src/base/compression/lzss_compression.hh

   1 /*
   2  * Copyright (c) 2003-2005 The Regents of The University of Michigan
   3  * All rights reserved.
   4  *
   5  * Redistribution and use in source and binary forms, with or without
   6  * modification, are permitted provided that the following conditions are
   7  * met: redistributions of source code must retain the above copyright
   8  * notice, this list of conditions and the following disclaimer;
   9  * redistributions in binary form must reproduce the above copyright
  10  * notice, this list of conditions and the following disclaimer in the
  11  * documentation and/or other materials provided with the distribution;
  12  * neither the name of the copyright holders nor the names of its
  13  * contributors may be used to endorse or promote products derived from
  14  * this software without specific prior written permission.
  15  *
  16  * THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS
  17  * "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT
  18  * LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR
  19  * A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT
  20  * OWNER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL,
  21  * SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT
  22  * LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE,
  23  * DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY
  24  * THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
  25  * (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE
  26  * OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
  27  *
  28  * Authors: Erik Hallnor
  29  */
  30
  31 #ifndef __LZSS_COMPRESSION_HH__
  32 #define __LZSS_COMPRESSION_HH__
  33
  34 /** @file
  35  * LZSSCompression declarations.
  36  */
  37
  38 #include "base/compression/base.hh"
  39
  40 /**
  41  * Simple LZSS compression scheme.
  42  */
  43 class LZSSCompression : public CompressionAlgorithm
  44 {
  45     /**
  46      * Finds the longest substring for the given offset.
  47      * @param src The source block that we search for substrings.
  48      * @param back The larger offset.
  49      * @param size The size of the source block.
  50      * @param L The length of the largest substring.
  51      * @param P The starting offset of the largest substring.
  52      */
  53     void findSubString(uint8_t *src, int back, int size, uint16_t &L,
  54                        uint16_t &P);
  55
  56     /**
  57      * Emit an encoded byte to the compressed data array. If the 2 high
  58      * order bits can be signed extended, use 1 byte encoding, if not use 2
  59      * bytes.
  60      * @param dest The compressed data.
  61      * @param byte The byte to emit.
  62      * @return The number of bytes used to encode.
  63      */
  64     int emitByte(uint8_t *dest, uint8_t byte);
  65
  66     /**
  67      * Emit a string reference to the compressed data array. A string reference
  68      * always uses 3 bytes. 1 flag bit, 12 bits for the starting position, and
  69      * 11 bits for the length of the string. This allows compression of 4096
  70      * byte blocks with string lengths of up to 2048 bytes.
  71      * @param dest The compressed data.
  72      * @param P The starting position in the uncompressed data.
  73      * @param L The length in bytes of the string.
  74      */
  75     void emitString(uint8_t *dest, uint16_t P, uint16_t L);
  76
  77   public:
  78     /**
  79      * Compresses the source block and stores it in the destination block. If
  80      * the compressed block grows to larger than the source block, it aborts
  81      * and just performs a copy.
  82      * @param dest The destination block.
  83      * @param src The block to be compressed.
  84      * @param size The size of the source block.
  85      * @return The size of the compressed block.
  86      *
  87      * @pre Destination has enough storage to hold the compressed block.
  88      */
  89     int compress(uint8_t *dest, uint8_t *src, int size);
  90
  91     /**
  92      * Unompresses the source block and stores it in the destination block.
  93      * @param dest The destination block.
  94      * @param src The block to be uncompressed.
  95      * @param size The size of the source block.
  96      * @return The size of the uncompressed block.
  97      *
  98      * @pre Destination has enough storage to hold the uncompressed block.
  99      */
 100     int uncompress(uint8_t *dest, uint8_t *src, int size);
 101 };
 102
 103 #endif //__LZSS_COMPRESSION_HH__