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