88 lines
3.1 KiB
C
88 lines
3.1 KiB
C
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// Copyright 2012 Google Inc. All Rights Reserved.
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//
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// Use of this source code is governed by a BSD-style license
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// that can be found in the COPYING file in the root of the source
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// tree. An additional intellectual property rights grant can be found
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// in the file PATENTS. All contributing project authors may
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// be found in the AUTHORS file in the root of the source tree.
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// -----------------------------------------------------------------------------
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//
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// Utilities for building and looking up Huffman trees.
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//
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// Author: Urvang Joshi (urvang@google.com)
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#ifndef WEBP_UTILS_HUFFMAN_H_
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#define WEBP_UTILS_HUFFMAN_H_
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#include <assert.h>
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#include "../webp/types.h"
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#ifdef __cplusplus
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extern "C" {
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#endif
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// A node of a Huffman tree.
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typedef struct {
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int symbol_;
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int children_; // delta offset to both children (contiguous) or 0 if leaf.
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} HuffmanTreeNode;
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// Huffman Tree.
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#define HUFF_LUT_BITS 7
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#define HUFF_LUT (1U << HUFF_LUT_BITS)
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typedef struct HuffmanTree HuffmanTree;
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struct HuffmanTree {
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// Fast lookup for short bit lengths.
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uint8_t lut_bits_[HUFF_LUT];
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int16_t lut_symbol_[HUFF_LUT];
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int16_t lut_jump_[HUFF_LUT];
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// Complete tree for lookups.
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HuffmanTreeNode* root_; // all the nodes, starting at root.
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int max_nodes_; // max number of nodes
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int num_nodes_; // number of currently occupied nodes
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};
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// Returns true if the given node is not a leaf of the Huffman tree.
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static WEBP_INLINE int HuffmanTreeNodeIsNotLeaf(
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const HuffmanTreeNode* const node) {
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return node->children_;
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}
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// Go down one level. Most critical function. 'right_child' must be 0 or 1.
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static WEBP_INLINE const HuffmanTreeNode* HuffmanTreeNextNode(
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const HuffmanTreeNode* node, int right_child) {
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return node + node->children_ + right_child;
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}
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// Releases the nodes of the Huffman tree.
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// Note: It does NOT free 'tree' itself.
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void HuffmanTreeRelease(HuffmanTree* const tree);
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// Builds Huffman tree assuming code lengths are implicitly in symbol order.
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// Returns false in case of error (invalid tree or memory error).
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int HuffmanTreeBuildImplicit(HuffmanTree* const tree,
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const int* const code_lengths,
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int code_lengths_size);
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// Build a Huffman tree with explicitly given lists of code lengths, codes
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// and symbols. Verifies that all symbols added are smaller than max_symbol.
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// Returns false in case of an invalid symbol, invalid tree or memory error.
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int HuffmanTreeBuildExplicit(HuffmanTree* const tree,
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const int* const code_lengths,
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const int* const codes,
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const int* const symbols, int max_symbol,
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int num_symbols);
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// Utility: converts Huffman code lengths to corresponding Huffman codes.
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// 'huff_codes' should be pre-allocated.
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// Returns false in case of error (memory allocation, invalid codes).
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int HuffmanCodeLengthsToCodes(const int* const code_lengths,
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int code_lengths_size, int* const huff_codes);
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#ifdef __cplusplus
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} // extern "C"
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#endif
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#endif // WEBP_UTILS_HUFFMAN_H_
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