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60 lines
2.1 KiB
60 lines
2.1 KiB
// Copyright 2011 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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// Author: Jyrki Alakuijala (jyrki@google.com) |
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// |
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// Entropy encoding (Huffman) for webp lossless |
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#ifndef WEBP_UTILS_HUFFMAN_ENCODE_H_ |
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#define WEBP_UTILS_HUFFMAN_ENCODE_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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// Struct for holding the tree header in coded form. |
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typedef struct { |
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uint8_t code; // value (0..15) or escape code (16,17,18) |
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uint8_t extra_bits; // extra bits for escape codes |
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} HuffmanTreeToken; |
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// Struct to represent the tree codes (depth and bits array). |
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typedef struct { |
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int num_symbols; // Number of symbols. |
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uint8_t* code_lengths; // Code lengths of the symbols. |
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uint16_t* codes; // Symbol Codes. |
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} HuffmanTreeCode; |
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// Struct to represent the Huffman tree. |
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typedef struct { |
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uint32_t total_count_; // Symbol frequency. |
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int value_; // Symbol value. |
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int pool_index_left_; // Index for the left sub-tree. |
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int pool_index_right_; // Index for the right sub-tree. |
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} HuffmanTree; |
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// Turn the Huffman tree into a token sequence. |
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// Returns the number of tokens used. |
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int VP8LCreateCompressedHuffmanTree(const HuffmanTreeCode* const tree, |
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HuffmanTreeToken* tokens, int max_tokens); |
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// Create an optimized tree, and tokenize it. |
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// 'buf_rle' and 'huff_tree' are pre-allocated and the 'tree' is the constructed |
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// huffman code tree. |
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void VP8LCreateHuffmanTree(uint32_t* const histogram, int tree_depth_limit, |
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uint8_t* const buf_rle, HuffmanTree* const huff_tree, |
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HuffmanTreeCode* const tree); |
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#ifdef __cplusplus |
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} |
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#endif |
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#endif // WEBP_UTILS_HUFFMAN_ENCODE_H_
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