lzw.h

   1 /* lzw.h -- define the lzw functions.
   2
   3    Copyright (C) 1992-1993 Jean-loup Gailly.
   4
   5    This program is free software; you can redistribute it and/or modify
   6    it under the terms of the GNU General Public License as published by
   7    the Free Software Foundation; either version 3, or (at your option)
   8    any later version.
   9
  10    This program is distributed in the hope that it will be useful,
  11    but WITHOUT ANY WARRANTY; without even the implied warranty of
  12    MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
  13    GNU General Public License for more details.
  14
  15    You should have received a copy of the GNU General Public License
  16    along with this program; if not, write to the Free Software Foundation,
  17    Inc., 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301, USA.  */
  18
  19 #if !defined(OF) && defined(lint)
  20 #  include "gzip.h"
  21 #endif
  22
  23 #ifndef BITS
  24 #  define BITS 16
  25 #endif
  26 #define INIT_BITS 9              /* Initial number of bits per code */
  27
  28 #define LZW_MAGIC  "\037\235"   /* Magic header for lzw files, 1F 9D */
  29
  30 #define BIT_MASK    0x1f /* Mask for 'number of compression bits' */
  31 /* Mask 0x20 is reserved to mean a fourth header byte, and 0x40 is free.
  32  * It's a pity that old uncompress does not check bit 0x20. That makes
  33  * extension of the format actually undesirable because old compress
  34  * would just crash on the new format instead of giving a meaningful
  35  * error message. It does check the number of bits, but it's more
  36  * helpful to say "unsupported format, get a new version" than
  37  * "can only handle 16 bits".
  38  */
  39
  40 #define BLOCK_MODE  0x80
  41 /* Block compression: if table is full and compression rate is dropping,
  42  * clear the dictionary.
  43  */
  44
  45 #define LZW_RESERVED 0x60 /* reserved bits */
  46
  47 #define CLEAR  256       /* flush the dictionary */
  48 #define FIRST  (CLEAR+1) /* first free entry */
  49
  50 extern int maxbits;      /* max bits per code for LZW */
  51 extern int block_mode;   /* block compress mode -C compatible with 2.0 */
  52
  53 extern int lzw    OF((int in, int out));
  54 extern int unlzw  OF((int in, int out));