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| 1 /* | 1 /* |
| 2 * Copyright (C) 2011 Apple Inc. All rights reserved. | 2 * Copyright (C) 2011 Apple Inc. All rights reserved. |
| 3 * | 3 * |
| 4 * Redistribution and use in source and binary forms, with or without | 4 * Redistribution and use in source and binary forms, with or without |
| 5 * modification, are permitted provided that the following conditions | 5 * modification, are permitted provided that the following conditions |
| 6 * are met: | 6 * are met: |
| 7 * 1. Redistributions of source code must retain the above copyright | 7 * 1. Redistributions of source code must retain the above copyright |
| 8 * notice, this list of conditions and the following disclaimer. | 8 * notice, this list of conditions and the following disclaimer. |
| 9 * 2. Redistributions in binary form must reproduce the above copyright | 9 * 2. Redistributions in binary form must reproduce the above copyright |
| 10 * notice, this list of conditions and the following disclaimer in the | 10 * notice, this list of conditions and the following disclaimer in the |
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| 25 | 25 |
| 26 #ifndef BloomFilter_h | 26 #ifndef BloomFilter_h |
| 27 #define BloomFilter_h | 27 #define BloomFilter_h |
| 28 | 28 |
| 29 #include "wtf/Allocator.h" | 29 #include "wtf/Allocator.h" |
| 30 #include "wtf/Compiler.h" | 30 #include "wtf/Compiler.h" |
| 31 #include "wtf/text/AtomicString.h" | 31 #include "wtf/text/AtomicString.h" |
| 32 | 32 |
| 33 namespace WTF { | 33 namespace WTF { |
| 34 | 34 |
| 35 // Counting bloom filter with k=2 and 8 bit counters. Uses 2^keyBits bytes of me
mory. | 35 // Counting bloom filter with k=2 and 8 bit counters. Uses 2^keyBits bytes of |
| 36 // False positive rate is approximately (1-e^(-2n/m))^2, where n is the number o
f unique | 36 // memory. False positive rate is approximately (1-e^(-2n/m))^2, where n is |
| 37 // keys and m is the table size (==2^keyBits). | 37 // the number of unique keys and m is the table size (==2^keyBits). |
| 38 template <unsigned keyBits> | 38 template <unsigned keyBits> |
| 39 class BloomFilter { | 39 class BloomFilter { |
| 40 USING_FAST_MALLOC(BloomFilter); | 40 USING_FAST_MALLOC(BloomFilter); |
| 41 | 41 |
| 42 public: | 42 public: |
| 43 static_assert(keyBits <= 16, "bloom filter key size check"); | 43 static_assert(keyBits <= 16, "bloom filter key size check"); |
| 44 | 44 |
| 45 static const size_t tableSize = 1 << keyBits; | 45 static const size_t tableSize = 1 << keyBits; |
| 46 static const unsigned keyMask = (1 << keyBits) - 1; | 46 static const unsigned keyMask = (1 << keyBits) - 1; |
| 47 static uint8_t maximumCount() { return std::numeric_limits<uint8_t>::max(); } | 47 static uint8_t maximumCount() { return std::numeric_limits<uint8_t>::max(); } |
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| 140 } | 140 } |
| 141 return true; | 141 return true; |
| 142 } | 142 } |
| 143 #endif | 143 #endif |
| 144 | 144 |
| 145 } // namespace WTF | 145 } // namespace WTF |
| 146 | 146 |
| 147 using WTF::BloomFilter; | 147 using WTF::BloomFilter; |
| 148 | 148 |
| 149 #endif | 149 #endif |
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