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/* -*- c-file-style: "bsd" -*-
* rproxy -- dynamic caching and delta update in HTTP
* $Id: rollsum.c,v 1.8 2000/08/06 12:50:36 mbp Exp $
*
* Copyright (C) 1999, 2000 by Martin Pool <mbp@humbug.org.au>
* Copyright (C) 1999 by Andrew Tridgell
*
* 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 "includes.h"
void
_hs_roll_reset(hs_rollsum_t * rollsum)
{
hs_bzero(rollsum, sizeof *rollsum);
}
int
_hs_stretch_sums(byte_t const *bytep, size_t full_block,
size_t short_block, hs_rollsum_t * rollsum)
{
/* Checksum calculations are signed */
int8_t const *p = (int8_t const *) bytep;
if (!rollsum->havesum) {
rollsum->weak_sum = _hs_calc_weak_sum(p, short_block);
_hs_trace("recalculate checksum: weak=%#x", rollsum->weak_sum);
rollsum->s1 = rollsum->weak_sum & 0xFFFF;
rollsum->s2 = rollsum->weak_sum >> 16;
} else {
/* Add into the checksum the value of the byte one block hence.
However, if that byte doesn't exist because we're approaching the
end of the file, don't add it. */
if (short_block == full_block) {
int pos = short_block - 1;
assert(pos >= 0);
rollsum->s1 += (p[pos] + CHAR_OFFSET);
rollsum->s2 += rollsum->s1;
}
rollsum->weak_sum = (rollsum->s1 & 0xffff) | (rollsum->s2 << 16);
}
rollsum->havesum = 1;
return 0;
}
/* One byte rolls off the checksum. */
int
_hs_trim_sums(byte_t const *bytep, hs_rollsum_t * rollsum, size_t short_block)
{
/* Checksum calculations are signed */
int8_t const *p = (int8_t const *) bytep;
rollsum->s1 -= *p + CHAR_OFFSET;
rollsum->s2 -= short_block * (*p + CHAR_OFFSET);
return 0;
}
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