82 lines
2.7 KiB
C
82 lines
2.7 KiB
C
/*= -*- c-basic-offset: 4; indent-tabs-mode: nil; -*-
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*
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* librsync -- the library for network deltas
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* Id: checksum.c,v 1.34 2001/03/18 10:56:39 mbp Exp
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*
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* Copyright (C) 1999, 2000, 2001 by Martin Pool <mbp@samba.org>
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* Copyright (C) 1996 by Andrew Tridgell
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* Copyright (C) 1996 by Paul Mackerras
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*
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* This program is free software; you can redistribute it and/or modify
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* it under the terms of the GNU Lesser General Public License as published by
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* the Free Software Foundation; either version 2.1 of the License, or
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* (at your option) any later version.
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*
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* This program is distributed in the hope that it will be useful,
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* but WITHOUT ANY WARRANTY; without even the implied warranty of
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* MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
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* GNU Lesser General Public License for more details.
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*
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* You should have received a copy of the GNU Lesser General Public License
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* along with this program; if not, write to the Free Software
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* Foundation, Inc., 675 Mass Ave, Cambridge, MA 02139, USA.
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*/
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#include <config.h>
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#include <assert.h>
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#include <stdlib.h>
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#include <stdio.h>
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#include "rsync.h"
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#include "checksum.h"
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/* This can possibly be used to restart the checksum system in the
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* case where we detected corruption. I'm not sure yet how to make
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* this useful in librsync. */
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int checksum_seed = 0;
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/*
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* A simple 32 bit checksum that can be updated from either end
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* (inspired by Mark Adler's Adler-32 checksum)
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*/
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unsigned int rs_calc_weak_sum(void const *p, int len)
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{
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int i;
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unsigned s1, s2;
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unsigned char const *buf = (unsigned char const *) p;
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s1 = s2 = 0;
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for (i = 0; i < (len - 4); i += 4) {
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s2 += 4 * (s1 + buf[i]) + 3 * buf[i + 1] +
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2 * buf[i + 2] + buf[i + 3] + 10 * RS_CHAR_OFFSET;
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s1 += (buf[i + 0] + buf[i + 1] + buf[i + 2] + buf[i + 3] +
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4 * RS_CHAR_OFFSET);
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}
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for (; i < len; i++) {
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s1 += (buf[i] + RS_CHAR_OFFSET);
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s2 += s1;
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}
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return (s1 & 0xffff) + (s2 << 16);
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}
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/**
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* Calculate and store into SUM a strong MD4 checksum of the file
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* blocks seen so far.
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*
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* In plain rsync, the checksum is perturbed by a seed value. This is
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* used when retrying a failed transmission: we've discovered that the
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* hashes collided at some point, so we're going to try again with
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* different hashes to see if we can get it right. (Check tridge's
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* thesis for details and to see if that's correct.)
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*
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* Since we can't retry a web transaction I'm not sure if it's very
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* useful in rproxy.
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*/
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void rs_calc_strong_sum(void const *buf, size_t len, rs_strong_sum_t *sum)
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{
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rs_mdfour((unsigned char *) sum, buf, len);
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}
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