compiler/libjpeg/main/jchuff.h

   1 /*
   2     $Id$
   3 */
   4
   5 /*
   6  * jchuff.h
   7  *
   8  * Copyright (C) 1991-1997, Thomas G. Lane.
   9  * This file is part of the Independent JPEG Group's software.
  10  * For conditions of distribution and use, see the accompanying README file.
  11  *
  12  * This file contains declarations for Huffman entropy encoding routines
  13  * that are shared between the sequential encoder (jchuff.c) and the
  14  * progressive encoder (jcphuff.c).  No other modules need to see these.
  15  */
  16
  17 /* The legal range of a DCT coefficient is
  18  *  -1024 .. +1023  for 8-bit data;
  19  * -16384 .. +16383 for 12-bit data.
  20  * Hence the magnitude should always fit in 10 or 14 bits respectively.
  21  */
  22
  23 #if BITS_IN_JSAMPLE == 8
  24 #define MAX_COEF_BITS 10
  25 #else
  26 #define MAX_COEF_BITS 14
  27 #endif
  28
  29 /* The legal range of a spatial difference is
  30  * -32767 .. +32768.
  31  * Hence the magnitude should always fit in 16 bits.
  32  */
  33
  34 #define MAX_DIFF_BITS 16
  35
  36 /* Derived data constructed for each Huffman table */
  37
  38 typedef struct {
  39   unsigned int ehufco[256];     /* code for each symbol */
  40   char ehufsi[256];             /* length of code for each symbol */
  41   /* If no code has been allocated for a symbol S, ehufsi[S] contains 0 */
  42 } c_derived_tbl;
  43
  44 /* Short forms of external names for systems with brain-damaged linkers. */
  45
  46 #ifdef NEED_SHORT_EXTERNAL_NAMES
  47 #define jpeg_make_c_derived_tbl jMkCDerived
  48 #define jpeg_gen_optimal_table  jGenOptTbl
  49 #endif /* NEED_SHORT_EXTERNAL_NAMES */
  50
  51 /* Expand a Huffman table definition into the derived format */
  52 JEXTERN(void) jpeg_make_c_derived_tbl
  53         JPP((j_compress_ptr cinfo, boolean isDC, int tblno,
  54              c_derived_tbl ** pdtbl));
  55
  56 /* Generate an optimal table definition given the specified counts */
  57 JEXTERN(void) jpeg_gen_optimal_table
  58         JPP((j_compress_ptr cinfo, JHUFF_TBL * htbl, long freq[]));