1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
63
64
65
66
67
68
69
70
71
72
73
74
75
76
77
78
79
80
81
82
83
84
85
86
87
88
89
90
91
92
93
94
95
96
97
98
99
100
101
102
103
104
105
106
107
108
109
110
111
|
/*
* Copyright 2013 Rob Kendrick <rjek@netsurf-browser.org>
*
* This file is part of NetSurf, http://www.netsurf-browser.org/
*
* NetSurf is free software; you can redistribute it and/or modify
* it under the terms of the GNU General Public License as published by
* the Free Software Foundation; version 2 of the License.
*
* NetSurf 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 General Public License for more details.
*
* You should have received a copy of the GNU General Public License
* along with this program. If not, see <http://www.gnu.org/licenses/>.
*/
/**
* \file
* Trivial bloom filter
*/
#include <stdlib.h>
#include "utils/bloom.h"
#include "utils/utils.h"
/**
* Hash a string, returning a 32bit value. The hash algorithm used is
* Fowler Noll Vo - a very fast and simple hash, ideal for short strings.
* See http://en.wikipedia.org/wiki/Fowler_Noll_Vo_hash for more details.
*
* \param datum The string to hash.
* \param len size_t of data length.
* \return The calculated hash value for the datum.
*/
static inline uint32_t fnv(const char *datum, size_t len)
{
uint32_t z = 0x811c9dc5;
if (datum == NULL)
return 0;
while (len--) {
z *= 0x01000193;
z ^= *datum++;
}
return z;
}
struct bloom_filter {
size_t size;
uint32_t items;
uint8_t filter[FLEX_ARRAY_LEN_DECL];
};
struct bloom_filter *bloom_create(size_t size)
{
struct bloom_filter *r = calloc(sizeof(*r) + size, 1);
if (r == NULL)
return NULL;
r->size = size;
return r;
}
void bloom_destroy(struct bloom_filter *b)
{
free(b);
}
void bloom_insert_str(struct bloom_filter *b, const char *s, size_t z)
{
uint32_t hash = fnv(s, z);
bloom_insert_hash(b, hash);
}
void bloom_insert_hash(struct bloom_filter *b, uint32_t hash)
{
unsigned int index = hash % (b->size << 3);
unsigned int byte_index = index >> 3;
unsigned int bit_index = index & 7;
b->filter[byte_index] |= (1 << bit_index);
b->items++;
}
bool bloom_search_str(struct bloom_filter *b, const char *s, size_t z)
{
uint32_t hash = fnv(s, z);
return bloom_search_hash(b, hash);
}
bool bloom_search_hash(struct bloom_filter *b, uint32_t hash)
{
unsigned int index = hash % (b->size << 3);
unsigned int byte_index = index >> 3;
unsigned int bit_index = index & 7;
return (b->filter[byte_index] & (1 << bit_index)) != 0;
}
uint32_t bloom_items(struct bloom_filter *b)
{
return b->items;
}
|