| // Copyright 2012 Google Inc. All Rights Reserved. |
| // |
| // Use of this source code is governed by a BSD-style license |
| // that can be found in the COPYING file in the root of the source |
| // tree. An additional intellectual property rights grant can be found |
| // in the file PATENTS. All contributing project authors may |
| // be found in the AUTHORS file in the root of the source tree. |
| // ----------------------------------------------------------------------------- |
| // |
| // Utilities for building and looking up Huffman trees. |
| // |
| // Author: Urvang Joshi (urvang@google.com) |
| |
| #ifndef WEBP_UTILS_HUFFMAN_H_ |
| #define WEBP_UTILS_HUFFMAN_H_ |
| |
| #include <assert.h> |
| #include "webp/format_constants.h" |
| #include "webp/types.h" |
| |
| #ifdef __cplusplus |
| extern "C" { |
| #endif |
| |
| // A node of a Huffman tree. |
| typedef struct { |
| int symbol_; |
| int children_; // delta offset to both children (contiguous) or 0 if leaf. |
| } HuffmanTreeNode; |
| |
| // Huffman Tree. |
| #define HUFF_LUT_BITS 7 |
| #define HUFF_LUT (1U << HUFF_LUT_BITS) |
| typedef struct HuffmanTree HuffmanTree; |
| struct HuffmanTree { |
| // Fast lookup for short bit lengths. |
| uint8_t lut_bits_[HUFF_LUT]; |
| int16_t lut_symbol_[HUFF_LUT]; |
| int16_t lut_jump_[HUFF_LUT]; |
| // Complete tree for lookups. |
| HuffmanTreeNode* root_; // all the nodes, starting at root. |
| int max_nodes_; // max number of nodes |
| int num_nodes_; // number of currently occupied nodes |
| }; |
| |
| // Huffman Tree group. |
| typedef struct HTreeGroup HTreeGroup; |
| struct HTreeGroup { |
| HuffmanTree htrees_[HUFFMAN_CODES_PER_META_CODE]; |
| }; |
| |
| // Returns true if the given node is not a leaf of the Huffman tree. |
| static WEBP_INLINE int HuffmanTreeNodeIsNotLeaf( |
| const HuffmanTreeNode* const node) { |
| return node->children_; |
| } |
| |
| // Go down one level. Most critical function. 'right_child' must be 0 or 1. |
| static WEBP_INLINE const HuffmanTreeNode* HuffmanTreeNextNode( |
| const HuffmanTreeNode* node, int right_child) { |
| return node + node->children_ + right_child; |
| } |
| |
| // Releases the nodes of the Huffman tree. |
| // Note: It does NOT free 'tree' itself. |
| void VP8LHuffmanTreeFree(HuffmanTree* const tree); |
| |
| // Creates the instance of HTreeGroup with specified number of tree-groups. |
| HTreeGroup* VP8LHtreeGroupsNew(int num_htree_groups); |
| |
| // Releases the memory allocated for HTreeGroup. |
| void VP8LHtreeGroupsFree(HTreeGroup* htree_groups, int num_htree_groups); |
| |
| // Builds Huffman tree assuming code lengths are implicitly in symbol order. |
| // The 'huff_codes' and 'code_lengths' are pre-allocated temporary memory |
| // buffers, used for creating the huffman tree. |
| // Returns false in case of error (invalid tree or memory error). |
| int VP8LHuffmanTreeBuildImplicit(HuffmanTree* const tree, |
| const int* const code_lengths, |
| int* const huff_codes, |
| int code_lengths_size); |
| |
| // Build a Huffman tree with explicitly given lists of code lengths, codes |
| // and symbols. Verifies that all symbols added are smaller than max_symbol. |
| // Returns false in case of an invalid symbol, invalid tree or memory error. |
| int VP8LHuffmanTreeBuildExplicit(HuffmanTree* const tree, |
| const int* const code_lengths, |
| const int* const codes, |
| const int* const symbols, int max_symbol, |
| int num_symbols); |
| |
| // Utility: converts Huffman code lengths to corresponding Huffman codes. |
| // 'huff_codes' should be pre-allocated. |
| // Returns false in case of error (memory allocation, invalid codes). |
| int VP8LHuffmanCodeLengthsToCodes(const int* const code_lengths, |
| int code_lengths_size, int* const huff_codes); |
| |
| #ifdef __cplusplus |
| } // extern "C" |
| #endif |
| |
| #endif // WEBP_UTILS_HUFFMAN_H_ |