pcompress/bsdiff/rle_encoder.c

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/*
* This file is a part of Pcompress, a chunked parallel multi-
* algorithm lossless compression and decompression program.
*
* Copyright (C) 2012 Moinak Ghosh. All rights reserved.
* Use is subject to license terms.
*
* This program is free software; you can redistribute it and/or
* modify it under the terms of the GNU Lesser General Public
* License as published by the Free Software Foundation; either
* version 3 of the License, or (at your option) any later version.
*
* This program is distributed in the hope that it will be useful,
* but WITHOUT ANY WARRANTY; without even the implied warranty of
* MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
* Lesser General Public License for more details.
*
* moinakg@belenix.org, http://moinakg.wordpress.com/
*
* This RLE encoder is a simple approach to encode long runs of '0'
* bytes that typically are found in a bsdiff patch output. This
* does not encode repeating runs of other characters.
*/
#include <utils.h>
#include <stdio.h>
#define ZERO_MASK (32768)
#define DATA_MASK (32767)
#define COUNT_MAX (32767)
int
zero_rle_encode(const void *const ibuf, const unsigned int ilen,
void *obuf, unsigned int *const olen)
{
unsigned int pos1, pos2;
unsigned short count;
const uchar_t *const ib = ibuf;
uchar_t *ob = obuf;
pos2 = 0;
for (pos1=0; pos1<ilen && pos2<*olen;) {
count = 0;
if (ib[pos1] == 0) {
for (;pos1<ilen && ib[pos1]==0 && count<COUNT_MAX; pos1++) count++;
count |= ZERO_MASK;
*((unsigned short *)(ob + pos2)) = htons(count);
pos2 += 2;
} else {
unsigned int pos3, pos4, cnt, state;
pos3 = pos2;
pos2 += 2;
if (pos2 > *olen) break;
state = 0;
for (;pos1<ilen && pos2<*olen && count<COUNT_MAX;) {
if (ib[pos1] != 0) state = 0;
if (ib[pos1] == 0 && !state) {
cnt = 0;
pos4 = pos1;
state = 1;
// Lookahead if there are at least 4 consecutive zeroes
for (;pos4<ilen && ib[pos4] == 0; pos4++) cnt++;
if (cnt >= 4) break;
}
ob[pos2++] = ib[pos1++];
count++;
}
*((unsigned short *)(ob + pos3)) = htons(count);
}
}
*olen = pos2;
if (pos1 < ilen) {
return (-1);
} else {
return (0);
}
}
int
zero_rle_decode(const void* ibuf, unsigned int ilen,
void* obuf, unsigned int *olen)
{
unsigned int pos1, pos2, i;
unsigned short count;
const uchar_t *ib = ibuf;
uchar_t *ob = obuf;
pos2 = 0;
pos1 = 0;
for (; pos1<ilen && pos2<*olen;) {
count = ntohs(*((unsigned short *)(ib + pos1)));
pos1 += 2;
if (count & ZERO_MASK) {
count &= DATA_MASK;
for (i=0; i<count && pos2<*olen; i++)
ob[pos2++] = 0;
} else {
for (i=0; i<count && pos1<ilen && pos2<*olen; i++)
ob[pos2++] = ib[pos1++];
}
}
i = *olen;
*olen = pos2;
if (pos1 < ilen || pos2 < i) {
return (-1);
} else {
return (0);
}
}