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_UTILS_H_
15 #define WEBP_UTILS_HUFFMAN_ENCODE_UTILS_H_
16 
17 #include "src/webp/types.h"
18 
19 #ifdef __cplusplus
20 extern "C" {
21 #endif
22 
23 // Struct for holding the tree header in coded form.
24 typedef 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).
30 typedef 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 typedef struct {
38   uint32_t total_count_;   // Symbol frequency.
39   int value_;              // Symbol value.
40   int pool_index_left_;    // Index for the left sub-tree.
41   int pool_index_right_;   // Index for the right sub-tree.
42 } HuffmanTree;
43 
44 // Turn the Huffman tree into a token sequence.
45 // Returns the number of tokens used.
46 int VP8LCreateCompressedHuffmanTree(const HuffmanTreeCode* const tree,
47                                     HuffmanTreeToken* tokens, int max_tokens);
48 
49 // Create an optimized tree, and tokenize it.
50 // 'buf_rle' and 'huff_tree' are pre-allocated and the 'tree' is the constructed
51 // huffman code tree.
52 void VP8LCreateHuffmanTree(uint32_t* const histogram, int tree_depth_limit,
53                            uint8_t* const buf_rle, HuffmanTree* const huff_tree,
54                            HuffmanTreeCode* const tree);
55 
56 #ifdef __cplusplus
57 }
58 #endif
59 
60 #endif  // WEBP_UTILS_HUFFMAN_ENCODE_UTILS_H_
61