1 // Copyright 2012 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 // Utilities for building and looking up Huffman trees. 11 // 12 // Author: Urvang Joshi (urvang (at) google.com) 13 14 #ifndef WEBP_UTILS_HUFFMAN_H_ 15 #define WEBP_UTILS_HUFFMAN_H_ 16 17 #include <assert.h> 18 #include "webp/format_constants.h" 19 #include "webp/types.h" 20 21 #ifdef __cplusplus 22 extern "C" { 23 #endif 24 25 // A node of a Huffman tree. 26 typedef struct { 27 int symbol_; 28 int children_; // delta offset to both children (contiguous) or 0 if leaf. 29 } HuffmanTreeNode; 30 31 // Huffman Tree. 32 #define HUFF_LUT_BITS 7 33 #define HUFF_LUT (1U << HUFF_LUT_BITS) 34 typedef struct HuffmanTree HuffmanTree; 35 struct HuffmanTree { 36 // Fast lookup for short bit lengths. 37 uint8_t lut_bits_[HUFF_LUT]; 38 int16_t lut_symbol_[HUFF_LUT]; 39 int16_t lut_jump_[HUFF_LUT]; 40 // Complete tree for lookups. 41 HuffmanTreeNode* root_; // all the nodes, starting at root. 42 int max_nodes_; // max number of nodes 43 int num_nodes_; // number of currently occupied nodes 44 }; 45 46 // Huffman Tree group. 47 typedef struct HTreeGroup HTreeGroup; 48 struct HTreeGroup { 49 HuffmanTree htrees_[HUFFMAN_CODES_PER_META_CODE]; 50 }; 51 52 // Returns true if the given node is not a leaf of the Huffman tree. 53 static WEBP_INLINE int HuffmanTreeNodeIsNotLeaf( 54 const HuffmanTreeNode* const node) { 55 return node->children_; 56 } 57 58 // Go down one level. Most critical function. 'right_child' must be 0 or 1. 59 static WEBP_INLINE const HuffmanTreeNode* HuffmanTreeNextNode( 60 const HuffmanTreeNode* node, int right_child) { 61 return node + node->children_ + right_child; 62 } 63 64 // Releases the nodes of the Huffman tree. 65 // Note: It does NOT free 'tree' itself. 66 void VP8LHuffmanTreeFree(HuffmanTree* const tree); 67 68 // Creates the instance of HTreeGroup with specified number of tree-groups. 69 HTreeGroup* VP8LHtreeGroupsNew(int num_htree_groups); 70 71 // Releases the memory allocated for HTreeGroup. 72 void VP8LHtreeGroupsFree(HTreeGroup* htree_groups, int num_htree_groups); 73 74 // Builds Huffman tree assuming code lengths are implicitly in symbol order. 75 // The 'huff_codes' and 'code_lengths' are pre-allocated temporary memory 76 // buffers, used for creating the huffman tree. 77 // Returns false in case of error (invalid tree or memory error). 78 int VP8LHuffmanTreeBuildImplicit(HuffmanTree* const tree, 79 const int* const code_lengths, 80 int* const huff_codes, 81 int code_lengths_size); 82 83 // Build a Huffman tree with explicitly given lists of code lengths, codes 84 // and symbols. Verifies that all symbols added are smaller than max_symbol. 85 // Returns false in case of an invalid symbol, invalid tree or memory error. 86 int VP8LHuffmanTreeBuildExplicit(HuffmanTree* const tree, 87 const int* const code_lengths, 88 const int* const codes, 89 const int* const symbols, int max_symbol, 90 int num_symbols); 91 92 // Utility: converts Huffman code lengths to corresponding Huffman codes. 93 // 'huff_codes' should be pre-allocated. 94 // Returns false in case of error (memory allocation, invalid codes). 95 int VP8LHuffmanCodeLengthsToCodes(const int* const code_lengths, 96 int code_lengths_size, int* const huff_codes); 97 98 #ifdef __cplusplus 99 } // extern "C" 100 #endif 101 102 #endif // WEBP_UTILS_HUFFMAN_H_ 103
