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/*
* patch-delta.c:
* recreate a buffer from a source and the delta produced by diff-delta.c
*
* (C) 2005 Nicolas Pitre <nico@cam.org>
*
* This code is free software; you can redistribute it and/or modify
* it under the terms of the GNU General Public License version 2 as
* published by the Free Software Foundation.
*/

#include <stdlib.h>
#include <string.h>
#include "delta.h"

void *patch_delta(void *src_buf, unsigned long src_size,
void *delta_buf, unsigned long delta_size,
unsigned long *dst_size)
{
const unsigned char *data, *top;
unsigned char *dst_buf, *out, cmd;
unsigned long size;

if (delta_size < DELTA_SIZE_MIN)
return NULL;

data = delta_buf;
top = delta_buf + delta_size;

/* make sure the orig file size matches what we expect */
size = get_delta_hdr_size(&data);
if (size != src_size)
return NULL;

/* now the result size */
size = get_delta_hdr_size(&data);
dst_buf = malloc(size + 1);
if (!dst_buf)
return NULL;
dst_buf[size] = 0;

out = dst_buf;
while (data < top) {
cmd = *data++;
if (cmd & 0x80) {
unsigned long cp_off = 0, cp_size = 0;
const unsigned char *buf;
if (cmd & 0x01) cp_off = *data++;
if (cmd & 0x02) cp_off |= (*data++ << 8);
if (cmd & 0x04) cp_off |= (*data++ << 16);
if (cmd & 0x08) cp_off |= (*data++ << 24);
if (cmd & 0x10) cp_size = *data++;
if (cmd & 0x20) cp_size |= (*data++ << 8);
if (cp_size == 0) cp_size = 0x10000;
buf = (cmd & 0x40) ? dst_buf : src_buf;
memcpy(out, buf + cp_off, cp_size);
out += cp_size;
} else {
memcpy(out, data, cmd);
out += cmd;
data += cmd;
}
}

/* sanity check */
if (data != top || out - dst_buf != size) {
free(dst_buf);
return NULL;
}

*dst_size = size;
return dst_buf;
}
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