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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.
*/
/** \file rollsum.h
* The Rollsum class implementation of the original rsync rollsum. */
#ifndef ROLLSUM_H
# define ROLLSUM_H
# include <stddef.h>
# include <stdint.h>
/* We should make this something other than zero to improve the checksum
algorithm: tridge suggests a prime number. */
# define ROLLSUM_CHAR_OFFSET 31
/** The Rollsum state type. */
typedef struct Rollsum {
size_t count; /**< count of bytes included in sum */
uint_fast16_t s1; /**< s1 part of sum */
uint_fast16_t s2; /**< s2 part of sum */
} Rollsum;
void RollsumUpdate(Rollsum *sum, const unsigned char *buf, size_t len);
/* static inline implementations of simple routines */
static inline void RollsumInit(Rollsum *sum)
{
sum->count = sum->s1 = sum->s2 = 0;
}
static inline void RollsumRotate(Rollsum *sum, unsigned char out,
unsigned char in)
{
sum->s1 += in - out;
sum->s2 += sum->s1 - (uint_fast16_t)sum->count * (out + ROLLSUM_CHAR_OFFSET);
}
static inline void RollsumRollin(Rollsum *sum, unsigned char in)
{
sum->s1 += in + ROLLSUM_CHAR_OFFSET;
sum->s2 += sum->s1;
sum->count++;
}
static inline void RollsumRollout(Rollsum *sum, unsigned char out)
{
sum->s1 -= out + ROLLSUM_CHAR_OFFSET;
sum->s2 -= (uint_fast16_t)sum->count * (out + ROLLSUM_CHAR_OFFSET);
sum->count--;
}
static inline uint32_t RollsumDigest(Rollsum *sum)
{
return ((uint32_t)sum->s2 << 16) | ((uint32_t)sum->s1 & 0xffff);
}
#endif /* !ROLLSUM_H */
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