deflate.h

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/* deflate.h -- internal compression state
 * Copyright (C) 1995-2002 Jean-loup Gailly
 * For conditions of distribution and use, see copyright notice in zlib.h
 */

/* WARNING: this file should *not* be used by applications. It is
part of the implementation of the compression library and is
subject to change. Applications should only use zlib.h.
 */

/* @(#) $Id: deflate.h,v 1.1 2005/11/23 14:29:59 stingerx Exp $ */

#ifndef DEFLATE_H
  #define DEFLATE_H

  #include "zutil.h"

  /* define NO_GZIP when compiling if you want to disable gzip header and
  trailer creation by deflate().  NO_GZIP would be used to avoid linking in
  the crc code when it is not needed.  For shared libraries, gzip encoding
  should be left enabled. */
  #ifndef NO_GZIP
    #define GZIP
  #endif

  /* ===========================================================================
   * Internal compression state.
   */

  #define LENGTH_CODES 29
  /* number of length codes, not counting the special END_BLOCK code */

  #define LITERALS  256
  /* number of literal bytes 0..255 */

  #define L_CODES (LITERALS+1+LENGTH_CODES)
  /* number of Literal or Length codes, including the END_BLOCK code */

  #define D_CODES   30
  /* number of distance codes */

  #define BL_CODES  19
  /* number of codes used to transfer the bit lengths */

  #define HEAP_SIZE (2*L_CODES+1)
  /* maximum heap size */

  #define MAX_BITS 15
  /* All codes must not exceed MAX_BITS bits */

  #define INIT_STATE    42
  #define BUSY_STATE   113
  #define FINISH_STATE 666
  /* Stream status */


  /* Data structure describing a single value and its code string. */
  typedef struct ct_data_s
  {
    union
    {
      WORD freq; /* frequency count */
      WORD code; /* bit string */
    } fc;
    union
    {
      WORD dad; /* father node in Huffman tree */
      WORD len; /* length of bit string */
    } dl;
  }
  ct_data;

  #define Freq fc.freq
  #define Code fc.code
  #define Dad  dl.dad
  #define Len  dl.len

  typedef struct static_tree_desc_s static_tree_desc;

  typedef struct tree_desc_s
  {
    ct_data *dyn_tree; /* the dynamic tree */
    int max_code; /* largest code with non zero frequency */
    static_tree_desc *stat_desc; /* the corresponding static tree */
  } FAR tree_desc;

  typedef WORD Pos;
  typedef Pos FAR Posf;
  typedef unsigned IPos;

  /* A Pos is an index in the character window. We use short instead of int to
   * save space in the various tables. IPos is used only for parameter passing.
   */

  typedef struct internal_state
  {
    z_streamp strm; /* pointer back to this zlib stream */
    int status; /* as the name implies */
    BYTE *pending_buf; /* output still pending */
    DWORD pending_buf_size; /* size of pending_buf */
    Bytef *pending_out; /* next pending byte to output to the stream */
    int pending; /* nb of bytes in the pending buffer */
    int wrap; /* bit 0 true for zlib, bit 1 true for gzip */
    Byte data_type; /* UNKNOWN, BINARY or ASCII */
    Byte method; /* STORED (for zip only) or DEFLATED */
    int last_flush; /* value of flush param for previous deflate call */

    /* used by deflate.c: */

    uInt w_size; /* LZ77 window size (32K by default) */
    uInt w_bits; /* log2(w_size)  (8..16) */
    uInt w_mask; /* w_size - 1 */

    Bytef *window;
    /* Sliding window. Input bytes are read into the second half of the window,
     * and move to the first half later to keep a dictionary of at least wSize
     * bytes. With this organization, matches are limited to a distance of
     * wSize-MAX_MATCH bytes, but this ensures that IO is always
     * performed with a length multiple of the block size. Also, it limits
     * the window size to 64K, which is quite useful on MSDOS.
     * To do: use the user input buffer as sliding window.
     */

    DWORD window_size;
    /* Actual size of window: 2*wSize, except when the user input buffer
     * is directly used as sliding window.
     */

    Posf *prev;
    /* Link to older string with same hash index. To limit the size of this
     * array to 64K, this link is maintained only for the last 32K strings.
     * An index in this array is thus a window index modulo 32K.
     */

    Posf *head; /* Heads of the hash chains or NIL. */

    uInt ins_h; /* hash index of string to be inserted */
    uInt hash_size; /* number of elements in hash table */
    uInt hash_bits; /* log2(hash_size) */
    uInt hash_mask; /* hash_size-1 */

    uInt hash_shift;
    /* Number of bits by which ins_h must be shifted at each input
     * step. It must be such that after MIN_MATCH steps, the oldest
     * byte no longer takes part in the hash key, that is:
     *   hash_shift * MIN_MATCH >= hash_bits
     */

    long block_start;
    /* Window position at the beginning of the current output block. Gets
     * negative when the window is moved backwards.
     */

    uInt match_length; /* length of best match */
    IPos prev_match; /* previous match */
    int match_available; /* set if previous match exists */
    uInt strstart; /* start of string to insert */
    uInt match_start; /* start of matching string */
    uInt lookahead; /* number of valid bytes ahead in window */

    uInt prev_length;
    /* Length of the best match at previous step. Matches not greater than this
     * are discarded. This is used in the lazy match evaluation.
     */

    uInt max_chain_length;
    /* To speed up deflation, hash chains are never searched beyond this
     * length.  A higher limit improves compression ratio but degrades the
     * speed.
     */

    uInt max_lazy_match;
    /* Attempt to find a better match only when the current match is strictly
     * smaller than this value. This mechanism is used only for compression
     * levels >= 4.
     */
    #define max_insert_length  max_lazy_match
    /* Insert new strings in the hash table only if the match length is not
     * greater than this length. This saves time but degrades compression.
     * max_insert_length is used only for compression levels <= 3.
     */

    int level; /* compression level (1..9) */
    int strategy; /* favor or force Huffman coding*/

    uInt good_match;
    /* Use a faster search when the previous match is longer than this */

    int nice_match; /* Stop searching when current match exceeds this */

    /* used by trees.c: */
    /* Didn't use ct_data typedef below to supress compiler warning */
    struct ct_data_s dyn_ltree[HEAP_SIZE]; /* literal and length tree */
    struct ct_data_s dyn_dtree[2 *D_CODES + 1]; /* distance tree */
    struct ct_data_s bl_tree[2 *BL_CODES + 1]; /* Huffman tree for bit lengths */

    struct tree_desc_s l_desc; /* desc. for literal tree */
    struct tree_desc_s d_desc; /* desc. for distance tree */
    struct tree_desc_s bl_desc; /* desc. for bit length tree */

    WORD bl_count[MAX_BITS + 1];
    /* number of codes at each bit length for an optimal tree */

    int heap[2 *L_CODES + 1]; /* heap used to build the Huffman trees */
    int heap_len; /* number of elements in the heap */
    int heap_max; /* element of largest frequency */
    /* The sons of heap[n] are heap[2*n] and heap[2*n+1]. heap[0] is not used.
     * The same heap array is used to build all trees.
     */

    BYTE depth[2 *L_CODES + 1];
    /* Depth of each subtree used as tie breaker for trees of equal frequency
     */

    BYTE *l_buf; /* buffer for literals or lengths */

    DWORD lit_bufsize;
    /* Size of match buffer for literals/lengths.  There are 4 reasons for
     * limiting lit_bufsize to 64K:
     *   - frequencies can be kept in 16 bit counters
     *   - if compression is not successful for the first block, all input
     *     data is still in the window so we can still emit a stored block even
     *     when input comes from standard input.  (This can also be done for
     *     all blocks if lit_bufsize is not greater than 32K.)
     *   - if compression is not successful for a file smaller than 64K, we can
     *     even emit a stored file instead of a stored block (saving 5 bytes).
     *     This is applicable only for zip (not gzip or zlib).
     *   - creating new Huffman trees less frequently may not provide fast
     *     adaptation to changes in the input data statistics. (Take for
     *     example a binary file with poorly compressible code followed by
     *     a highly compressible string table.) Smaller buffer sizes give
     *     fast adaptation but have of course the overhead of transmitting
     *     trees more frequently.
     *   - I can't count above 4
     */

    DWORD last_lit; /* running index in l_buf */

    WORD *d_buf;
    /* Buffer for distances. To simplify the code, d_buf and l_buf have
     * the same number of elements. To use different lengths, an extra flag
     * array would be necessary.
     */

    DWORD opt_len; /* bit length of current block with optimal trees */
    DWORD static_len; /* bit length of current block with static trees */
    DWORD matches; /* number of string matches in current block */
    int last_eob_len; /* bit length of EOB code for last block */

    #ifdef DEBUG
      DWORD compressed_len; /* total bit length of compressed file mod 2^32 */
      DWORD bits_sent; /* bit length of compressed data sent mod 2^32 */
    #endif

    WORD bi_buf;
    /* Output buffer. bits are inserted starting at the bottom (least
     * significant bits).
     */
    int bi_valid;
    /* Number of valid bits in bi_buf.  All bits above the last valid bit
     * are always zero.
     */

  } deflate_state;

  /* Output a byte on the stream.
   * IN assertion: there is enough room in pending_buf.
   */
  #define put_byte(s, c) {s->pending_buf[s->pending++] = (c);}


  #define MIN_LOOKAHEAD (MAX_MATCH+MIN_MATCH+1)
  /* Minimum amount of lookahead, except at the end of the input file.
   * See deflate.c for comments about the MIN_MATCH+1.
   */

  #define MAX_DIST(s)  ((s)->w_size-MIN_LOOKAHEAD)
  /* In order to simplify the code, particularly on 16 bit machines, match
   * distances are limited to MAX_DIST instead of WSIZE.
   */

  /* in trees.c */
  void _tr_init OF((deflate_state *s));
  int _tr_tally OF((deflate_state *s, DWORD dist, DWORD lc));
  void _tr_flush_block OF((deflate_state *s, BYTE *buf, DWORD stored_len, int eof));
  void _tr_align OF((deflate_state *s));
  void _tr_stored_block OF((deflate_state *s, BYTE *buf, DWORD stored_len, int eof));

  #define d_code(dist) \
  ((dist) < 256 ? _dist_code[dist] : _dist_code[256+((dist)>>7)])
  /* Mapping from a distance to a distance code. dist is the distance - 1 and
   * must not have side effects. _dist_code[256] and _dist_code[257] are never
   * used.
   */

  #ifndef DEBUG
    /* Inline versions of _tr_tally for speed: */

    #if defined(GEN_TREES_H) || !defined(STDC)
      extern uch _length_code[];
      extern uch _dist_code[];
    #else
      extern const BYTE _length_code[];
      extern const BYTE _dist_code[];
    #endif

    #define _tr_tally_lit(s, c, flush) \
    { uch cc = (c); \
    s->d_buf[s->last_lit] = 0; \
    s->l_buf[s->last_lit++] = cc; \
    s->dyn_ltree[cc].Freq++; \
    flush = (s->last_lit == s->lit_bufsize-1); \
    }
    #define _tr_tally_dist(s, distance, length, flush) \
    { uch len = (length); \
    ush dist = (distance); \
    s->d_buf[s->last_lit] = dist; \
    s->l_buf[s->last_lit++] = len; \
    dist--; \
    s->dyn_ltree[_length_code[len]+LITERALS+1].Freq++; \
    s->dyn_dtree[d_code(dist)].Freq++; \
    flush = (s->last_lit == s->lit_bufsize-1); \
    }
  #else
    #define _tr_tally_lit(s, c, flush) flush = _tr_tally(s, 0, c)
    #define _tr_tally_dist(s, distance, length, flush) \
    flush = _tr_tally(s, distance, length)
  #endif

#endif /* DEFLATE_H */