zlib/deflate.h

   1 /* deflate.h -- internal compression state
   2  * Copyright (C) 1995-2012 Jean-loup Gailly
   3  * For conditions of distribution and use, see copyright notice in zlib.h
   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
  11 /* @(#) $Id: deflate.h,v 1.1.1.2 2002/03/11 21:53:23 tromey Exp $ */
  12
  13 #ifndef DEFLATE_H
  14 #define DEFLATE_H
  15
  16 #include "zutil.h"
  17
  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
  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 Buf_size 16
  52 /* size of bit buffer in bi_buf */
  53
  54 #define INIT_STATE    42
  55 #define EXTRA_STATE   69
  56 #define NAME_STATE    73
  57 #define COMMENT_STATE 91
  58 #define HCRC_STATE   103
  59 #define BUSY_STATE   113
  60 #define FINISH_STATE 666
  61 /* Stream status */
  62
  63
  64 /* Data structure describing a single value and its code string. */
  65 typedef struct ct_data_s {
  66     union {
  67         ush  freq;       /* frequency count */
  68         ush  code;       /* bit string */
  69     } fc;
  70     union {
  71         ush  dad;        /* father node in Huffman tree */
  72         ush  len;        /* length of bit string */
  73     } dl;
  74 } FAR ct_data;
  75
  76 #define Freq fc.freq
  77 #define Code fc.code
  78 #define Dad  dl.dad
  79 #define Len  dl.len
  80
  81 typedef struct static_tree_desc_s  static_tree_desc;
  82
  83 typedef struct tree_desc_s {
  84     ct_data *dyn_tree;           /* the dynamic tree */
  85     int     max_code;            /* largest code with non zero frequency */
  86     static_tree_desc *stat_desc; /* the corresponding static tree */
  87 } FAR tree_desc;
  88
  89 typedef ush Pos;
  90 typedef Pos FAR Posf;
  91 typedef unsigned IPos;
  92
  93 /* A Pos is an index in the character window. We use short instead of int to
  94  * save space in the various tables. IPos is used only for parameter passing.
  95  */
  96
  97 typedef struct internal_state {
  98     z_streamp strm;      /* pointer back to this zlib stream */
  99     int   status;        /* as the name implies */
 100     Bytef *pending_buf;  /* output still pending */
 101     ulg   pending_buf_size; /* size of pending_buf */
 102     Bytef *pending_out;  /* next pending byte to output to the stream */
 103     uInt   pending;      /* nb of bytes in the pending buffer */
 104     int   wrap;          /* bit 0 true for zlib, bit 1 true for gzip */
 105     gz_headerp  gzhead;  /* gzip header information to write */
 106     uInt   gzindex;      /* where in extra, name, or comment */
 107     Byte  method;        /* STORED (for zip only) or DEFLATED */
 108     int   last_flush;    /* value of flush param for previous deflate call */
 109
 110                 /* used by deflate.c: */
 111
 112     uInt  w_size;        /* LZ77 window size (32K by default) */
 113     uInt  w_bits;        /* log2(w_size)  (8..16) */
 114     uInt  w_mask;        /* w_size - 1 */
 115
 116     Bytef *window;
 117     /* Sliding window. Input bytes are read into the second half of the window,
 118      * and move to the first half later to keep a dictionary of at least wSize
 119      * bytes. With this organization, matches are limited to a distance of
 120      * wSize-MAX_MATCH bytes, but this ensures that IO is always
 121      * performed with a length multiple of the block size. Also, it limits
 122      * the window size to 64K, which is quite useful on MSDOS.
 123      * To do: use the user input buffer as sliding window.
 124      */
 125
 126     ulg window_size;
 127     /* Actual size of window: 2*wSize, except when the user input buffer
 128      * is directly used as sliding window.
 129      */
 130
 131     Posf *prev;
 132     /* Link to older string with same hash index. To limit the size of this
 133      * array to 64K, this link is maintained only for the last 32K strings.
 134      * An index in this array is thus a window index modulo 32K.
 135      */
 136
 137     Posf *head; /* Heads of the hash chains or NIL. */
 138
 139     uInt  ins_h;          /* hash index of string to be inserted */
 140     uInt  hash_size;      /* number of elements in hash table */
 141     uInt  hash_bits;      /* log2(hash_size) */
 142     uInt  hash_mask;      /* hash_size-1 */
 143
 144     uInt  hash_shift;
 145     /* Number of bits by which ins_h must be shifted at each input
 146      * step. It must be such that after MIN_MATCH steps, the oldest
 147      * byte no longer takes part in the hash key, that is:
 148      *   hash_shift * MIN_MATCH >= hash_bits
 149      */
 150
 151     long block_start;
 152     /* Window position at the beginning of the current output block. Gets
 153      * negative when the window is moved backwards.
 154      */
 155
 156     uInt match_length;           /* length of best match */
 157     IPos prev_match;             /* previous match */
 158     int match_available;         /* set if previous match exists */
 159     uInt strstart;               /* start of string to insert */
 160     uInt match_start;            /* start of matching string */
 161     uInt lookahead;              /* number of valid bytes ahead in window */
 162
 163     uInt prev_length;
 164     /* Length of the best match at previous step. Matches not greater than this
 165      * are discarded. This is used in the lazy match evaluation.
 166      */
 167
 168     uInt max_chain_length;
 169     /* To speed up deflation, hash chains are never searched beyond this
 170      * length.  A higher limit improves compression ratio but degrades the
 171      * speed.
 172      */
 173
 174     uInt max_lazy_match;
 175     /* Attempt to find a better match only when the current match is strictly
 176      * smaller than this value. This mechanism is used only for compression
 177      * levels >= 4.
 178      */
 179 #   define max_insert_length  max_lazy_match
 180     /* Insert new strings in the hash table only if the match length is not
 181      * greater than this length. This saves time but degrades compression.
 182      * max_insert_length is used only for compression levels <= 3.
 183      */
 184
 185     int level;    /* compression level (1..9) */
 186     int strategy; /* favor or force Huffman coding*/
 187
 188     uInt good_match;
 189     /* Use a faster search when the previous match is longer than this */
 190
 191     int nice_match; /* Stop searching when current match exceeds this */
 192
 193                 /* used by trees.c: */
 194     /* Didn't use ct_data typedef below to suppress compiler warning */
 195     struct ct_data_s dyn_ltree[HEAP_SIZE];   /* literal and length tree */
 196     struct ct_data_s dyn_dtree[2*D_CODES+1]; /* distance tree */
 197     struct ct_data_s bl_tree[2*BL_CODES+1];  /* Huffman tree for bit lengths */
 198
 199     struct tree_desc_s l_desc;               /* desc. for literal tree */
 200     struct tree_desc_s d_desc;               /* desc. for distance tree */
 201     struct tree_desc_s bl_desc;              /* desc. for bit length tree */
 202
 203     ush bl_count[MAX_BITS+1];
 204     /* number of codes at each bit length for an optimal tree */
 205
 206     int heap[2*L_CODES+1];      /* heap used to build the Huffman trees */
 207     int heap_len;               /* number of elements in the heap */
 208     int heap_max;               /* element of largest frequency */
 209     /* The sons of heap[n] are heap[2*n] and heap[2*n+1]. heap[0] is not used.
 210      * The same heap array is used to build all trees.
 211      */
 212
 213     uch depth[2*L_CODES+1];
 214     /* Depth of each subtree used as tie breaker for trees of equal frequency
 215      */
 216
 217     uchf *l_buf;          /* buffer for literals or lengths */
 218
 219     uInt  lit_bufsize;
 220     /* Size of match buffer for literals/lengths.  There are 4 reasons for
 221      * limiting lit_bufsize to 64K:
 222      *   - frequencies can be kept in 16 bit counters
 223      *   - if compression is not successful for the first block, all input
 224      *     data is still in the window so we can still emit a stored block even
 225      *     when input comes from standard input.  (This can also be done for
 226      *     all blocks if lit_bufsize is not greater than 32K.)
 227      *   - if compression is not successful for a file smaller than 64K, we can
 228      *     even emit a stored file instead of a stored block (saving 5 bytes).
 229      *     This is applicable only for zip (not gzip or zlib).
 230      *   - creating new Huffman trees less frequently may not provide fast
 231      *     adaptation to changes in the input data statistics. (Take for
 232      *     example a binary file with poorly compressible code followed by
 233      *     a highly compressible string table.) Smaller buffer sizes give
 234      *     fast adaptation but have of course the overhead of transmitting
 235      *     trees more frequently.
 236      *   - I can't count above 4
 237      */
 238
 239     uInt last_lit;      /* running index in l_buf */
 240
 241     ushf *d_buf;
 242     /* Buffer for distances. To simplify the code, d_buf and l_buf have
 243      * the same number of elements. To use different lengths, an extra flag
 244      * array would be necessary.
 245      */
 246
 247     ulg opt_len;        /* bit length of current block with optimal trees */
 248     ulg static_len;     /* bit length of current block with static trees */
 249     uInt matches;       /* number of string matches in current block */
 250     uInt insert;        /* bytes at end of window left to insert */
 251
 252 #ifdef DEBUG
 253     ulg compressed_len; /* total bit length of compressed file mod 2^32 */
 254     ulg bits_sent;      /* bit length of compressed data sent mod 2^32 */
 255 #endif
 256
 257     ush bi_buf;
 258     /* Output buffer. bits are inserted starting at the bottom (least
 259      * significant bits).
 260      */
 261     int bi_valid;
 262     /* Number of valid bits in bi_buf.  All bits above the last valid bit
 263      * are always zero.
 264      */
 265
 266     ulg high_water;
 267     /* High water mark offset in window for initialized bytes -- bytes above
 268      * this are set to zero in order to avoid memory check warnings when
 269      * longest match routines access bytes past the input.  This is then
 270      * updated to the new high water mark.
 271      */
 272
 273 } FAR deflate_state;
 274
 275 /* Output a byte on the stream.
 276  * IN assertion: there is enough room in pending_buf.
 277  */
 278 #define put_byte(s, c) {s->pending_buf[s->pending++] = (c);}
 279
 280
 281 #define MIN_LOOKAHEAD (MAX_MATCH+MIN_MATCH+1)
 282 /* Minimum amount of lookahead, except at the end of the input file.
 283  * See deflate.c for comments about the MIN_MATCH+1.
 284  */
 285
 286 #define MAX_DIST(s)  ((s)->w_size-MIN_LOOKAHEAD)
 287 /* In order to simplify the code, particularly on 16 bit machines, match
 288  * distances are limited to MAX_DIST instead of WSIZE.
 289  */
 290
 291 #define WIN_INIT MAX_MATCH
 292 /* Number of bytes after end of data in window to initialize in order to avoid
 293    memory checker errors from longest match routines */
 294
 295         /* in trees.c */
 296 void ZLIB_INTERNAL _tr_init OF((deflate_state *s));
 297 int ZLIB_INTERNAL _tr_tally OF((deflate_state *s, unsigned dist, unsigned lc));
 298 void ZLIB_INTERNAL _tr_flush_block OF((deflate_state *s, charf *buf,
 299                         ulg stored_len, int last));
 300 void ZLIB_INTERNAL _tr_flush_bits OF((deflate_state *s));
 301 void ZLIB_INTERNAL _tr_align OF((deflate_state *s));
 302 void ZLIB_INTERNAL _tr_stored_block OF((deflate_state *s, charf *buf,
 303                         ulg stored_len, int last));
 304
 305 #define d_code(dist) \
 306    ((dist) < 256 ? _dist_code[dist] : _dist_code[256+((dist)>>7)])
 307 /* Mapping from a distance to a distance code. dist is the distance - 1 and
 308  * must not have side effects. _dist_code[256] and _dist_code[257] are never
 309  * used.
 310  */
 311
 312 #ifndef DEBUG
 313 /* Inline versions of _tr_tally for speed: */
 314
 315 #if defined(GEN_TREES_H) || !defined(STDC)
 316   extern uch ZLIB_INTERNAL _length_code[];
 317   extern uch ZLIB_INTERNAL _dist_code[];
 318 #else
 319   extern const uch ZLIB_INTERNAL _length_code[];
 320   extern const uch ZLIB_INTERNAL _dist_code[];
 321 #endif
 322
 323 # define _tr_tally_lit(s, c, flush) \
 324   { uch cc = (c); \
 325     s->d_buf[s->last_lit] = 0; \
 326     s->l_buf[s->last_lit++] = cc; \
 327     s->dyn_ltree[cc].Freq++; \
 328     flush = (s->last_lit == s->lit_bufsize-1); \
 329    }
 330 # define _tr_tally_dist(s, distance, length, flush) \
 331   { uch len = (length); \
 332     ush dist = (distance); \
 333     s->d_buf[s->last_lit] = dist; \
 334     s->l_buf[s->last_lit++] = len; \
 335     dist--; \
 336     s->dyn_ltree[_length_code[len]+LITERALS+1].Freq++; \
 337     s->dyn_dtree[d_code(dist)].Freq++; \
 338     flush = (s->last_lit == s->lit_bufsize-1); \
 339   }
 340 #else
 341 # define _tr_tally_lit(s, c, flush) flush = _tr_tally(s, 0, c)
 342 # define _tr_tally_dist(s, distance, length, flush) \
 343               flush = _tr_tally(s, distance, length)
 344 #endif
 345
 346 #endif /* DEFLATE_H */