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- // 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_
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