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/*= -*- c-basic-offset: 4; indent-tabs-mode: nil; -*-
*
* rollsum -- the librsync rolling checksum
*
* Copyright (C) 2003 by Donovan Baarda <abo@minkirri.apana.org.au>
* based on work, Copyright (C) 2000, 2001 by Martin Pool <mbp@sourcefrog.net>
*
* 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 "rollsum.h"
#define DO1(buf,i) {s1 += buf[i]; s2 += s1;}
#define DO2(buf,i) DO1(buf,i); DO1(buf,i+1);
#define DO4(buf,i) DO2(buf,i); DO2(buf,i+2);
#define DO8(buf,i) DO4(buf,i); DO4(buf,i+4);
#define DO16(buf) DO8(buf,0); DO8(buf,8);
void RollsumUpdate(Rollsum *sum, const unsigned char *buf, size_t len)
{
/* ANSI C says no overflow for unsigned. zlib's adler32 goes to extra
effort to avoid overflow for its mod prime, which we don't have. */
size_t n = len;
uint_fast16_t s1 = sum->s1;
uint_fast16_t s2 = sum->s2;
while (n >= 16) {
DO16(buf);
buf += 16;
n -= 16;
}
while (n != 0) {
s1 += *buf++;
s2 += s1;
n--;
}
/* Increment s1 and s2 by the amounts added by the char offset. */
s1 += len * ROLLSUM_CHAR_OFFSET;
s2 += ((len * (len + 1)) / 2) * ROLLSUM_CHAR_OFFSET;
sum->count += len; /* Increment sum count. */
sum->s1 = s1;
sum->s2 = s2;
}