| /* |
| * Copyright 2000-2012 JetBrains s.r.o. |
| * |
| * Licensed under the Apache License, Version 2.0 (the "License"); |
| * you may not use this file except in compliance with the License. |
| * You may obtain a copy of the License at |
| * |
| * http://www.apache.org/licenses/LICENSE-2.0 |
| * |
| * Unless required by applicable law or agreed to in writing, software |
| * distributed under the License is distributed on an "AS IS" BASIS, |
| * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. |
| * See the License for the specific language governing permissions and |
| * limitations under the License. |
| */ |
| package com.intellij.util; |
| |
| public class BloomFilterBase { |
| private final int myHashFunctionCount; |
| private final int myBitsCount; |
| private final long[] myElementsSet; |
| private static final int BITS_PER_ELEMENT = 6; |
| |
| protected BloomFilterBase(int _maxElementCount, double probability) { |
| int bitsPerElementFactor = (int)Math.ceil(-Math.log(probability) / (Math.log(2) * Math.log(2))); |
| myHashFunctionCount = (int)Math.ceil(bitsPerElementFactor * Math.log(2)); |
| |
| int bitsCount = _maxElementCount * bitsPerElementFactor; |
| |
| if ((bitsCount & 1) == 0) ++bitsCount; |
| while(!isPrime(bitsCount)) bitsCount += 2; |
| myBitsCount = bitsCount; |
| myElementsSet = new long[(bitsCount >> BITS_PER_ELEMENT) + 1]; |
| } |
| |
| private static boolean isPrime(int bits) { |
| if ((bits & 1) == 0 || bits % 3 == 0) return false; |
| int sqrt = (int)Math.sqrt(bits); |
| for(int i = 6; i <= sqrt; i += 6) { |
| if (bits % (i - 1) == 0 || bits % (i + 1) == 0) return false; |
| } |
| return true; |
| } |
| |
| protected final void addIt(int prime, int prime2) { |
| for(int i = 0; i < myHashFunctionCount; ++i) { |
| int abs = Math.abs(i * prime + prime2 * (myHashFunctionCount - i)) % myBitsCount; |
| myElementsSet[abs >> BITS_PER_ELEMENT] |= (1L << abs); |
| } |
| } |
| |
| protected final boolean maybeContains(int prime, int prime2) { |
| for(int i = 0; i < myHashFunctionCount; ++i) { |
| int abs = Math.abs(i * prime + prime2 * (myHashFunctionCount - i)) % myBitsCount; |
| if ((myElementsSet[abs >> BITS_PER_ELEMENT] & (1L << abs)) == 0) return false; |
| } |
| |
| return true; |
| } |
| } |