1// Copyright 2011 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// Author: Jyrki Alakuijala (jyrki@google.com)
11//
12// Entropy encoding (Huffman) for webp lossless
13
14#ifndef WEBP_UTILS_HUFFMAN_ENCODE_H_
15#define WEBP_UTILS_HUFFMAN_ENCODE_H_
16
17#include "../webp/types.h"
18
19#ifdef __cplusplus
20extern "C" {
21#endif
22
23// Struct for holding the tree header in coded form.
24typedef struct {
25  uint8_t code;         // value (0..15) or escape code (16,17,18)
26  uint8_t extra_bits;   // extra bits for escape codes
27} HuffmanTreeToken;
28
29// Struct to represent the tree codes (depth and bits array).
30typedef struct {
31  int       num_symbols;   // Number of symbols.
32  uint8_t*  code_lengths;  // Code lengths of the symbols.
33  uint16_t* codes;         // Symbol Codes.
34} HuffmanTreeCode;
35
36// Struct to represent the Huffman tree.
37// TODO(vikasa): Add comment for the fields of the Struct.
38typedef struct {
39  uint32_t total_count_;
40  int value_;
41  int pool_index_left_;    // Index for the left sub-tree.
42  int pool_index_right_;   // Index for the right sub-tree.
43} HuffmanTree;
44
45// Turn the Huffman tree into a token sequence.
46// Returns the number of tokens used.
47int VP8LCreateCompressedHuffmanTree(const HuffmanTreeCode* const tree,
48                                    HuffmanTreeToken* tokens, int max_tokens);
49
50// Create an optimized tree, and tokenize it.
51// 'buf_rle' and 'huff_tree' are pre-allocated and the 'tree' is the constructed
52// huffman code tree.
53void VP8LCreateHuffmanTree(uint32_t* const histogram, int tree_depth_limit,
54                           uint8_t* const buf_rle, HuffmanTree* const huff_tree,
55                           HuffmanTreeCode* const tree);
56
57#ifdef __cplusplus
58}
59#endif
60
61#endif  // WEBP_UTILS_HUFFMAN_ENCODE_H_
62