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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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