jchuff.h revision c6a7fc661d57f86ac08cd637abc881cbe687b11a 
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
27typedef 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 */
41EXTERN(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 */
46EXTERN(void) jpeg_gen_optimal_table
47	JPP((j_compress_ptr cinfo, JHUFF_TBL * htbl, long freq[]));
48