1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
63
64
65
66
67
68
69
70
71
72
73
74
75
76
77
78
79
80
81
82
83
84
85
86
87
88
89
90
91
92
|
/*= -*- 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.h>
#include <assert.h>
#include <stdlib.h>
#include <stdio.h>
#include "rsync.h"
#include "checksum.h"
/* We should make this something other than zero to improve the
* checksum algorithm: tridge suggests a prime number. */
#define CHAR_OFFSET 31
/* 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 * CHAR_OFFSET;
s1 += (buf[i + 0] + buf[i + 1] + buf[i + 2] + buf[i + 3] +
4 * CHAR_OFFSET);
}
for (; i < len; i++) {
s1 += (buf[i] + 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.
*
* 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_t m;
rs_mdfour_begin(&m);
rs_mdfour_update(&m, buf, len);
rs_mdfour_result(&m, (unsigned char *) sum);
}
|
