huffman_utils.h
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
63
64
65
66
67
68
69
70
71
72
73
74
75
76
77
78
79
80
81
82
83
84
85
86
87
88
89
90
// Copyright 2012 Google Inc. All Rights Reserved.
//
// Use of this source code is governed by a BSD-style license
// that can be found in the COPYING file in the root of the source
// tree. An additional intellectual property rights grant can be found
// in the file PATENTS. All contributing project authors may
// be found in the AUTHORS file in the root of the source tree.
// -----------------------------------------------------------------------------
//
// Utilities for building and looking up Huffman trees.
//
// Author: Urvang Joshi (urvang@google.com)
#ifndef WEBP_UTILS_HUFFMAN_UTILS_H_
#define WEBP_UTILS_HUFFMAN_UTILS_H_
#include <assert.h>
#include "src/webp/format_constants.h"
#include "src/webp/types.h"
#ifdef __cplusplus
extern "C" {
#endif
#define HUFFMAN_TABLE_BITS 8
#define HUFFMAN_TABLE_MASK ((1 << HUFFMAN_TABLE_BITS) - 1)
#define LENGTHS_TABLE_BITS 7
#define LENGTHS_TABLE_MASK ((1 << LENGTHS_TABLE_BITS) - 1)
// Huffman lookup table entry
typedef struct {
uint8_t bits; // number of bits used for this symbol
uint16_t value; // symbol value or table offset
} HuffmanCode;
// long version for holding 32b values
typedef struct {
int bits; // number of bits used for this symbol,
// or an impossible value if not a literal code.
uint32_t value; // 32b packed ARGB value if literal,
// or non-literal symbol otherwise
} HuffmanCode32;
#define HUFFMAN_PACKED_BITS 6
#define HUFFMAN_PACKED_TABLE_SIZE (1u << HUFFMAN_PACKED_BITS)
// Huffman table group.
// Includes special handling for the following cases:
// - is_trivial_literal: one common literal base for RED/BLUE/ALPHA (not GREEN)
// - is_trivial_code: only 1 code (no bit is read from bitstream)
// - use_packed_table: few enough literal symbols, so all the bit codes
// can fit into a small look-up table packed_table[]
// The common literal base, if applicable, is stored in 'literal_arb'.
typedef struct HTreeGroup HTreeGroup;
struct HTreeGroup {
HuffmanCode* htrees[HUFFMAN_CODES_PER_META_CODE];
int is_trivial_literal; // True, if huffman trees for Red, Blue & Alpha
// Symbols are trivial (have a single code).
uint32_t literal_arb; // If is_trivial_literal is true, this is the
// ARGB value of the pixel, with Green channel
// being set to zero.
int is_trivial_code; // true if is_trivial_literal with only one code
int use_packed_table; // use packed table below for short literal code
// table mapping input bits to a packed values, or escape case to literal code
HuffmanCode32 packed_table[HUFFMAN_PACKED_TABLE_SIZE];
};
// Creates the instance of HTreeGroup with specified number of tree-groups.
HTreeGroup* VP8LHtreeGroupsNew(int num_htree_groups);
// Releases the memory allocated for HTreeGroup.
void VP8LHtreeGroupsFree(HTreeGroup* const htree_groups);
// Builds Huffman lookup table assuming code lengths are in symbol order.
// The 'code_lengths' is pre-allocated temporary memory buffer used for creating
// the huffman table.
// Returns built table size or 0 in case of error (invalid tree or
// memory error).
// If root_table is NULL, it returns 0 if a lookup cannot be built, something
// > 0 otherwise (but not the table size).
int VP8LBuildHuffmanTable(HuffmanCode* const root_table, int root_bits,
const int code_lengths[], int code_lengths_size);
#ifdef __cplusplus
} // extern "C"
#endif
#endif // WEBP_UTILS_HUFFMAN_UTILS_H_