/* * 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; }