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      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 // TODO(vikasa): Add comment for the fields of the Struct.
     38 typedef 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.
     47 int 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.
     53 void 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