Archipelago » qemu

/*

 * 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-common.h"

#include "include/migration/migration.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, xor;

    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 */

            long mask = (long)0x0101010101010101ULL;

            while (i < slen) {

                xor = *(long *)(old_buf + i) ^ *(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;

}