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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 (
#include <assert.h>
#include "../webp/format_constants.h"
#include "../webp/types.h"
#ifdef __cplusplus
extern "C" {
// 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 {
// 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"