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 (at) 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 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_H_ 61
