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|
/*
* Xor Based Zero Run Length Encoding
*
* Copyright 2013 Red Hat, Inc. and/or its affiliates
*
* Authors:
* Orit Wasserman <owasserm@redhat.com>
*
* This work is licensed under the terms of the GNU GPL, version 2 or later.
* See the COPYING file in the top-level directory.
*
*/
#include "qemu/osdep.h"
#include "qemu/cutils.h"
#include "xbzrle.h"
/*
page = zrun nzrun
| zrun nzrun page
zrun = length
nzrun = length byte...
length = uleb128 encoded integer
*/
int xbzrle_encode_buffer(uint8_t *old_buf, uint8_t *new_buf, int slen,
uint8_t *dst, int dlen)
{
uint32_t zrun_len = 0, nzrun_len = 0;
int d = 0, i = 0;
long res;
uint8_t *nzrun_start = NULL;
g_assert(!(((uintptr_t)old_buf | (uintptr_t)new_buf | slen) %
sizeof(long)));
while (i < slen) {
/* overflow */
if (d + 2 > dlen) {
return -1;
}
/* not aligned to sizeof(long) */
res = (slen - i) % sizeof(long);
while (res && old_buf[i] == new_buf[i]) {
zrun_len++;
i++;
res--;
}
/* word at a time for speed */
if (!res) {
while (i < slen &&
(*(long *)(old_buf + i)) == (*(long *)(new_buf + i))) {
i += sizeof(long);
zrun_len += sizeof(long);
}
/* go over the rest */
while (i < slen && old_buf[i] == new_buf[i]) {
zrun_len++;
i++;
}
}
/* buffer unchanged */
if (zrun_len == slen) {
return 0;
}
/* skip last zero run */
if (i == slen) {
return d;
}
d += uleb128_encode_small(dst + d, zrun_len);
zrun_len = 0;
nzrun_start = new_buf + i;
/* overflow */
if (d + 2 > dlen) {
return -1;
}
/* not aligned to sizeof(long) */
res = (slen - i) % sizeof(long);
while (res && old_buf[i] != new_buf[i]) {
i++;
nzrun_len++;
res--;
}
/* word at a time for speed, use of 32-bit long okay */
if (!res) {
/* truncation to 32-bit long okay */
unsigned long mask = (unsigned long)0x0101010101010101ULL;
while (i < slen) {
unsigned long xor;
xor = *(unsigned long *)(old_buf + i)
^ *(unsigned long *)(new_buf + i);
if ((xor - mask) & ~xor & (mask << 7)) {
/* found the end of an nzrun within the current long */
while (old_buf[i] != new_buf[i]) {
nzrun_len++;
i++;
}
break;
} else {
i += sizeof(long);
nzrun_len += sizeof(long);
}
}
}
d += uleb128_encode_small(dst + d, nzrun_len);
/* overflow */
if (d + nzrun_len > dlen) {
return -1;
}
memcpy(dst + d, nzrun_start, nzrun_len);
d += nzrun_len;
nzrun_len = 0;
}
return d;
}
int xbzrle_decode_buffer(uint8_t *src, int slen, uint8_t *dst, int dlen)
{
int i = 0, d = 0;
int ret;
uint32_t count = 0;
while (i < slen) {
/* zrun */
if ((slen - i) < 2) {
return -1;
}
ret = uleb128_decode_small(src + i, &count);
if (ret < 0 || (i && !count)) {
return -1;
}
i += ret;
d += count;
/* overflow */
if (d > dlen) {
return -1;
}
/* nzrun */
if ((slen - i) < 2) {
return -1;
}
ret = uleb128_decode_small(src + i, &count);
if (ret < 0 || !count) {
return -1;
}
i += ret;
/* overflow */
if (d + count > dlen || i + count > slen) {
return -1;
}
memcpy(dst + d, src + i, count);
d += count;
i += count;
}
return d;
}
|
