third_party/libwebp/utils/huffman_encode.h

   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
  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_