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bcf78a2 @madler zlib 0.71
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1 /* deflate.h -- internal compression state
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2 * Copyright (C) 1995-2002 Jean-loup Gailly
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3 * For conditions of distribution and use, see copyright notice in zlib.h
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4 */
5
6 /* WARNING: this file should *not* be used by applications. It is
7 part of the implementation of the compression library and is
8 subject to change. Applications should only use zlib.h.
9 */
10
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11 /* @(#) $Id$ */
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12
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13 #ifndef DEFLATE_H
14 #define DEFLATE_H
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15
16 #include "zutil.h"
17
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18 /* define NO_GZIP when compiling if you want to disable gzip header and
19 trailer creation by deflate(). NO_GZIP would be used to avoid linking in
20 the crc code when it is not needed. For shared libraries, gzip encoding
21 should be left enabled. */
22 #ifndef NO_GZIP
23 # define GZIP
24 #endif
25
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26 /* ===========================================================================
27 * Internal compression state.
28 */
29
30 #define LENGTH_CODES 29
31 /* number of length codes, not counting the special END_BLOCK code */
32
33 #define LITERALS 256
34 /* number of literal bytes 0..255 */
35
36 #define L_CODES (LITERALS+1+LENGTH_CODES)
37 /* number of Literal or Length codes, including the END_BLOCK code */
38
39 #define D_CODES 30
40 /* number of distance codes */
41
42 #define BL_CODES 19
43 /* number of codes used to transfer the bit lengths */
44
45 #define HEAP_SIZE (2*L_CODES+1)
46 /* maximum heap size */
47
48 #define MAX_BITS 15
49 /* All codes must not exceed MAX_BITS bits */
50
51 #define INIT_STATE 42
52 #define BUSY_STATE 113
53 #define FINISH_STATE 666
54 /* Stream status */
55
56
57 /* Data structure describing a single value and its code string. */
58 typedef struct ct_data_s {
59 union {
60 ush freq; /* frequency count */
61 ush code; /* bit string */
62 } fc;
63 union {
64 ush dad; /* father node in Huffman tree */
65 ush len; /* length of bit string */
66 } dl;
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67 } FAR ct_data;
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68
69 #define Freq fc.freq
70 #define Code fc.code
71 #define Dad dl.dad
72 #define Len dl.len
73
74 typedef struct static_tree_desc_s static_tree_desc;
75
76 typedef struct tree_desc_s {
77 ct_data *dyn_tree; /* the dynamic tree */
78 int max_code; /* largest code with non zero frequency */
79 static_tree_desc *stat_desc; /* the corresponding static tree */
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80 } FAR tree_desc;
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81
82 typedef ush Pos;
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83 typedef Pos FAR Posf;
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84 typedef unsigned IPos;
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85
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86 /* A Pos is an index in the character window. We use short instead of int to
87 * save space in the various tables. IPos is used only for parameter passing.
88 */
89
90 typedef struct internal_state {
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91 z_streamp strm; /* pointer back to this zlib stream */
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92 int status; /* as the name implies */
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93 Bytef *pending_buf; /* output still pending */
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94 ulg pending_buf_size; /* size of pending_buf */
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95 Bytef *pending_out; /* next pending byte to output to the stream */
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96 int pending; /* nb of bytes in the pending buffer */
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97 int wrap; /* bit 0 true for zlib, bit 1 true for gzip */
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98 Byte data_type; /* UNKNOWN, BINARY or ASCII */
99 Byte method; /* STORED (for zip only) or DEFLATED */
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100 int last_flush; /* value of flush param for previous deflate call */
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101
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102 /* used by deflate.c: */
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103
104 uInt w_size; /* LZ77 window size (32K by default) */
105 uInt w_bits; /* log2(w_size) (8..16) */
106 uInt w_mask; /* w_size - 1 */
107
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108 Bytef *window;
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109 /* Sliding window. Input bytes are read into the second half of the window,
110 * and move to the first half later to keep a dictionary of at least wSize
111 * bytes. With this organization, matches are limited to a distance of
112 * wSize-MAX_MATCH bytes, but this ensures that IO is always
113 * performed with a length multiple of the block size. Also, it limits
114 * the window size to 64K, which is quite useful on MSDOS.
115 * To do: use the user input buffer as sliding window.
116 */
117
118 ulg window_size;
119 /* Actual size of window: 2*wSize, except when the user input buffer
120 * is directly used as sliding window.
121 */
122
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123 Posf *prev;
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124 /* Link to older string with same hash index. To limit the size of this
125 * array to 64K, this link is maintained only for the last 32K strings.
126 * An index in this array is thus a window index modulo 32K.
127 */
128
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129 Posf *head; /* Heads of the hash chains or NIL. */
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130
131 uInt ins_h; /* hash index of string to be inserted */
132 uInt hash_size; /* number of elements in hash table */
133 uInt hash_bits; /* log2(hash_size) */
134 uInt hash_mask; /* hash_size-1 */
135
136 uInt hash_shift;
137 /* Number of bits by which ins_h must be shifted at each input
138 * step. It must be such that after MIN_MATCH steps, the oldest
139 * byte no longer takes part in the hash key, that is:
140 * hash_shift * MIN_MATCH >= hash_bits
141 */
142
143 long block_start;
144 /* Window position at the beginning of the current output block. Gets
145 * negative when the window is moved backwards.
146 */
147
148 uInt match_length; /* length of best match */
149 IPos prev_match; /* previous match */
150 int match_available; /* set if previous match exists */
151 uInt strstart; /* start of string to insert */
152 uInt match_start; /* start of matching string */
153 uInt lookahead; /* number of valid bytes ahead in window */
154
155 uInt prev_length;
156 /* Length of the best match at previous step. Matches not greater than this
157 * are discarded. This is used in the lazy match evaluation.
158 */
159
160 uInt max_chain_length;
161 /* To speed up deflation, hash chains are never searched beyond this
162 * length. A higher limit improves compression ratio but degrades the
163 * speed.
164 */
165
166 uInt max_lazy_match;
167 /* Attempt to find a better match only when the current match is strictly
168 * smaller than this value. This mechanism is used only for compression
169 * levels >= 4.
170 */
171 # define max_insert_length max_lazy_match
172 /* Insert new strings in the hash table only if the match length is not
173 * greater than this length. This saves time but degrades compression.
174 * max_insert_length is used only for compression levels <= 3.
175 */
176
177 int level; /* compression level (1..9) */
178 int strategy; /* favor or force Huffman coding*/
179
180 uInt good_match;
181 /* Use a faster search when the previous match is longer than this */
182
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183 int nice_match; /* Stop searching when current match exceeds this */
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184
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185 /* used by trees.c: */
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186 /* Didn't use ct_data typedef below to supress compiler warning */
187 struct ct_data_s dyn_ltree[HEAP_SIZE]; /* literal and length tree */
188 struct ct_data_s dyn_dtree[2*D_CODES+1]; /* distance tree */
189 struct ct_data_s bl_tree[2*BL_CODES+1]; /* Huffman tree for bit lengths */
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190
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191 struct tree_desc_s l_desc; /* desc. for literal tree */
192 struct tree_desc_s d_desc; /* desc. for distance tree */
193 struct tree_desc_s bl_desc; /* desc. for bit length tree */
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194
195 ush bl_count[MAX_BITS+1];
196 /* number of codes at each bit length for an optimal tree */
197
198 int heap[2*L_CODES+1]; /* heap used to build the Huffman trees */
199 int heap_len; /* number of elements in the heap */
200 int heap_max; /* element of largest frequency */
201 /* The sons of heap[n] are heap[2*n] and heap[2*n+1]. heap[0] is not used.
202 * The same heap array is used to build all trees.
203 */
204
205 uch depth[2*L_CODES+1];
206 /* Depth of each subtree used as tie breaker for trees of equal frequency
207 */
208
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209 uchf *l_buf; /* buffer for literals or lengths */
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210
211 uInt lit_bufsize;
212 /* Size of match buffer for literals/lengths. There are 4 reasons for
213 * limiting lit_bufsize to 64K:
214 * - frequencies can be kept in 16 bit counters
215 * - if compression is not successful for the first block, all input
216 * data is still in the window so we can still emit a stored block even
217 * when input comes from standard input. (This can also be done for
218 * all blocks if lit_bufsize is not greater than 32K.)
219 * - if compression is not successful for a file smaller than 64K, we can
220 * even emit a stored file instead of a stored block (saving 5 bytes).
221 * This is applicable only for zip (not gzip or zlib).
222 * - creating new Huffman trees less frequently may not provide fast
223 * adaptation to changes in the input data statistics. (Take for
224 * example a binary file with poorly compressible code followed by
225 * a highly compressible string table.) Smaller buffer sizes give
226 * fast adaptation but have of course the overhead of transmitting
227 * trees more frequently.
228 * - I can't count above 4
229 */
230
231 uInt last_lit; /* running index in l_buf */
232
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233 ushf *d_buf;
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234 /* Buffer for distances. To simplify the code, d_buf and l_buf have
235 * the same number of elements. To use different lengths, an extra flag
236 * array would be necessary.
237 */
238
239 ulg opt_len; /* bit length of current block with optimal trees */
240 ulg static_len; /* bit length of current block with static trees */
241 uInt matches; /* number of string matches in current block */
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242 int last_eob_len; /* bit length of EOB code for last block */
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243
244 #ifdef DEBUG
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245 ulg compressed_len; /* total bit length of compressed file mod 2^32 */
246 ulg bits_sent; /* bit length of compressed data sent mod 2^32 */
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247 #endif
248
249 ush bi_buf;
250 /* Output buffer. bits are inserted starting at the bottom (least
251 * significant bits).
252 */
253 int bi_valid;
254 /* Number of valid bits in bi_buf. All bits above the last valid bit
255 * are always zero.
256 */
257
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258 } FAR deflate_state;
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259
260 /* Output a byte on the stream.
261 * IN assertion: there is enough room in pending_buf.
262 */
263 #define put_byte(s, c) {s->pending_buf[s->pending++] = (c);}
264
265
266 #define MIN_LOOKAHEAD (MAX_MATCH+MIN_MATCH+1)
267 /* Minimum amount of lookahead, except at the end of the input file.
268 * See deflate.c for comments about the MIN_MATCH+1.
269 */
270
271 #define MAX_DIST(s) ((s)->w_size-MIN_LOOKAHEAD)
272 /* In order to simplify the code, particularly on 16 bit machines, match
273 * distances are limited to MAX_DIST instead of WSIZE.
274 */
275
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276 /* in trees.c */
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277 void _tr_init OF((deflate_state *s));
278 int _tr_tally OF((deflate_state *s, unsigned dist, unsigned lc));
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279 void _tr_flush_block OF((deflate_state *s, charf *buf, ulg stored_len,
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280 int eof));
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281 void _tr_align OF((deflate_state *s));
282 void _tr_stored_block OF((deflate_state *s, charf *buf, ulg stored_len,
283 int eof));
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284
285 #define d_code(dist) \
286 ((dist) < 256 ? _dist_code[dist] : _dist_code[256+((dist)>>7)])
287 /* Mapping from a distance to a distance code. dist is the distance - 1 and
288 * must not have side effects. _dist_code[256] and _dist_code[257] are never
289 * used.
290 */
291
292 #ifndef DEBUG
293 /* Inline versions of _tr_tally for speed: */
294
295 #if defined(GEN_TREES_H) || !defined(STDC)
296 extern uch _length_code[];
297 extern uch _dist_code[];
298 #else
299 extern const uch _length_code[];
300 extern const uch _dist_code[];
301 #endif
302
303 # define _tr_tally_lit(s, c, flush) \
304 { uch cc = (c); \
305 s->d_buf[s->last_lit] = 0; \
306 s->l_buf[s->last_lit++] = cc; \
307 s->dyn_ltree[cc].Freq++; \
308 flush = (s->last_lit == s->lit_bufsize-1); \
309 }
310 # define _tr_tally_dist(s, distance, length, flush) \
311 { uch len = (length); \
312 ush dist = (distance); \
313 s->d_buf[s->last_lit] = dist; \
314 s->l_buf[s->last_lit++] = len; \
315 dist--; \
316 s->dyn_ltree[_length_code[len]+LITERALS+1].Freq++; \
317 s->dyn_dtree[d_code(dist)].Freq++; \
318 flush = (s->last_lit == s->lit_bufsize-1); \
319 }
320 #else
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321 # define _tr_tally_lit(s, c, flush) flush = _tr_tally(s, 0, c)
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322 # define _tr_tally_dist(s, distance, length, flush) \
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323 flush = _tr_tally(s, distance, length)
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324 #endif
325
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326 #endif /* DEFLATE_H */
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