base/compression/lzss_compression.cc: base/compression/lzss_compression.hh: Rework for better performance --HG-- extra : convert_revision : b13d706e0e23cbe7122b611258354c66cf5f3c70
101 lines
4 KiB
C++
101 lines
4 KiB
C++
/*
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* Copyright (c) 2003 The Regents of The University of Michigan
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* All rights reserved.
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*
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* Redistribution and use in source and binary forms, with or without
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* modification, are permitted provided that the following conditions are
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* met: redistributions of source code must retain the above copyright
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* notice, this list of conditions and the following disclaimer;
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* redistributions in binary form must reproduce the above copyright
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* notice, this list of conditions and the following disclaimer in the
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* documentation and/or other materials provided with the distribution;
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* neither the name of the copyright holders nor the names of its
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* contributors may be used to endorse or promote products derived from
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* this software without specific prior written permission.
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*
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* THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS
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* "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT
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* LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR
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* A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT
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* OWNER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL,
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* SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT
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* LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE,
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* DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY
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* THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
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* (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE
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* OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
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*/
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#ifndef __LZSS_COMPRESSION_HH__
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#define __LZSS_COMPRESSION_HH__
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/** @file
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* LZSSCompression declarations.
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*/
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#include "sim/host.hh" // for uint8_t
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/**
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* Simple LZSS compression scheme.
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*/
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class LZSSCompression
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{
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/**
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* Finds the longest substring for the given offset.
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* @param src The source block that we search for substrings.
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* @param back The larger offset.
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* @param size The size of the source block.
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* @param L The length of the largest substring.
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* @param P The starting offset of the largest substring.
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*/
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void findSubString(uint8_t *src, int back, int size, uint16_t &L,
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uint16_t &P);
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/**
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* Emit an encoded byte to the compressed data array. If the 2 high
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* order bits can be signed extended, use 1 byte encoding, if not use 2
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* bytes.
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* @param dest The compressed data.
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* @param byte The byte to emit.
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* @return The number of bytes used to encode.
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*/
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int emitByte(uint8_t *dest, uint8_t byte);
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/**
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* Emit a string reference to the compressed data array. A string reference
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* always uses 3 bytes. 1 flag bit, 12 bits for the starting position, and
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* 11 bits for the length of the string. This allows compression of 4096
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* byte blocks with string lengths of up to 2048 bytes.
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* @param dest The compressed data.
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* @param P The starting position in the uncompressed data.
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* @param L The length in bytes of the string.
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*/
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void emitString(uint8_t *dest, uint16_t P, uint16_t L);
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public:
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/**
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* Compresses the source block and stores it in the destination block. If
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* the compressed block grows to larger than the source block, it aborts
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* and just performs a copy.
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* @param dest The destination block.
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* @param src The block to be compressed.
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* @param size The size of the source block.
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* @return The size of the compressed block.
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*
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* @pre Destination has enough storage to hold the compressed block.
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*/
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int compress(uint8_t *dest, uint8_t *src, int size);
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/**
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* Unompresses the source block and stores it in the destination block.
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* @param dest The destination block.
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* @param src The block to be uncompressed.
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* @param size The size of the source block.
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* @return The size of the uncompressed block.
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*
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* @pre Destination has enough storage to hold the uncompressed block.
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*/
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int uncompress(uint8_t *dest, uint8_t *src, int size);
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};
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#endif //__LZSS_COMPRESSION_HH__
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