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