lzw.h

   1 /* lzw.h -- define the lzw functions.
   2  * Copyright (C) 1992-1993 Jean-loup Gailly.
   3  * This is free software; you can redistribute it and/or modify it under the
   4  * terms of the GNU General Public License, see the file COPYING.
   5  */
   6
   7 #if !defined(OF) && defined(lint)
   8 #  include "gzip.h"
   9 #endif
  10
  11 #ifndef BITS
  12 #  define BITS 16
  13 #endif
  14 #define INIT_BITS 9              /* Initial number of bits per code */
  15
  16 #define LZW_MAGIC  "\037\235"   /* Magic header for lzw files, 1F 9D */
  17
  18 #define BIT_MASK    0x1f /* Mask for 'number of compression bits' */
  19 /* Mask 0x20 is reserved to mean a fourth header byte, and 0x40 is free.
  20  * It's a pity that old uncompress does not check bit 0x20. That makes
  21  * extension of the format actually undesirable because old compress
  22  * would just crash on the new format instead of giving a meaningful
  23  * error message. It does check the number of bits, but it's more
  24  * helpful to say "unsupported format, get a new version" than
  25  * "can only handle 16 bits".
  26  */
  27
  28 #define BLOCK_MODE  0x80
  29 /* Block compression: if table is full and compression rate is dropping,
  30  * clear the dictionary.
  31  */
  32
  33 #define LZW_RESERVED 0x60 /* reserved bits */
  34
  35 #define CLEAR  256       /* flush the dictionary */
  36 #define FIRST  (CLEAR+1) /* first free entry */
  37
  38 extern int maxbits;      /* max bits per code for LZW */
  39 extern int block_mode;   /* block compress mode -C compatible with 2.0 */
  40
  41 extern int lzw    OF((int in, int out));
  42 extern int unlzw  OF((int in, int out));