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@google.com) 13 14#ifndef WEBP_UTILS_HUFFMAN_H_ 15#define WEBP_UTILS_HUFFMAN_H_ 16 17#include <assert.h> 18#include "../webp/types.h" 19 20#if defined(__cplusplus) || defined(c_plusplus) 21extern "C" { 22#endif 23 24// A node of a Huffman tree. 25typedef struct { 26 int symbol_; 27 int children_; // delta offset to both children (contiguous) or 0 if leaf. 28} HuffmanTreeNode; 29 30// Huffman Tree. 31typedef struct HuffmanTree HuffmanTree; 32struct HuffmanTree { 33 HuffmanTreeNode* root_; // all the nodes, starting at root. 34 int max_nodes_; // max number of nodes 35 int num_nodes_; // number of currently occupied nodes 36}; 37 38// Returns true if the given node is a leaf of the Huffman tree. 39static WEBP_INLINE int HuffmanTreeNodeIsLeaf( 40 const HuffmanTreeNode* const node) { 41 return (node->children_ == 0); 42} 43 44// Go down one level. Most critical function. 'right_child' must be 0 or 1. 45static WEBP_INLINE const HuffmanTreeNode* HuffmanTreeNextNode( 46 const HuffmanTreeNode* node, int right_child) { 47 return node + node->children_ + right_child; 48} 49 50// Releases the nodes of the Huffman tree. 51// Note: It does NOT free 'tree' itself. 52void HuffmanTreeRelease(HuffmanTree* const tree); 53 54// Builds Huffman tree assuming code lengths are implicitly in symbol order. 55// Returns false in case of error (invalid tree or memory error). 56int HuffmanTreeBuildImplicit(HuffmanTree* const tree, 57 const int* const code_lengths, 58 int code_lengths_size); 59 60// Build a Huffman tree with explicitly given lists of code lengths, codes 61// and symbols. Verifies that all symbols added are smaller than max_symbol. 62// Returns false in case of an invalid symbol, invalid tree or memory error. 63int HuffmanTreeBuildExplicit(HuffmanTree* const tree, 64 const int* const code_lengths, 65 const int* const codes, 66 const int* const symbols, int max_symbol, 67 int num_symbols); 68 69// Utility: converts Huffman code lengths to corresponding Huffman codes. 70// 'huff_codes' should be pre-allocated. 71// Returns false in case of error (memory allocation, invalid codes). 72int HuffmanCodeLengthsToCodes(const int* const code_lengths, 73 int code_lengths_size, int* const huff_codes); 74 75 76#if defined(__cplusplus) || defined(c_plusplus) 77} // extern "C" 78#endif 79 80#endif // WEBP_UTILS_HUFFMAN_H_ 81