1  /* lzw.h -- define the lzw functions.
       2  
       3     Copyright (C) 1994-2023 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, write to the Free Software Foundation,
      18     Inc., 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301, USA.  */
      19  
      20  #ifndef BITS
      21  #  define BITS 16
      22  #endif
      23  #define INIT_BITS 9              /* Initial number of bits per code */
      24  
      25  #define	LZW_MAGIC  "\037\235"   /* Magic header for lzw files, 1F 9D */
      26  
      27  #define BIT_MASK    0x1f /* Mask for 'number of compression bits' */
      28  /* Mask 0x20 is reserved to mean a fourth header byte, and 0x40 is free.
      29   * It's a pity that old uncompress does not check bit 0x20. That makes
      30   * extension of the format actually undesirable because old compress
      31   * would just crash on the new format instead of giving a meaningful
      32   * error message. It does check the number of bits, but it's more
      33   * helpful to say "unsupported format, get a new version" than
      34   * "can only handle 16 bits".
      35   */
      36  
      37  #define BLOCK_MODE  0x80
      38  /* Block compression: if table is full and compression rate is dropping,
      39   * clear the dictionary.
      40   */
      41  
      42  #define LZW_RESERVED 0x60 /* reserved bits */
      43  
      44  #define	CLEAR  256       /* flush the dictionary */
      45  #define FIRST  (CLEAR+1) /* first free entry */
      46  
      47  extern int maxbits;      /* max bits per code for LZW */
      48  
      49  extern int unlzw  (int in, int out);