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/types.h" 19 20 #if defined(__cplusplus) || defined(c_plusplus) 21 extern "C" { 22 #endif 23 24 // A node of a Huffman tree. 25 typedef struct { 26 int symbol_; 27 int children_; // delta offset to both children (contiguous) or 0 if leaf. 28 } HuffmanTreeNode; 29 30 // Huffman Tree. 31 typedef struct HuffmanTree HuffmanTree; 32 struct 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. 39 static 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. 45 static 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. 52 void 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). 56 int 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. 63 int 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). 72 int 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
