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[gzip.git] / trees.c
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1 /* trees.c -- output deflated data using Huffman coding
3 Copyright (C) 1997-1999, 2009-2011 Free Software Foundation, Inc.
4 Copyright (C) 1992-1993 Jean-loup Gailly
6 This program is free software; you can redistribute it and/or modify
7 it under the terms of the GNU General Public License as published by
8 the Free Software Foundation; either version 3, or (at your option)
9 any later version.
11 This program is distributed in the hope that it will be useful,
12 but WITHOUT ANY WARRANTY; without even the implied warranty of
13 MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
14 GNU General Public License for more details.
16 You should have received a copy of the GNU General Public License
17 along with this program; if not, write to the Free Software Foundation,
18 Inc., 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301, USA. */
21 * PURPOSE
23 * Encode various sets of source values using variable-length
24 * binary code trees.
26 * DISCUSSION
28 * The PKZIP "deflation" process uses several Huffman trees. The more
29 * common source values are represented by shorter bit sequences.
31 * Each code tree is stored in the ZIP file in a compressed form
32 * which is itself a Huffman encoding of the lengths of
33 * all the code strings (in ascending order by source values).
34 * The actual code strings are reconstructed from the lengths in
35 * the UNZIP process, as described in the "application note"
36 * (APPNOTE.TXT) distributed as part of PKWARE's PKZIP program.
38 * REFERENCES
40 * Lynch, Thomas J.
41 * Data Compression: Techniques and Applications, pp. 53-55.
42 * Lifetime Learning Publications, 1985. ISBN 0-534-03418-7.
44 * Storer, James A.
45 * Data Compression: Methods and Theory, pp. 49-50.
46 * Computer Science Press, 1988. ISBN 0-7167-8156-5.
48 * Sedgewick, R.
49 * Algorithms, p290.
50 * Addison-Wesley, 1983. ISBN 0-201-06672-6.
52 * INTERFACE
54 * void ct_init (ush *attr, int *methodp)
55 * Allocate the match buffer, initialize the various tables and save
56 * the location of the internal file attribute (ascii/binary) and
57 * method (DEFLATE/STORE)
59 * void ct_tally (int dist, int lc);
60 * Save the match info and tally the frequency counts.
62 * off_t flush_block (char *buf, ulg stored_len, int eof)
63 * Determine the best encoding for the current block: dynamic trees,
64 * static trees or store, and output the encoded block to the zip
65 * file. Returns the total compressed length for the file so far.
69 #include <config.h>
70 #include <ctype.h>
72 #include "tailor.h"
73 #include "gzip.h"
75 /* ===========================================================================
76 * Constants
79 #define MAX_BITS 15
80 /* All codes must not exceed MAX_BITS bits */
82 #define MAX_BL_BITS 7
83 /* Bit length codes must not exceed MAX_BL_BITS bits */
85 #define LENGTH_CODES 29
86 /* number of length codes, not counting the special END_BLOCK code */
88 #define LITERALS 256
89 /* number of literal bytes 0..255 */
91 #define END_BLOCK 256
92 /* end of block literal code */
94 #define L_CODES (LITERALS+1+LENGTH_CODES)
95 /* number of Literal or Length codes, including the END_BLOCK code */
97 #define D_CODES 30
98 /* number of distance codes */
100 #define BL_CODES 19
101 /* number of codes used to transfer the bit lengths */
104 local int near extra_lbits[LENGTH_CODES] /* extra bits for each length code */
105 = {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};
107 local int near extra_dbits[D_CODES] /* extra bits for each distance code */
108 = {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};
110 local int near extra_blbits[BL_CODES]/* extra bits for each bit length code */
111 = {0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,2,3,7};
113 #define STORED_BLOCK 0
114 #define STATIC_TREES 1
115 #define DYN_TREES 2
116 /* The three kinds of block type */
118 #ifndef LIT_BUFSIZE
119 # ifdef SMALL_MEM
120 # define LIT_BUFSIZE 0x2000
121 # else
122 # ifdef MEDIUM_MEM
123 # define LIT_BUFSIZE 0x4000
124 # else
125 # define LIT_BUFSIZE 0x8000
126 # endif
127 # endif
128 #endif
129 #ifndef DIST_BUFSIZE
130 # define DIST_BUFSIZE LIT_BUFSIZE
131 #endif
132 /* Sizes of match buffers for literals/lengths and distances. There are
133 * 4 reasons for limiting LIT_BUFSIZE to 64K:
134 * - frequencies can be kept in 16 bit counters
135 * - if compression is not successful for the first block, all input data is
136 * still in the window so we can still emit a stored block even when input
137 * comes from standard input. (This can also be done for all blocks if
138 * LIT_BUFSIZE is not greater than 32K.)
139 * - if compression is not successful for a file smaller than 64K, we can
140 * even emit a stored file instead of a stored block (saving 5 bytes).
141 * - creating new Huffman trees less frequently may not provide fast
142 * adaptation to changes in the input data statistics. (Take for
143 * example a binary file with poorly compressible code followed by
144 * a highly compressible string table.) Smaller buffer sizes give
145 * fast adaptation but have of course the overhead of transmitting trees
146 * more frequently.
147 * - I can't count above 4
148 * The current code is general and allows DIST_BUFSIZE < LIT_BUFSIZE (to save
149 * memory at the expense of compression). Some optimizations would be possible
150 * if we rely on DIST_BUFSIZE == LIT_BUFSIZE.
152 #if LIT_BUFSIZE > INBUFSIZ
153 error cannot overlay l_buf and inbuf
154 #endif
156 #define REP_3_6 16
157 /* repeat previous bit length 3-6 times (2 bits of repeat count) */
159 #define REPZ_3_10 17
160 /* repeat a zero length 3-10 times (3 bits of repeat count) */
162 #define REPZ_11_138 18
163 /* repeat a zero length 11-138 times (7 bits of repeat count) */
165 /* ===========================================================================
166 * Local data
169 /* Data structure describing a single value and its code string. */
170 typedef struct ct_data {
171 union {
172 ush freq; /* frequency count */
173 ush code; /* bit string */
174 } fc;
175 union {
176 ush dad; /* father node in Huffman tree */
177 ush len; /* length of bit string */
178 } dl;
179 } ct_data;
181 #define Freq fc.freq
182 #define Code fc.code
183 #define Dad dl.dad
184 #define Len dl.len
186 #define HEAP_SIZE (2*L_CODES+1)
187 /* maximum heap size */
189 local ct_data near dyn_ltree[HEAP_SIZE]; /* literal and length tree */
190 local ct_data near dyn_dtree[2*D_CODES+1]; /* distance tree */
192 local ct_data near static_ltree[L_CODES+2];
193 /* The static literal tree. Since the bit lengths are imposed, there is no
194 * need for the L_CODES extra codes used during heap construction. However
195 * The codes 286 and 287 are needed to build a canonical tree (see ct_init
196 * below).
199 local ct_data near static_dtree[D_CODES];
200 /* The static distance tree. (Actually a trivial tree since all codes use
201 * 5 bits.)
204 local ct_data near bl_tree[2*BL_CODES+1];
205 /* Huffman tree for the bit lengths */
207 typedef struct tree_desc {
208 ct_data near *dyn_tree; /* the dynamic tree */
209 ct_data near *static_tree; /* corresponding static tree or NULL */
210 int near *extra_bits; /* extra bits for each code or NULL */
211 int extra_base; /* base index for extra_bits */
212 int elems; /* max number of elements in the tree */
213 int max_length; /* max bit length for the codes */
214 int max_code; /* largest code with non zero frequency */
215 } tree_desc;
217 local tree_desc near l_desc =
218 {dyn_ltree, static_ltree, extra_lbits, LITERALS+1, L_CODES, MAX_BITS, 0};
220 local tree_desc near d_desc =
221 {dyn_dtree, static_dtree, extra_dbits, 0, D_CODES, MAX_BITS, 0};
223 local tree_desc near bl_desc =
224 {bl_tree, (ct_data near *)0, extra_blbits, 0, BL_CODES, MAX_BL_BITS, 0};
227 local ush near bl_count[MAX_BITS+1];
228 /* number of codes at each bit length for an optimal tree */
230 local uch near bl_order[BL_CODES]
231 = {16,17,18,0,8,7,9,6,10,5,11,4,12,3,13,2,14,1,15};
232 /* The lengths of the bit length codes are sent in order of decreasing
233 * probability, to avoid transmitting the lengths for unused bit length codes.
236 local int near heap[2*L_CODES+1]; /* heap used to build the Huffman trees */
237 local int heap_len; /* number of elements in the heap */
238 local int heap_max; /* element of largest frequency */
239 /* The sons of heap[n] are heap[2*n] and heap[2*n+1]. heap[0] is not used.
240 * The same heap array is used to build all trees.
243 local uch near depth[2*L_CODES+1];
244 /* Depth of each subtree used as tie breaker for trees of equal frequency */
246 local uch length_code[MAX_MATCH-MIN_MATCH+1];
247 /* length code for each normalized match length (0 == MIN_MATCH) */
249 local uch dist_code[512];
250 /* distance codes. The first 256 values correspond to the distances
251 * 3 .. 258, the last 256 values correspond to the top 8 bits of
252 * the 15 bit distances.
255 local int near base_length[LENGTH_CODES];
256 /* First normalized length for each code (0 = MIN_MATCH) */
258 local int near base_dist[D_CODES];
259 /* First normalized distance for each code (0 = distance of 1) */
261 #define l_buf inbuf
262 /* DECLARE(uch, l_buf, LIT_BUFSIZE); buffer for literals or lengths */
264 /* DECLARE(ush, d_buf, DIST_BUFSIZE); buffer for distances */
266 local uch near flag_buf[(LIT_BUFSIZE/8)];
267 /* flag_buf is a bit array distinguishing literals from lengths in
268 * l_buf, thus indicating the presence or absence of a distance.
271 local unsigned last_lit; /* running index in l_buf */
272 local unsigned last_dist; /* running index in d_buf */
273 local unsigned last_flags; /* running index in flag_buf */
274 local uch flags; /* current flags not yet saved in flag_buf */
275 local uch flag_bit; /* current bit used in flags */
276 /* bits are filled in flags starting at bit 0 (least significant).
277 * Note: these flags are overkill in the current code since we don't
278 * take advantage of DIST_BUFSIZE == LIT_BUFSIZE.
281 local ulg opt_len; /* bit length of current block with optimal trees */
282 local ulg static_len; /* bit length of current block with static trees */
284 local off_t compressed_len; /* total bit length of compressed file */
286 local off_t input_len; /* total byte length of input file */
287 /* input_len is for debugging only since we can get it by other means. */
289 ush *file_type; /* pointer to UNKNOWN, BINARY or ASCII */
290 int *file_method; /* pointer to DEFLATE or STORE */
292 #ifdef DEBUG
293 extern off_t bits_sent; /* bit length of the compressed data */
294 #endif
296 extern long block_start; /* window offset of current block */
297 extern unsigned near strstart; /* window offset of current string */
299 /* ===========================================================================
300 * Local (static) routines in this file.
303 local void init_block OF((void));
304 local void pqdownheap OF((ct_data near *tree, int k));
305 local void gen_bitlen OF((tree_desc near *desc));
306 local void gen_codes OF((ct_data near *tree, int max_code));
307 local void build_tree OF((tree_desc near *desc));
308 local void scan_tree OF((ct_data near *tree, int max_code));
309 local void send_tree OF((ct_data near *tree, int max_code));
310 local int build_bl_tree OF((void));
311 local void send_all_trees OF((int lcodes, int dcodes, int blcodes));
312 local void compress_block OF((ct_data near *ltree, ct_data near *dtree));
313 local void set_file_type OF((void));
316 #ifndef DEBUG
317 # define send_code(c, tree) send_bits(tree[c].Code, tree[c].Len)
318 /* Send a code of the given tree. c and tree must not have side effects */
320 #else /* DEBUG */
321 # define send_code(c, tree) \
322 { if (verbose>1) fprintf(stderr,"\ncd %3d ",(c)); \
323 send_bits(tree[c].Code, tree[c].Len); }
324 #endif
326 #define d_code(dist) \
327 ((dist) < 256 ? dist_code[dist] : dist_code[256+((dist)>>7)])
328 /* Mapping from a distance to a distance code. dist is the distance - 1 and
329 * must not have side effects. dist_code[256] and dist_code[257] are never
330 * used.
333 #define MAX(a,b) (a >= b ? a : b)
334 /* the arguments must not have side effects */
336 /* ===========================================================================
337 * Allocate the match buffer, initialize the various tables and save the
338 * location of the internal file attribute (ascii/binary) and method
339 * (DEFLATE/STORE).
341 void ct_init(attr, methodp)
342 ush *attr; /* pointer to internal file attribute */
343 int *methodp; /* pointer to compression method */
345 int n; /* iterates over tree elements */
346 int bits; /* bit counter */
347 int length; /* length value */
348 int code; /* code value */
349 int dist; /* distance index */
351 file_type = attr;
352 file_method = methodp;
353 compressed_len = input_len = 0L;
355 if (static_dtree[0].Len != 0) return; /* ct_init already called */
357 /* Initialize the mapping length (0..255) -> length code (0..28) */
358 length = 0;
359 for (code = 0; code < LENGTH_CODES-1; code++) {
360 base_length[code] = length;
361 for (n = 0; n < (1<<extra_lbits[code]); n++) {
362 length_code[length++] = (uch)code;
365 Assert (length == 256, "ct_init: length != 256");
366 /* Note that the length 255 (match length 258) can be represented
367 * in two different ways: code 284 + 5 bits or code 285, so we
368 * overwrite length_code[255] to use the best encoding:
370 length_code[length-1] = (uch)code;
372 /* Initialize the mapping dist (0..32K) -> dist code (0..29) */
373 dist = 0;
374 for (code = 0 ; code < 16; code++) {
375 base_dist[code] = dist;
376 for (n = 0; n < (1<<extra_dbits[code]); n++) {
377 dist_code[dist++] = (uch)code;
380 Assert (dist == 256, "ct_init: dist != 256");
381 dist >>= 7; /* from now on, all distances are divided by 128 */
382 for ( ; code < D_CODES; code++) {
383 base_dist[code] = dist << 7;
384 for (n = 0; n < (1<<(extra_dbits[code]-7)); n++) {
385 dist_code[256 + dist++] = (uch)code;
388 Assert (dist == 256, "ct_init: 256+dist != 512");
390 /* Construct the codes of the static literal tree */
391 for (bits = 0; bits <= MAX_BITS; bits++) bl_count[bits] = 0;
392 n = 0;
393 while (n <= 143) static_ltree[n++].Len = 8, bl_count[8]++;
394 while (n <= 255) static_ltree[n++].Len = 9, bl_count[9]++;
395 while (n <= 279) static_ltree[n++].Len = 7, bl_count[7]++;
396 while (n <= 287) static_ltree[n++].Len = 8, bl_count[8]++;
397 /* Codes 286 and 287 do not exist, but we must include them in the
398 * tree construction to get a canonical Huffman tree (longest code
399 * all ones)
401 gen_codes((ct_data near *)static_ltree, L_CODES+1);
403 /* The static distance tree is trivial: */
404 for (n = 0; n < D_CODES; n++) {
405 static_dtree[n].Len = 5;
406 static_dtree[n].Code = bi_reverse(n, 5);
409 /* Initialize the first block of the first file: */
410 init_block();
413 /* ===========================================================================
414 * Initialize a new block.
416 local void init_block()
418 int n; /* iterates over tree elements */
420 /* Initialize the trees. */
421 for (n = 0; n < L_CODES; n++) dyn_ltree[n].Freq = 0;
422 for (n = 0; n < D_CODES; n++) dyn_dtree[n].Freq = 0;
423 for (n = 0; n < BL_CODES; n++) bl_tree[n].Freq = 0;
425 dyn_ltree[END_BLOCK].Freq = 1;
426 opt_len = static_len = 0L;
427 last_lit = last_dist = last_flags = 0;
428 flags = 0; flag_bit = 1;
431 #define SMALLEST 1
432 /* Index within the heap array of least frequent node in the Huffman tree */
435 /* ===========================================================================
436 * Remove the smallest element from the heap and recreate the heap with
437 * one less element. Updates heap and heap_len.
439 #define pqremove(tree, top) \
441 top = heap[SMALLEST]; \
442 heap[SMALLEST] = heap[heap_len--]; \
443 pqdownheap(tree, SMALLEST); \
446 /* ===========================================================================
447 * Compares to subtrees, using the tree depth as tie breaker when
448 * the subtrees have equal frequency. This minimizes the worst case length.
450 #define smaller(tree, n, m) \
451 (tree[n].Freq < tree[m].Freq || \
452 (tree[n].Freq == tree[m].Freq && depth[n] <= depth[m]))
454 /* ===========================================================================
455 * Restore the heap property by moving down the tree starting at node k,
456 * exchanging a node with the smallest of its two sons if necessary, stopping
457 * when the heap property is re-established (each father smaller than its
458 * two sons).
460 local void pqdownheap(tree, k)
461 ct_data near *tree; /* the tree to restore */
462 int k; /* node to move down */
464 int v = heap[k];
465 int j = k << 1; /* left son of k */
466 while (j <= heap_len) {
467 /* Set j to the smallest of the two sons: */
468 if (j < heap_len && smaller(tree, heap[j+1], heap[j])) j++;
470 /* Exit if v is smaller than both sons */
471 if (smaller(tree, v, heap[j])) break;
473 /* Exchange v with the smallest son */
474 heap[k] = heap[j]; k = j;
476 /* And continue down the tree, setting j to the left son of k */
477 j <<= 1;
479 heap[k] = v;
482 /* ===========================================================================
483 * Compute the optimal bit lengths for a tree and update the total bit length
484 * for the current block.
485 * IN assertion: the fields freq and dad are set, heap[heap_max] and
486 * above are the tree nodes sorted by increasing frequency.
487 * OUT assertions: the field len is set to the optimal bit length, the
488 * array bl_count contains the frequencies for each bit length.
489 * The length opt_len is updated; static_len is also updated if stree is
490 * not null.
492 local void gen_bitlen(desc)
493 tree_desc near *desc; /* the tree descriptor */
495 ct_data near *tree = desc->dyn_tree;
496 int near *extra = desc->extra_bits;
497 int base = desc->extra_base;
498 int max_code = desc->max_code;
499 int max_length = desc->max_length;
500 ct_data near *stree = desc->static_tree;
501 int h; /* heap index */
502 int n, m; /* iterate over the tree elements */
503 int bits; /* bit length */
504 int xbits; /* extra bits */
505 ush f; /* frequency */
506 int overflow = 0; /* number of elements with bit length too large */
508 for (bits = 0; bits <= MAX_BITS; bits++) bl_count[bits] = 0;
510 /* In a first pass, compute the optimal bit lengths (which may
511 * overflow in the case of the bit length tree).
513 tree[heap[heap_max]].Len = 0; /* root of the heap */
515 for (h = heap_max+1; h < HEAP_SIZE; h++) {
516 n = heap[h];
517 bits = tree[tree[n].Dad].Len + 1;
518 if (bits > max_length) bits = max_length, overflow++;
519 tree[n].Len = (ush)bits;
520 /* We overwrite tree[n].Dad which is no longer needed */
522 if (n > max_code) continue; /* not a leaf node */
524 bl_count[bits]++;
525 xbits = 0;
526 if (n >= base) xbits = extra[n-base];
527 f = tree[n].Freq;
528 opt_len += (ulg)f * (bits + xbits);
529 if (stree) static_len += (ulg)f * (stree[n].Len + xbits);
531 if (overflow == 0) return;
533 Trace((stderr,"\nbit length overflow\n"));
534 /* This happens for example on obj2 and pic of the Calgary corpus */
536 /* Find the first bit length which could increase: */
537 do {
538 bits = max_length-1;
539 while (bl_count[bits] == 0) bits--;
540 bl_count[bits]--; /* move one leaf down the tree */
541 bl_count[bits+1] += 2; /* move one overflow item as its brother */
542 bl_count[max_length]--;
543 /* The brother of the overflow item also moves one step up,
544 * but this does not affect bl_count[max_length]
546 overflow -= 2;
547 } while (overflow > 0);
549 /* Now recompute all bit lengths, scanning in increasing frequency.
550 * h is still equal to HEAP_SIZE. (It is simpler to reconstruct all
551 * lengths instead of fixing only the wrong ones. This idea is taken
552 * from 'ar' written by Haruhiko Okumura.)
554 for (bits = max_length; bits != 0; bits--) {
555 n = bl_count[bits];
556 while (n != 0) {
557 m = heap[--h];
558 if (m > max_code) continue;
559 if (tree[m].Len != (unsigned) bits) {
560 Trace((stderr,"code %d bits %d->%d\n", m, tree[m].Len, bits));
561 opt_len += ((long)bits-(long)tree[m].Len)*(long)tree[m].Freq;
562 tree[m].Len = (ush)bits;
564 n--;
569 /* ===========================================================================
570 * Generate the codes for a given tree and bit counts (which need not be
571 * optimal).
572 * IN assertion: the array bl_count contains the bit length statistics for
573 * the given tree and the field len is set for all tree elements.
574 * OUT assertion: the field code is set for all tree elements of non
575 * zero code length.
577 local void gen_codes (tree, max_code)
578 ct_data near *tree; /* the tree to decorate */
579 int max_code; /* largest code with non zero frequency */
581 ush next_code[MAX_BITS+1]; /* next code value for each bit length */
582 ush code = 0; /* running code value */
583 int bits; /* bit index */
584 int n; /* code index */
586 /* The distribution counts are first used to generate the code values
587 * without bit reversal.
589 for (bits = 1; bits <= MAX_BITS; bits++) {
590 next_code[bits] = code = (code + bl_count[bits-1]) << 1;
592 /* Check that the bit counts in bl_count are consistent. The last code
593 * must be all ones.
595 Assert (code + bl_count[MAX_BITS]-1 == (1<<MAX_BITS)-1,
596 "inconsistent bit counts");
597 Tracev((stderr,"\ngen_codes: max_code %d ", max_code));
599 for (n = 0; n <= max_code; n++) {
600 int len = tree[n].Len;
601 if (len == 0) continue;
602 /* Now reverse the bits */
603 tree[n].Code = bi_reverse(next_code[len]++, len);
605 Tracec(tree != static_ltree, (stderr,"\nn %3d %c l %2d c %4x (%x) ",
606 n, (isgraph(n) ? n : ' '), len, tree[n].Code, next_code[len]-1));
610 /* ===========================================================================
611 * Construct one Huffman tree and assigns the code bit strings and lengths.
612 * Update the total bit length for the current block.
613 * IN assertion: the field freq is set for all tree elements.
614 * OUT assertions: the fields len and code are set to the optimal bit length
615 * and corresponding code. The length opt_len is updated; static_len is
616 * also updated if stree is not null. The field max_code is set.
618 local void build_tree(desc)
619 tree_desc near *desc; /* the tree descriptor */
621 ct_data near *tree = desc->dyn_tree;
622 ct_data near *stree = desc->static_tree;
623 int elems = desc->elems;
624 int n, m; /* iterate over heap elements */
625 int max_code = -1; /* largest code with non zero frequency */
626 int node = elems; /* next internal node of the tree */
628 /* Construct the initial heap, with least frequent element in
629 * heap[SMALLEST]. The sons of heap[n] are heap[2*n] and heap[2*n+1].
630 * heap[0] is not used.
632 heap_len = 0, heap_max = HEAP_SIZE;
634 for (n = 0; n < elems; n++) {
635 if (tree[n].Freq != 0) {
636 heap[++heap_len] = max_code = n;
637 depth[n] = 0;
638 } else {
639 tree[n].Len = 0;
643 /* The pkzip format requires that at least one distance code exists,
644 * and that at least one bit should be sent even if there is only one
645 * possible code. So to avoid special checks later on we force at least
646 * two codes of non zero frequency.
648 while (heap_len < 2) {
649 int new = heap[++heap_len] = (max_code < 2 ? ++max_code : 0);
650 tree[new].Freq = 1;
651 depth[new] = 0;
652 opt_len--; if (stree) static_len -= stree[new].Len;
653 /* new is 0 or 1 so it does not have extra bits */
655 desc->max_code = max_code;
657 /* The elements heap[heap_len/2+1 .. heap_len] are leaves of the tree,
658 * establish sub-heaps of increasing lengths:
660 for (n = heap_len/2; n >= 1; n--) pqdownheap(tree, n);
662 /* Construct the Huffman tree by repeatedly combining the least two
663 * frequent nodes.
665 do {
666 pqremove(tree, n); /* n = node of least frequency */
667 m = heap[SMALLEST]; /* m = node of next least frequency */
669 heap[--heap_max] = n; /* keep the nodes sorted by frequency */
670 heap[--heap_max] = m;
672 /* Create a new node father of n and m */
673 tree[node].Freq = tree[n].Freq + tree[m].Freq;
674 depth[node] = (uch) (MAX(depth[n], depth[m]) + 1);
675 tree[n].Dad = tree[m].Dad = (ush)node;
676 #ifdef DUMP_BL_TREE
677 if (tree == bl_tree) {
678 fprintf(stderr,"\nnode %d(%d), sons %d(%d) %d(%d)",
679 node, tree[node].Freq, n, tree[n].Freq, m, tree[m].Freq);
681 #endif
682 /* and insert the new node in the heap */
683 heap[SMALLEST] = node++;
684 pqdownheap(tree, SMALLEST);
686 } while (heap_len >= 2);
688 heap[--heap_max] = heap[SMALLEST];
690 /* At this point, the fields freq and dad are set. We can now
691 * generate the bit lengths.
693 gen_bitlen((tree_desc near *)desc);
695 /* The field len is now set, we can generate the bit codes */
696 gen_codes ((ct_data near *)tree, max_code);
699 /* ===========================================================================
700 * Scan a literal or distance tree to determine the frequencies of the codes
701 * in the bit length tree. Updates opt_len to take into account the repeat
702 * counts. (The contribution of the bit length codes will be added later
703 * during the construction of bl_tree.)
705 local void scan_tree (tree, max_code)
706 ct_data near *tree; /* the tree to be scanned */
707 int max_code; /* and its largest code of non zero frequency */
709 int n; /* iterates over all tree elements */
710 int prevlen = -1; /* last emitted length */
711 int curlen; /* length of current code */
712 int nextlen = tree[0].Len; /* length of next code */
713 int count = 0; /* repeat count of the current code */
714 int max_count = 7; /* max repeat count */
715 int min_count = 4; /* min repeat count */
717 if (nextlen == 0) max_count = 138, min_count = 3;
718 tree[max_code+1].Len = (ush)0xffff; /* guard */
720 for (n = 0; n <= max_code; n++) {
721 curlen = nextlen; nextlen = tree[n+1].Len;
722 if (++count < max_count && curlen == nextlen) {
723 continue;
724 } else if (count < min_count) {
725 bl_tree[curlen].Freq += count;
726 } else if (curlen != 0) {
727 if (curlen != prevlen) bl_tree[curlen].Freq++;
728 bl_tree[REP_3_6].Freq++;
729 } else if (count <= 10) {
730 bl_tree[REPZ_3_10].Freq++;
731 } else {
732 bl_tree[REPZ_11_138].Freq++;
734 count = 0; prevlen = curlen;
735 if (nextlen == 0) {
736 max_count = 138, min_count = 3;
737 } else if (curlen == nextlen) {
738 max_count = 6, min_count = 3;
739 } else {
740 max_count = 7, min_count = 4;
745 /* ===========================================================================
746 * Send a literal or distance tree in compressed form, using the codes in
747 * bl_tree.
749 local void send_tree (tree, max_code)
750 ct_data near *tree; /* the tree to be scanned */
751 int max_code; /* and its largest code of non zero frequency */
753 int n; /* iterates over all tree elements */
754 int prevlen = -1; /* last emitted length */
755 int curlen; /* length of current code */
756 int nextlen = tree[0].Len; /* length of next code */
757 int count = 0; /* repeat count of the current code */
758 int max_count = 7; /* max repeat count */
759 int min_count = 4; /* min repeat count */
761 /* tree[max_code+1].Len = -1; */ /* guard already set */
762 if (nextlen == 0) max_count = 138, min_count = 3;
764 for (n = 0; n <= max_code; n++) {
765 curlen = nextlen; nextlen = tree[n+1].Len;
766 if (++count < max_count && curlen == nextlen) {
767 continue;
768 } else if (count < min_count) {
769 do { send_code(curlen, bl_tree); } while (--count != 0);
771 } else if (curlen != 0) {
772 if (curlen != prevlen) {
773 send_code(curlen, bl_tree); count--;
775 Assert(count >= 3 && count <= 6, " 3_6?");
776 send_code(REP_3_6, bl_tree); send_bits(count-3, 2);
778 } else if (count <= 10) {
779 send_code(REPZ_3_10, bl_tree); send_bits(count-3, 3);
781 } else {
782 send_code(REPZ_11_138, bl_tree); send_bits(count-11, 7);
784 count = 0; prevlen = curlen;
785 if (nextlen == 0) {
786 max_count = 138, min_count = 3;
787 } else if (curlen == nextlen) {
788 max_count = 6, min_count = 3;
789 } else {
790 max_count = 7, min_count = 4;
795 /* ===========================================================================
796 * Construct the Huffman tree for the bit lengths and return the index in
797 * bl_order of the last bit length code to send.
799 local int build_bl_tree()
801 int max_blindex; /* index of last bit length code of non zero freq */
803 /* Determine the bit length frequencies for literal and distance trees */
804 scan_tree((ct_data near *)dyn_ltree, l_desc.max_code);
805 scan_tree((ct_data near *)dyn_dtree, d_desc.max_code);
807 /* Build the bit length tree: */
808 build_tree((tree_desc near *)(&bl_desc));
809 /* opt_len now includes the length of the tree representations, except
810 * the lengths of the bit lengths codes and the 5+5+4 bits for the counts.
813 /* Determine the number of bit length codes to send. The pkzip format
814 * requires that at least 4 bit length codes be sent. (appnote.txt says
815 * 3 but the actual value used is 4.)
817 for (max_blindex = BL_CODES-1; max_blindex >= 3; max_blindex--) {
818 if (bl_tree[bl_order[max_blindex]].Len != 0) break;
820 /* Update opt_len to include the bit length tree and counts */
821 opt_len += 3*(max_blindex+1) + 5+5+4;
822 Tracev((stderr, "\ndyn trees: dyn %lu, stat %lu", opt_len, static_len));
824 return max_blindex;
827 /* ===========================================================================
828 * Send the header for a block using dynamic Huffman trees: the counts, the
829 * lengths of the bit length codes, the literal tree and the distance tree.
830 * IN assertion: lcodes >= 257, dcodes >= 1, blcodes >= 4.
832 local void send_all_trees(lcodes, dcodes, blcodes)
833 int lcodes, dcodes, blcodes; /* number of codes for each tree */
835 int rank; /* index in bl_order */
837 Assert (lcodes >= 257 && dcodes >= 1 && blcodes >= 4, "not enough codes");
838 Assert (lcodes <= L_CODES && dcodes <= D_CODES && blcodes <= BL_CODES,
839 "too many codes");
840 Tracev((stderr, "\nbl counts: "));
841 send_bits(lcodes-257, 5); /* not +255 as stated in appnote.txt */
842 send_bits(dcodes-1, 5);
843 send_bits(blcodes-4, 4); /* not -3 as stated in appnote.txt */
844 for (rank = 0; rank < blcodes; rank++) {
845 Tracev((stderr, "\nbl code %2d ", bl_order[rank]));
846 send_bits(bl_tree[bl_order[rank]].Len, 3);
849 send_tree((ct_data near *)dyn_ltree, lcodes-1); /* send the literal tree */
851 send_tree((ct_data near *)dyn_dtree, dcodes-1); /* send the distance tree */
854 /* ===========================================================================
855 * Determine the best encoding for the current block: dynamic trees, static
856 * trees or store, and output the encoded block to the zip file. This function
857 * returns the total compressed length for the file so far.
859 off_t flush_block(buf, stored_len, eof)
860 char *buf; /* input block, or NULL if too old */
861 ulg stored_len; /* length of input block */
862 int eof; /* true if this is the last block for a file */
864 ulg opt_lenb, static_lenb; /* opt_len and static_len in bytes */
865 int max_blindex; /* index of last bit length code of non zero freq */
867 flag_buf[last_flags] = flags; /* Save the flags for the last 8 items */
869 /* Check if the file is ascii or binary */
870 if (*file_type == (ush)UNKNOWN) set_file_type();
872 /* Construct the literal and distance trees */
873 build_tree((tree_desc near *)(&l_desc));
874 Tracev((stderr, "\nlit data: dyn %lu, stat %lu", opt_len, static_len));
876 build_tree((tree_desc near *)(&d_desc));
877 Tracev((stderr, "\ndist data: dyn %lu, stat %lu", opt_len, static_len));
878 /* At this point, opt_len and static_len are the total bit lengths of
879 * the compressed block data, excluding the tree representations.
882 /* Build the bit length tree for the above two trees, and get the index
883 * in bl_order of the last bit length code to send.
885 max_blindex = build_bl_tree();
887 /* Determine the best encoding. Compute first the block length in bytes */
888 opt_lenb = (opt_len+3+7)>>3;
889 static_lenb = (static_len+3+7)>>3;
890 input_len += stored_len; /* for debugging only */
892 Trace((stderr, "\nopt %lu(%lu) stat %lu(%lu) stored %lu lit %u dist %u ",
893 opt_lenb, opt_len, static_lenb, static_len, stored_len,
894 last_lit, last_dist));
896 if (static_lenb <= opt_lenb) opt_lenb = static_lenb;
898 /* If compression failed and this is the first and last block,
899 * and if the zip file can be seeked (to rewrite the local header),
900 * the whole file is transformed into a stored file:
902 #ifdef FORCE_METHOD
903 if (level == 1 && eof && compressed_len == 0L) { /* force stored file */
904 #else
905 if (stored_len <= opt_lenb && eof && compressed_len == 0L && seekable()) {
906 #endif
907 /* Since LIT_BUFSIZE <= 2*WSIZE, the input data must be there: */
908 if (!buf)
909 gzip_error ("block vanished");
911 copy_block(buf, (unsigned)stored_len, 0); /* without header */
912 compressed_len = stored_len << 3;
913 *file_method = STORED;
915 #ifdef FORCE_METHOD
916 } else if (level == 2 && buf != (char*)0) { /* force stored block */
917 #else
918 } else if (stored_len+4 <= opt_lenb && buf != (char*)0) {
919 /* 4: two words for the lengths */
920 #endif
921 /* The test buf != NULL is only necessary if LIT_BUFSIZE > WSIZE.
922 * Otherwise we can't have processed more than WSIZE input bytes since
923 * the last block flush, because compression would have been
924 * successful. If LIT_BUFSIZE <= WSIZE, it is never too late to
925 * transform a block into a stored block.
927 send_bits((STORED_BLOCK<<1)+eof, 3); /* send block type */
928 compressed_len = (compressed_len + 3 + 7) & ~7L;
929 compressed_len += (stored_len + 4) << 3;
931 copy_block(buf, (unsigned)stored_len, 1); /* with header */
933 #ifdef FORCE_METHOD
934 } else if (level == 3) { /* force static trees */
935 #else
936 } else if (static_lenb == opt_lenb) {
937 #endif
938 send_bits((STATIC_TREES<<1)+eof, 3);
939 compress_block((ct_data near *)static_ltree, (ct_data near *)static_dtree);
940 compressed_len += 3 + static_len;
941 } else {
942 send_bits((DYN_TREES<<1)+eof, 3);
943 send_all_trees(l_desc.max_code+1, d_desc.max_code+1, max_blindex+1);
944 compress_block((ct_data near *)dyn_ltree, (ct_data near *)dyn_dtree);
945 compressed_len += 3 + opt_len;
947 Assert (compressed_len == bits_sent, "bad compressed size");
948 init_block();
950 if (eof) {
951 Assert (input_len == bytes_in, "bad input size");
952 bi_windup();
953 compressed_len += 7; /* align on byte boundary */
956 return compressed_len >> 3;
959 /* ===========================================================================
960 * Save the match info and tally the frequency counts. Return true if
961 * the current block must be flushed.
963 int ct_tally (dist, lc)
964 int dist; /* distance of matched string */
965 int lc; /* match length-MIN_MATCH or unmatched char (if dist==0) */
967 l_buf[last_lit++] = (uch)lc;
968 if (dist == 0) {
969 /* lc is the unmatched char */
970 dyn_ltree[lc].Freq++;
971 } else {
972 /* Here, lc is the match length - MIN_MATCH */
973 dist--; /* dist = match distance - 1 */
974 Assert((ush)dist < (ush)MAX_DIST &&
975 (ush)lc <= (ush)(MAX_MATCH-MIN_MATCH) &&
976 (ush)d_code(dist) < (ush)D_CODES, "ct_tally: bad match");
978 dyn_ltree[length_code[lc]+LITERALS+1].Freq++;
979 dyn_dtree[d_code(dist)].Freq++;
981 d_buf[last_dist++] = (ush)dist;
982 flags |= flag_bit;
984 flag_bit <<= 1;
986 /* Output the flags if they fill a byte: */
987 if ((last_lit & 7) == 0) {
988 flag_buf[last_flags++] = flags;
989 flags = 0, flag_bit = 1;
991 /* Try to guess if it is profitable to stop the current block here */
992 if (level > 2 && (last_lit & 0xfff) == 0) {
993 /* Compute an upper bound for the compressed length */
994 ulg out_length = (ulg)last_lit*8L;
995 ulg in_length = (ulg)strstart-block_start;
996 int dcode;
997 for (dcode = 0; dcode < D_CODES; dcode++) {
998 out_length += (ulg)dyn_dtree[dcode].Freq*(5L+extra_dbits[dcode]);
1000 out_length >>= 3;
1001 Trace((stderr,"\nlast_lit %u, last_dist %u, in %ld, out ~%ld(%ld%%) ",
1002 last_lit, last_dist, in_length, out_length,
1003 100L - out_length*100L/in_length));
1004 if (last_dist < last_lit/2 && out_length < in_length/2) return 1;
1006 return (last_lit == LIT_BUFSIZE-1 || last_dist == DIST_BUFSIZE);
1007 /* We avoid equality with LIT_BUFSIZE because of wraparound at 64K
1008 * on 16 bit machines and because stored blocks are restricted to
1009 * 64K-1 bytes.
1013 /* ===========================================================================
1014 * Send the block data compressed using the given Huffman trees
1016 local void compress_block(ltree, dtree)
1017 ct_data near *ltree; /* literal tree */
1018 ct_data near *dtree; /* distance tree */
1020 unsigned dist; /* distance of matched string */
1021 int lc; /* match length or unmatched char (if dist == 0) */
1022 unsigned lx = 0; /* running index in l_buf */
1023 unsigned dx = 0; /* running index in d_buf */
1024 unsigned fx = 0; /* running index in flag_buf */
1025 uch flag = 0; /* current flags */
1026 unsigned code; /* the code to send */
1027 int extra; /* number of extra bits to send */
1029 if (last_lit != 0) do {
1030 if ((lx & 7) == 0) flag = flag_buf[fx++];
1031 lc = l_buf[lx++];
1032 if ((flag & 1) == 0) {
1033 send_code(lc, ltree); /* send a literal byte */
1034 Tracecv(isgraph(lc), (stderr," '%c' ", lc));
1035 } else {
1036 /* Here, lc is the match length - MIN_MATCH */
1037 code = length_code[lc];
1038 send_code(code+LITERALS+1, ltree); /* send the length code */
1039 extra = extra_lbits[code];
1040 if (extra != 0) {
1041 lc -= base_length[code];
1042 send_bits(lc, extra); /* send the extra length bits */
1044 dist = d_buf[dx++];
1045 /* Here, dist is the match distance - 1 */
1046 code = d_code(dist);
1047 Assert (code < D_CODES, "bad d_code");
1049 send_code(code, dtree); /* send the distance code */
1050 extra = extra_dbits[code];
1051 if (extra != 0) {
1052 dist -= base_dist[code];
1053 send_bits(dist, extra); /* send the extra distance bits */
1055 } /* literal or match pair ? */
1056 flag >>= 1;
1057 } while (lx < last_lit);
1059 send_code(END_BLOCK, ltree);
1062 /* ===========================================================================
1063 * Set the file type to ASCII or BINARY, using a crude approximation:
1064 * binary if more than 20% of the bytes are <= 6 or >= 128, ascii otherwise.
1065 * IN assertion: the fields freq of dyn_ltree are set and the total of all
1066 * frequencies does not exceed 64K (to fit in an int on 16 bit machines).
1068 local void set_file_type()
1070 int n = 0;
1071 unsigned ascii_freq = 0;
1072 unsigned bin_freq = 0;
1073 while (n < 7) bin_freq += dyn_ltree[n++].Freq;
1074 while (n < 128) ascii_freq += dyn_ltree[n++].Freq;
1075 while (n < LITERALS) bin_freq += dyn_ltree[n++].Freq;
1076 *file_type = bin_freq > (ascii_freq >> 2) ? BINARY : ASCII;
1077 if (*file_type == BINARY && translate_eol) {
1078 warning ("-l used on binary file");