112 lines
2.5 KiB
C
112 lines
2.5 KiB
C
/*
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* Copyright 2013 Rob Kendrick <rjek@netsurf-browser.org>
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*
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* This file is part of NetSurf, http://www.netsurf-browser.org/
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*
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* NetSurf is free software; you can redistribute it and/or modify
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* it under the terms of the GNU General Public License as published by
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* the Free Software Foundation; version 2 of the License.
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*
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* NetSurf is distributed in the hope that it will be useful,
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* but WITHOUT ANY WARRANTY; without even the implied warranty of
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* MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
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* GNU General Public License for more details.
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*
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* You should have received a copy of the GNU General Public License
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* along with this program. If not, see <http://www.gnu.org/licenses/>.
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*/
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/**
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* \file
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* Trivial bloom filter
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*/
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#include <stdlib.h>
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#include "utils/bloom.h"
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#include "utils/utils.h"
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/**
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* Hash a string, returning a 32bit value. The hash algorithm used is
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* Fowler Noll Vo - a very fast and simple hash, ideal for short strings.
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* See http://en.wikipedia.org/wiki/Fowler_Noll_Vo_hash for more details.
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*
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* \param datum The string to hash.
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* \param len size_t of data length.
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* \return The calculated hash value for the datum.
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*/
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static inline uint32_t fnv(const char *datum, size_t len)
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{
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uint32_t z = 0x811c9dc5;
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if (datum == NULL)
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return 0;
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while (len--) {
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z *= 0x01000193;
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z ^= *datum++;
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}
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return z;
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}
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struct bloom_filter {
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size_t size;
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uint32_t items;
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uint8_t filter[FLEX_ARRAY_LEN_DECL];
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};
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struct bloom_filter *bloom_create(size_t size)
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{
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struct bloom_filter *r = calloc(sizeof(*r) + size, 1);
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if (r == NULL)
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return NULL;
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r->size = size;
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return r;
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}
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void bloom_destroy(struct bloom_filter *b)
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{
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free(b);
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}
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void bloom_insert_str(struct bloom_filter *b, const char *s, size_t z)
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{
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uint32_t hash = fnv(s, z);
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bloom_insert_hash(b, hash);
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}
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void bloom_insert_hash(struct bloom_filter *b, uint32_t hash)
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{
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unsigned int index = hash % (b->size << 3);
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unsigned int byte_index = index >> 3;
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unsigned int bit_index = index & 7;
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b->filter[byte_index] |= (1 << bit_index);
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b->items++;
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}
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bool bloom_search_str(struct bloom_filter *b, const char *s, size_t z)
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{
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uint32_t hash = fnv(s, z);
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return bloom_search_hash(b, hash);
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}
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bool bloom_search_hash(struct bloom_filter *b, uint32_t hash)
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{
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unsigned int index = hash % (b->size << 3);
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unsigned int byte_index = index >> 3;
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unsigned int bit_index = index & 7;
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return (b->filter[byte_index] & (1 << bit_index)) != 0;
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}
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uint32_t bloom_items(struct bloom_filter *b)
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{
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return b->items;
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}
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