| -rw-r--r-- | rsync/checksum.c | 81 |
1 files changed, 81 insertions, 0 deletions
diff --git a/rsync/checksum.c b/rsync/checksum.c new file mode 100644 index 0000000..eab9e46 --- a/dev/null +++ b/rsync/checksum.c @@ -0,0 +1,81 @@ +/*= -*- c-basic-offset: 4; indent-tabs-mode: nil; -*- + * + * librsync -- the library for network deltas + * $Id$ + * + * Copyright (C) 1999, 2000, 2001 by Martin Pool <mbp@samba.org> + * Copyright (C) 1996 by Andrew Tridgell + * Copyright (C) 1996 by Paul Mackerras + * + * 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 2.1 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. + * + * You should have received a copy of the GNU Lesser General Public License + * along with this program; if not, write to the Free Software + * Foundation, Inc., 675 Mass Ave, Cambridge, MA 02139, USA. + */ + +#include <config_rsync.h> + +#include <assert.h> +#include <stdlib.h> +#include <stdio.h> + +#include "rsync.h" +#include "checksum.h" + + +/* This can possibly be used to restart the checksum system in the + * case where we detected corruption. I'm not sure yet how to make + * this useful in librsync. */ +int checksum_seed = 0; + +/* + * A simple 32 bit checksum that can be updated from either end + * (inspired by Mark Adler's Adler-32 checksum) + */ +unsigned int rs_calc_weak_sum(void const *p, int len) +{ + int i; + unsigned s1, s2; + unsigned char const *buf = (unsigned char const *) p; + + s1 = s2 = 0; + for (i = 0; i < (len - 4); i += 4) { + s2 += 4 * (s1 + buf[i]) + 3 * buf[i + 1] + + 2 * buf[i + 2] + buf[i + 3] + 10 * RS_CHAR_OFFSET; + s1 += (buf[i + 0] + buf[i + 1] + buf[i + 2] + buf[i + 3] + + 4 * RS_CHAR_OFFSET); + } + for (; i < len; i++) { + s1 += (buf[i] + RS_CHAR_OFFSET); + s2 += s1; + } + return (s1 & 0xffff) + (s2 << 16); +} + + +/** + * Calculate and store into SUM a strong MD4 checksum of the file + * blocks seen so far. + * + * In plain rsync, the checksum is perturbed by a seed value. This is + * used when retrying a failed transmission: we've discovered that the + * hashes collided at some point, so we're going to try again with + * different hashes to see if we can get it right. (Check tridge's + * thesis for details and to see if that's correct.) + * + * Since we can't retry a web transaction I'm not sure if it's very + * useful in rproxy. + */ +void rs_calc_strong_sum(void const *buf, size_t len, rs_strong_sum_t *sum) +{ + rs_mdfour((unsigned char *) sum, buf, len); +} |