1 /* deflate.h -- internal compression state
2 * Copyright (C) 1995-1998 Jean-loup Gailly
3 * For conditions of distribution and use, see copyright notice in zlib.h
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.
18 /* ===========================================================================
19 * Internal compression state.
22 #define LENGTH_CODES 29
23 /* number of length codes, not counting the special END_BLOCK code */
26 /* number of literal bytes 0..255 */
28 #define L_CODES (LITERALS+1+LENGTH_CODES)
29 /* number of Literal or Length codes, including the END_BLOCK code */
32 /* number of distance codes */
35 /* number of codes used to transfer the bit lengths */
37 #define HEAP_SIZE (2*L_CODES+1)
38 /* maximum heap size */
41 /* All codes must not exceed MAX_BITS bits */
44 #define BUSY_STATE 113
45 #define FINISH_STATE 666
49 /* Data structure describing a single value and its code string. */
50 typedef struct ct_data_s {
52 ush freq; /* frequency count */
53 ush code; /* bit string */
56 ush dad; /* father node in Huffman tree */
57 ush len; /* length of bit string */
66 typedef struct static_tree_desc_s static_tree_desc;
68 typedef struct tree_desc_s {
69 ct_data *dyn_tree; /* the dynamic tree */
70 int max_code; /* largest code with non zero frequency */
71 const static_tree_desc *stat_desc; /* the corresponding static tree */
76 typedef unsigned IPos;
78 /* A Pos is an index in the character window. We use short instead of int to
79 * save space in the various tables. IPos is used only for parameter passing.
82 typedef struct internal_state {
83 z_streamp strm; /* pointer back to this zlib stream */
84 int status; /* as the name implies */
85 Bytef *pending_buf; /* output still pending */
86 ulg pending_buf_size; /* size of pending_buf */
87 Bytef *pending_out; /* next pending byte to output to the stream */
88 int pending; /* nb of bytes in the pending buffer */
89 int noheader; /* suppress zlib header and adler32 */
90 Byte data_type; /* UNKNOWN, BINARY or ASCII */
91 Byte method; /* STORED (for zip only) or DEFLATED */
92 int last_flush; /* value of flush param for previous deflate call */
94 /* used by deflate.c: */
96 uInt w_size; /* LZ77 window size (32K by default) */
97 uInt w_bits; /* log2(w_size) (8..16) */
98 uInt w_mask; /* w_size - 1 */
101 /* Sliding window. Input bytes are read into the second half of the window,
102 * and move to the first half later to keep a dictionary of at least wSize
103 * bytes. With this organization, matches are limited to a distance of
104 * wSize-MAX_MATCH bytes, but this ensures that IO is always
105 * performed with a length multiple of the block size. Also, it limits
106 * the window size to 64K, which is quite useful on MSDOS.
107 * To do: use the user input buffer as sliding window.
111 /* Actual size of window: 2*wSize, except when the user input buffer
112 * is directly used as sliding window.
116 /* Link to older string with same hash index. To limit the size of this
117 * array to 64K, this link is maintained only for the last 32K strings.
118 * An index in this array is thus a window index modulo 32K.
121 Posf *head; /* Heads of the hash chains or NIL. */
123 uInt ins_h; /* hash index of string to be inserted */
124 uInt hash_size; /* number of elements in hash table */
125 uInt hash_bits; /* log2(hash_size) */
126 uInt hash_mask; /* hash_size-1 */
129 /* Number of bits by which ins_h must be shifted at each input
130 * step. It must be such that after MIN_MATCH steps, the oldest
131 * byte no longer takes part in the hash key, that is:
132 * hash_shift * MIN_MATCH >= hash_bits
136 /* Window position at the beginning of the current output block. Gets
137 * negative when the window is moved backwards.
140 uInt match_length; /* length of best match */
141 IPos prev_match; /* previous match */
142 int match_available; /* set if previous match exists */
143 uInt strstart; /* start of string to insert */
144 uInt match_start; /* start of matching string */
145 uInt lookahead; /* number of valid bytes ahead in window */
148 /* Length of the best match at previous step. Matches not greater than this
149 * are discarded. This is used in the lazy match evaluation.
152 uInt max_chain_length;
153 /* To speed up deflation, hash chains are never searched beyond this
154 * length. A higher limit improves compression ratio but degrades the
159 /* Attempt to find a better match only when the current match is strictly
160 * smaller than this value. This mechanism is used only for compression
163 # define max_insert_length max_lazy_match
164 /* Insert new strings in the hash table only if the match length is not
165 * greater than this length. This saves time but degrades compression.
166 * max_insert_length is used only for compression levels <= 3.
169 int level; /* compression level (1..9) */
170 int strategy; /* favor or force Huffman coding*/
173 /* Use a faster search when the previous match is longer than this */
175 int nice_match; /* Stop searching when current match exceeds this */
177 /* used by trees.c: */
178 /* Didn't use ct_data typedef below to supress compiler warning */
179 struct ct_data_s dyn_ltree[HEAP_SIZE]; /* literal and length tree */
180 struct ct_data_s dyn_dtree[2*D_CODES+1]; /* distance tree */
181 struct ct_data_s bl_tree[2*BL_CODES+1]; /* Huffman tree for bit lengths */
183 struct tree_desc_s l_desc; /* desc. for literal tree */
184 struct tree_desc_s d_desc; /* desc. for distance tree */
185 struct tree_desc_s bl_desc; /* desc. for bit length tree */
187 ush bl_count[MAX_BITS+1];
188 /* number of codes at each bit length for an optimal tree */
190 int heap[2*L_CODES+1]; /* heap used to build the Huffman trees */
191 int heap_len; /* number of elements in the heap */
192 int heap_max; /* element of largest frequency */
193 /* The sons of heap[n] are heap[2*n] and heap[2*n+1]. heap[0] is not used.
194 * The same heap array is used to build all trees.
197 uch depth[2*L_CODES+1];
198 /* Depth of each subtree used as tie breaker for trees of equal frequency
201 uchf *l_buf; /* buffer for literals or lengths */
204 /* Size of match buffer for literals/lengths. There are 4 reasons for
205 * limiting lit_bufsize to 64K:
206 * - frequencies can be kept in 16 bit counters
207 * - if compression is not successful for the first block, all input
208 * data is still in the window so we can still emit a stored block even
209 * when input comes from standard input. (This can also be done for
210 * all blocks if lit_bufsize is not greater than 32K.)
211 * - if compression is not successful for a file smaller than 64K, we can
212 * even emit a stored file instead of a stored block (saving 5 bytes).
213 * This is applicable only for zip (not gzip or zlib).
214 * - creating new Huffman trees less frequently may not provide fast
215 * adaptation to changes in the input data statistics. (Take for
216 * example a binary file with poorly compressible code followed by
217 * a highly compressible string table.) Smaller buffer sizes give
218 * fast adaptation but have of course the overhead of transmitting
219 * trees more frequently.
220 * - I can't count above 4
223 uInt last_lit; /* running index in l_buf */
226 /* Buffer for distances. To simplify the code, d_buf and l_buf have
227 * the same number of elements. To use different lengths, an extra flag
228 * array would be necessary.
231 ulg opt_len; /* bit length of current block with optimal trees */
232 ulg static_len; /* bit length of current block with static trees */
233 uInt matches; /* number of string matches in current block */
234 int last_eob_len; /* bit length of EOB code for last block */
237 ulg compressed_len; /* total bit length of compressed file mod 2^32 */
238 ulg bits_sent; /* bit length of compressed data sent mod 2^32 */
242 /* Output buffer. bits are inserted starting at the bottom (least
246 /* Number of valid bits in bi_buf. All bits above the last valid bit
252 /* Output a byte on the stream.
253 * IN assertion: there is enough room in pending_buf.
255 #define put_byte(s, c) {s->pending_buf[s->pending++] = (c);}
258 #define MIN_LOOKAHEAD (MAX_MATCH+MIN_MATCH+1)
259 /* Minimum amount of lookahead, except at the end of the input file.
260 * See deflate.c for comments about the MIN_MATCH+1.
263 #define MAX_DIST(s) ((s)->w_size-MIN_LOOKAHEAD)
264 /* In order to simplify the code, particularly on 16 bit machines, match
265 * distances are limited to MAX_DIST instead of WSIZE.
269 void _tr_init OF((deflate_state *s));
270 int _tr_tally OF((deflate_state *s, unsigned dist, unsigned lc));
271 void _tr_flush_block OF((deflate_state *s, charf *buf, ulg stored_len,
273 void _tr_align OF((deflate_state *s));
274 void _tr_stored_block OF((deflate_state *s, charf *buf, ulg stored_len,
277 #define d_code(dist) \
278 ((dist) < 256 ? _dist_code[dist] : _dist_code[256+((dist)>>7)])
279 /* Mapping from a distance to a distance code. dist is the distance - 1 and
280 * must not have side effects. _dist_code[256] and _dist_code[257] are never
285 /* Inline versions of _tr_tally for speed: */
287 #if defined(GEN_TREES_H) || !defined(STDC)
288 extern uch _length_code[];
289 extern uch _dist_code[];
291 extern const uch _length_code[];
292 extern const uch _dist_code[];
295 # define _tr_tally_lit(s, c, flush) \
297 s->d_buf[s->last_lit] = 0; \
298 s->l_buf[s->last_lit++] = cc; \
299 s->dyn_ltree[cc].Freq++; \
300 flush = (s->last_lit == s->lit_bufsize-1); \
302 # define _tr_tally_dist(s, distance, length, flush) \
303 { uch len = STATIC_CAST(uch,length); \
304 ush dist = STATIC_CAST(ush,distance); \
305 s->d_buf[s->last_lit] = dist; \
306 s->l_buf[s->last_lit++] = len; \
308 s->dyn_ltree[_length_code[len]+LITERALS+1].Freq++; \
309 s->dyn_dtree[d_code(dist)].Freq++; \
310 flush = (s->last_lit == s->lit_bufsize-1); \
313 # define _tr_tally_lit(s, c, flush) flush = _tr_tally(s, 0, c)
314 # define _tr_tally_dist(s, distance, length, flush) \
315 flush = _tr_tally(s, distance, length)