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