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89 lines
2.6 KiB
C
89 lines
2.6 KiB
C
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// Copyright (c) 2016 The Chromium Authors. All rights reserved.
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// Use of this source code is governed by a BSD-style license that can be
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// found in the LICENSE file.
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#ifndef NET_TOOLS_HUFFMAN_TRIE_TRIE_TRIE_BIT_BUFFER_H_
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#define NET_TOOLS_HUFFMAN_TRIE_TRIE_TRIE_BIT_BUFFER_H_
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#include <stdint.h>
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#include <vector>
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#include "base/macros.h"
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#include "net/tools/huffman_trie/huffman/huffman_builder.h"
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namespace net {
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namespace huffman_trie {
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class BitWriter;
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// TrieBitBuffer acts as a buffer for TrieWriter. It can be used to write bits,
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// characters, and positions. The characters are stored as their
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// HuffmanRepresentation. Positions are references to other locations in the
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// trie.
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class TrieBitBuffer {
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public:
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TrieBitBuffer();
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~TrieBitBuffer();
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// Writes |bit| to the buffer.
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void WriteBit(uint8_t bit);
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// Writes the |number_of_bits| least-significant bits from |bits| to the
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// buffer.
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void WriteBits(uint32_t bits, uint8_t number_of_bits);
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// Write a position to the buffer. Actually writes the difference between
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// |position| and |*last_position|. |*last_position| will be updated to equal
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// the input |position|.
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void WritePosition(uint32_t position, int32_t* last_position);
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// Writes the character in |byte| to the buffer using its Huffman
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// representation in |table|. Optionally tracks usage of the character in
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// |*huffman_builder|.
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void WriteChar(uint8_t byte,
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const HuffmanRepresentationTable& table,
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HuffmanBuilder* huffman_builder);
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// Writes the entire buffer to |*writer|. Returns the position |*writer| was
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// at before the buffer was written to it.
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uint32_t WriteToBitWriter(BitWriter* writer);
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// Appends the buffered bits in |current_byte_| to |elements_|. No padding
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// will occur.
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void Flush();
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private:
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// Represents either the |number_of_bits| least-significant bits in |bits| or
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// a position (offset) in the trie.
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struct BitsOrPosition {
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uint8_t bits;
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uint8_t number_of_bits;
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uint32_t position;
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};
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// Returns the minimum number of bits needed to represent |input|.
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uint8_t BitLength(uint32_t input) const;
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// Append a new element to |elements_|.
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void AppendBitsElement(uint8_t bits, uint8_t number_of_bits);
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void AppendPositionElement(uint32_t position);
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// Buffers bits until they fill a whole byte.
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uint8_t current_byte_ = 0;
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// The number of bits currently in |current_byte_|.
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uint32_t used_ = 0;
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std::vector<BitsOrPosition> elements_;
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DISALLOW_COPY_AND_ASSIGN(TrieBitBuffer);
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};
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} // namespace huffman_trie
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} // namespace net
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#endif // NET_TOOLS_HUFFMAN_TRIE_TRIE_TRIE_BIT_BUFFER_H_
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