lzw.h

   1 /* lzw.h -- define the lzw functions.
   2
   3    Copyright (C) 1994-2024 Free Software Foundation, Inc.
   4    Copyright (C) 1992-1993 Jean-loup Gailly.
   5
   6    This program is free software; you can redistribute it and/or modify
   7    it under the terms of the GNU General Public License as published by
   8    the Free Software Foundation; either version 3, or (at your option)
   9    any later version.
  10
  11    This program is distributed in the hope that it will be useful,
  12    but WITHOUT ANY WARRANTY; without even the implied warranty of
  13    MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
  14    GNU General Public License for more details.
  15
  16    You should have received a copy of the GNU General Public License
  17    along with this program.  If not, see <https://www.gnu.org/licenses/>.  */
  18
  19 #ifndef BITS
  20 #  define BITS 16
  21 #endif
  22 #define INIT_BITS 9              /* Initial number of bits per code */
  23
  24 #define LZW_MAGIC  "\037\235"   /* Magic header for lzw files, 1F 9D */
  25
  26 #define BIT_MASK    0x1f /* Mask for 'number of compression bits' */
  27 /* Mask 0x20 is reserved to mean a fourth header byte, and 0x40 is free.
  28  * It's a pity that old uncompress does not check bit 0x20. That makes
  29  * extension of the format actually undesirable because old compress
  30  * would just crash on the new format instead of giving a meaningful
  31  * error message. It does check the number of bits, but it's more
  32  * helpful to say "unsupported format, get a new version" than
  33  * "can only handle 16 bits".
  34  */
  35
  36 #define BLOCK_MODE  0x80
  37 /* Block compression: if table is full and compression rate is dropping,
  38  * clear the dictionary.
  39  */
  40
  41 #define LZW_RESERVED 0x60 /* reserved bits */
  42
  43 #define CLEAR  256       /* flush the dictionary */
  44 #define FIRST  (CLEAR+1) /* first free entry */
  45
  46 extern int maxbits;      /* max bits per code for LZW */
  47
  48 extern int unlzw  (int in, int out);