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/*= -*- c-file-style: "bsd" -*-
* rproxy -- dynamic caching and delta update in HTTP
* $Id: search.c,v 1.20 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.
*/
/*
* This file contains code for searching the sumset for matching
* values.
*/
/*
* TODO: The common case is that the next block in both streams
* match. Can we make that a bit faster at all? We'd need to perhaps
* add a link forward between blocks in the sum_struct corresponding
* to the order they're found in the input; then before doing a search
* we can just check that pointer.
*/
#include "includes.h"
#include "search.h"
#include "sum_p.h"
#define TABLESIZE (1<<16)
#define NULL_TAG (-1)
#define gettag2(s1,s2) (((s1) + (s2)) & 0xFFFF)
#define gettag(sum) gettag2((sum)&0xFFFF,(sum)>>16)
static int
_hs_compare_targets(struct target const *t1, struct target const *t2)
{
return ((int) t1->t - (int) t2->t);
}
int
_hs_build_hash_table(hs_sumset_t * sums)
{
int i;
sums->tag_table = calloc(TABLESIZE, sizeof sums->tag_table[0]);
if (sums->count > 0) {
sums->targets = calloc(sums->count, sizeof(struct target));
for (i = 0; i < sums->count; i++) {
sums->targets[i].i = i;
sums->targets[i].t = gettag(sums->block_sums[i].weak_sum);
}
/* FIXME: Perhaps if this operating system has comparison_fn_t
* like GNU, then use it in the cast. But really does anyone
* care? */
qsort(sums->targets, sums->count,
sizeof(sums->targets[0]),
(int (*)(const void *, const void *)) _hs_compare_targets);
}
for (i = 0; i < TABLESIZE; i++)
sums->tag_table[i] = NULL_TAG;
for (i = sums->count - 1; i >= 0; i--) {
sums->tag_table[sums->targets[i].t] = i;
}
return 0;
}
/*
* See if there is a match for the specified block INBUF..BLOCK_LEN in
* the checksum set, using precalculated WEAK_SUM.
*
* If we don't find a match on the weak checksum, then we just give
* up. If we do find a weak match, then we proceed to calculate the
* strong checksum for the current block, and see if it will match
* anything.
*/
int
_hs_search_for_block(hs_weak_sum_t weak_sum,
byte_t const *inbuf, size_t block_len,
hs_sumset_t const *sums, hs_stats_t * stats,
off_t * match_where)
{
int hash_tag = gettag(weak_sum);
int j = sums->tag_table[hash_tag];
byte_t strong_sum[DEFAULT_SUM_LENGTH];
int got_strong = 0;
if (j == NULL_TAG) {
return 0;
}
for (; j < sums->count && sums->targets[j].t == hash_tag; j++) {
int i = sums->targets[j].i;
int token;
if (weak_sum != sums->block_sums[i].weak_sum)
continue;
/* also make sure the two blocks are the same length */
/* l = MIN(s->n,len-offset); */
/* if (l != s->block_sums[i].len) continue; */
/* if (!done_csum2) { */
/* map = (schar *)map_ptr(buf,offset,l); */
/* get_checksum2((char *)map,l,sum2); */
/* done_csum2 = 1; */
/* } */
token = sums->block_sums[i].i;
_hs_trace("found weak match for %08x in token %d", weak_sum, token);
if (!got_strong) {
_hs_calc_strong_sum(inbuf, block_len, strong_sum,
DEFAULT_SUM_LENGTH);
got_strong = 1;
}
/* FIXME: Use correct dynamic sum length! */
if (memcmp(strong_sum, sums->block_sums[i].strong_sum,
DEFAULT_SUM_LENGTH) == 0) {
/* XXX: This is a remnant of rsync: token number 1 is the * block
* at offset 0. It would be good to clear this * up. */
*match_where = (token - 1) * sums->block_len;
return 1;
} else {
_hs_trace("this was a false positive, the strong sums "
"don't match");
stats->false_matches++;
}
}
return 0;
}
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