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Diffstat (limited to 'base/compression/lzss_compression.cc')
| -rw-r--r-- | base/compression/lzss_compression.cc | 166 |
1 files changed, 166 insertions, 0 deletions
diff --git a/base/compression/lzss_compression.cc b/base/compression/lzss_compression.cc new file mode 100644 index 000000000..a1933215a --- /dev/null +++ b/base/compression/lzss_compression.cc @@ -0,0 +1,166 @@ +/* + * Copyright (c) 2003 The Regents of The University of Michigan + * All rights reserved. + * + * Redistribution and use in source and binary forms, with or without + * modification, are permitted provided that the following conditions are + * met: redistributions of source code must retain the above copyright + * notice, this list of conditions and the following disclaimer; + * redistributions in binary form must reproduce the above copyright + * notice, this list of conditions and the following disclaimer in the + * documentation and/or other materials provided with the distribution; + * neither the name of the copyright holders nor the names of its + * contributors may be used to endorse or promote products derived from + * this software without specific prior written permission. + * + * THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS + * "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT + * LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR + * A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT + * OWNER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, + * SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT + * LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, + * DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY + * THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT + * (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE + * OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE. + */ + +/** @file + * LZSSCompression definitions. + */ + +#include <assert.h> + +#include "lzss_compression.hh" + +#include "misc.hh" //for fatal + +int +LZSSCompression::findSubString(uint8_t *src, int front, int back, int size) +{ + int subSize = 0; + int max_length = 2048; + if (size - back < max_length) { + max_length = size - back; + } + for (int i = 0; i < max_length; ++i) { + if (src[front+i] != src[back+i]) { + return subSize; + } + ++subSize; + } + return subSize; +} + +int +LZSSCompression::emitByte(uint8_t *dest, uint8_t byte) +{ + if ((byte >> 5 & 0x7) == 0 || (byte >> 5 & 0x7) == 7) { + // If the top 3 bits are the same, emit 00<6bits> + dest[0] = byte & 0x3f; + return 1; + } else { + // emit 01XXXXXX <8 bits> + dest[0] = 0x40; + dest[1] = byte; + return 2; + } +} + +void +LZSSCompression::emitString(uint8_t *dest, uint16_t P, uint16_t L) +{ + // Emit 1<7P> <5P><3L> <8L> + dest[0] = 1<<7 | (P >> 5 & 0x7f); + dest[1] = ((P & 0x1f) << 3) | (L>>8 & 0x3); + dest[2] = L & 0xFF; +} + +int +LZSSCompression::compress(uint8_t *dest, uint8_t *src, int size) +{ + if (size > 4096) { + fatal("Compression can only handle block sizes of 4096 bytes or less"); + } + + // Encode the first byte. + int dest_index = emitByte(dest, src[0]); + int i = 1; + // A 11 bit field + uint16_t L; + // A 12 bit field + uint16_t P = 0; + + while (i < size && dest_index < size) { + L = 0; + + if (dest_index+3 >= size) { + dest_index = size; + continue; + } + + if (i == size - 1) { + // Output the character + dest_index += emitByte(&dest[dest_index], src[i]); + ++i; + continue; + } + for (int j = 0; j < i; ++j) { + int sub_size = findSubString(src, j, i, size); + if (sub_size >= L) { + L = sub_size; + P = j; + } + } + if (L > 1) { + // Output the string reference + emitString(&dest[dest_index], P, L); + dest_index += 3; + i = i+L; + } else { + // Output the character + dest_index += emitByte(&dest[dest_index], src[i]); + ++i; + } + } + + if (dest_index >= size) { + // Have expansion instead of compression, just copy. + memcpy(dest,src,size); + return size; + } + return dest_index; +} + +int +LZSSCompression::uncompress(uint8_t *dest, uint8_t *src, int size) +{ + int index = 0; + int i = 0; + while (i < size) { + if (src[i] & 1<<7 ) { + // We have a string + // Extract P + int start = (src[i] & 0x3f)<<5 | ((src[i+1] >> 3) & 0x1f); + // Extract L + int len = (src[i+1] & 0x07)<<8 | src[i+2]; + i += 3; + for (int j = start; j < start+len; ++j) { + dest[index++] = dest[j]; + } + } else { + // We have a character + if (src[i] & 1<<6) { + // Value is in the next byte + dest[index++] = src[i+1]; + i += 2; + } else { + // just extend the lower 6 bits + dest[index++] = (src[i] & 0x3f) | ((src[i] & 1<<5) ? 0xC0 : 0); + ++i; + } + } + } + return index; +} |