jpeg/jchuff.h

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