79 lines
2.8 KiB
C
79 lines
2.8 KiB
C
// Copyright 2012 Google Inc. All Rights Reserved.
|
|
//
|
|
// This code is licensed under the same terms as WebM:
|
|
// Software License Agreement: http://www.webmproject.org/license/software/
|
|
// Additional IP Rights Grant: http://www.webmproject.org/license/additional/
|
|
// -----------------------------------------------------------------------------
|
|
//
|
|
// 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/types.h"
|
|
|
|
#if defined(__cplusplus) || defined(c_plusplus)
|
|
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.
|
|
typedef struct HuffmanTree HuffmanTree;
|
|
struct HuffmanTree {
|
|
HuffmanTreeNode* root_; // all the nodes, starting at root.
|
|
int max_nodes_; // max number of nodes
|
|
int num_nodes_; // number of currently occupied nodes
|
|
};
|
|
|
|
// Returns true if the given node is a leaf of the Huffman tree.
|
|
static WEBP_INLINE int HuffmanTreeNodeIsLeaf(
|
|
const HuffmanTreeNode* const node) {
|
|
return (node->children_ == 0);
|
|
}
|
|
|
|
// 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 HuffmanTreeRelease(HuffmanTree* const tree);
|
|
|
|
// Builds Huffman tree assuming code lengths are implicitly in symbol order.
|
|
// Returns false in case of error (invalid tree or memory error).
|
|
int HuffmanTreeBuildImplicit(HuffmanTree* const tree,
|
|
const int* const code_lengths,
|
|
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 HuffmanTreeBuildExplicit(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 HuffmanCodeLengthsToCodes(const int* const code_lengths,
|
|
int code_lengths_size, int* const huff_codes);
|
|
|
|
|
|
#if defined(__cplusplus) || defined(c_plusplus)
|
|
} // extern "C"
|
|
#endif
|
|
|
|
#endif // WEBP_UTILS_HUFFMAN_H_
|