| /* |
| * Copyright (C) 2011 Apple Inc. All rights reserved. |
| * |
| * Redistribution and use in source and binary forms, with or without |
| * modification, are permitted provided that the following conditions |
| * are met: |
| * 1. Redistributions of source code must retain the above copyright |
| * notice, this list of conditions and the following disclaimer. |
| * 2. Redistributions in binary form must reproduce the above copyright |
| * notice, this list of conditions and the following disclaimer in the |
| * documentation and/or other materials provided with the distribution. |
| * |
| * THIS SOFTWARE IS PROVIDED BY APPLE INC. AND ITS CONTRIBUTORS ``AS IS'' |
| * AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, |
| * THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR |
| * PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL APPLE INC. OR ITS CONTRIBUTORS |
| * BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR |
| * CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF |
| * SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS |
| * INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN |
| * CONTRACT, STRICT LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) |
| * ARISING IN ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF |
| * THE POSSIBILITY OF SUCH DAMAGE. |
| */ |
| |
| #ifndef BloomFilter_h |
| #define BloomFilter_h |
| |
| #include <wtf/AlwaysInline.h> |
| #include <wtf/text/AtomicString.h> |
| |
| namespace WTF { |
| |
| // Counting bloom filter with k=2 and 8 bit counters. Uses 2^keyBits bytes of memory. |
| // False positive rate is approximately (1-e^(-2n/m))^2, where n is the number of unique |
| // keys and m is the table size (==2^keyBits). |
| template <unsigned keyBits> |
| class BloomFilter { |
| public: |
| COMPILE_ASSERT(keyBits <= 16, bloom_filter_key_size); |
| |
| static const size_t tableSize = 1 << keyBits; |
| static const unsigned keyMask = (1 << keyBits) - 1; |
| static uint8_t maximumCount() { return std::numeric_limits<uint8_t>::max(); } |
| |
| BloomFilter() { clear(); } |
| |
| void add(unsigned hash); |
| void remove(unsigned hash); |
| |
| // The filter may give false positives (claim it may contain a key it doesn't) |
| // but never false negatives (claim it doesn't contain a key it does). |
| bool mayContain(unsigned hash) const { return firstSlot(hash) && secondSlot(hash); } |
| |
| // The filter must be cleared before reuse even if all keys are removed. |
| // Otherwise overflowed keys will stick around. |
| void clear(); |
| |
| void add(const AtomicString& string) { add(string.impl()->existingHash()); } |
| void add(const String& string) { add(string.impl()->hash()); } |
| void remove(const AtomicString& string) { remove(string.impl()->existingHash()); } |
| void remove(const String& string) { remove(string.impl()->hash()); } |
| |
| bool mayContain(const AtomicString& string) const { return mayContain(string.impl()->existingHash()); } |
| bool mayContain(const String& string) const { return mayContain(string.impl()->hash()); } |
| |
| #if !ASSERT_DISABLED |
| // Slow. |
| bool likelyEmpty() const; |
| bool isClear() const; |
| #endif |
| |
| private: |
| uint8_t& firstSlot(unsigned hash) { return m_table[hash & keyMask]; } |
| uint8_t& secondSlot(unsigned hash) { return m_table[(hash >> 16) & keyMask]; } |
| const uint8_t& firstSlot(unsigned hash) const { return m_table[hash & keyMask]; } |
| const uint8_t& secondSlot(unsigned hash) const { return m_table[(hash >> 16) & keyMask]; } |
| |
| uint8_t m_table[tableSize]; |
| }; |
| |
| template <unsigned keyBits> |
| inline void BloomFilter<keyBits>::add(unsigned hash) |
| { |
| uint8_t& first = firstSlot(hash); |
| uint8_t& second = secondSlot(hash); |
| if (LIKELY(first < maximumCount())) |
| ++first; |
| if (LIKELY(second < maximumCount())) |
| ++second; |
| } |
| |
| template <unsigned keyBits> |
| inline void BloomFilter<keyBits>::remove(unsigned hash) |
| { |
| uint8_t& first = firstSlot(hash); |
| uint8_t& second = secondSlot(hash); |
| ASSERT(first); |
| ASSERT(second); |
| // In case of an overflow, the slot sticks in the table until clear(). |
| if (LIKELY(first < maximumCount())) |
| --first; |
| if (LIKELY(second < maximumCount())) |
| --second; |
| } |
| |
| template <unsigned keyBits> |
| inline void BloomFilter<keyBits>::clear() |
| { |
| memset(m_table, 0, tableSize); |
| } |
| |
| #if !ASSERT_DISABLED |
| template <unsigned keyBits> |
| bool BloomFilter<keyBits>::likelyEmpty() const |
| { |
| for (size_t n = 0; n < tableSize; ++n) { |
| if (m_table[n] && m_table[n] != maximumCount()) |
| return false; |
| } |
| return true; |
| } |
| |
| template <unsigned keyBits> |
| bool BloomFilter<keyBits>::isClear() const |
| { |
| for (size_t n = 0; n < tableSize; ++n) { |
| if (m_table[n]) |
| return false; |
| } |
| return true; |
| } |
| #endif |
| |
| } |
| |
| using WTF::BloomFilter; |
| |
| #endif |