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/*
* Copyright (c) 2003-2005 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.
*
* Authors: Erik Hallnor
*/
/** @file
* LZSSCompression definitions.
*/
#include <assert.h>
#include "base/compression/lzss_compression.hh"
#include "base/misc.hh" //for fatal
void
LZSSCompression::findSubString(uint8_t *src, int back, int size, uint16_t &L,
uint16_t &P)
{
int front = 0;
int max_length = size - back;
L = 0;
P = back - 1;
while (front < back) {
while (src[front] != src[back] && front < back) ++front;
if (front >= back) {
return;
}
int i = 1;
while (src[front+i] == src[back+i] && i < max_length) ++i;
if (i >= L) {
L = i;
P = front;
}
if (src[front+i] != src[back+i-1]) {
// can't find a longer substring until past this point.
front += i;
} else {
++front;
}
}
}
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;
}
findSubString(src, i, size, L, P);
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;
}
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