */ |
733 | Tracevv((stderr,"%c",window[strstart-1])); |
734 | if (ct_tally (0, window[strstart-1])) { |
735 | FLUSH_BLOCK(0), block_start = strstart; |
736 | } |
737 | strstart++; |
738 | lookahead--; |
739 | } else { |
740 | /* There is no previous match to compare with, wait for |
741 | * the next step to decide. |
742 | */ |
743 | match_available = 1; |
744 | strstart++; |
745 | lookahead--; |
746 | } |
747 | Assert (strstart <= isize && lookahead <= isize, "a bit too far"); |
748 | |
749 | /* Make sure that we always have enough lookahead, except |
750 | * at the end of the input file. We need MAX_MATCH bytes |
751 | * for the next match, plus MIN_MATCH bytes to insert the |
752 | * string following the next match. |
753 | */ |
754 | while (lookahead < MIN_LOOKAHEAD && !eofile) fill_window(); |
755 | } |
756 | if (match_available) ct_tally (0, window[strstart-1]); |
757 | |
758 | return FLUSH_BLOCK(1); /* eof */ |
759 | } |