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/*
* Copyright (C) 2011 The Guava Authors
*
* 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.google.common.hash;
import static com.google.common.primitives.UnsignedBytes.toInt;
import java.io.Serializable;
import java.nio.ByteBuffer;
/**
* See http://smhasher.googlecode.com/svn/trunk/MurmurHash3.cpp
* MurmurHash3_x86_32
*
* @author aappleby@google.com (Austin Appleby)
* @author andreou@google.com (Dimitris Andreou)
*/
final class Murmur3_32HashFunction extends AbstractStreamingHashFunction implements Serializable {
private final int seed;
Murmur3_32HashFunction(int seed) {
this.seed = seed;
}
@Override public int bits() {
return 32;
}
@Override public Hasher newHasher() {
return new Murmur3_32Hasher(seed);
}
private static final class Murmur3_32Hasher extends AbstractStreamingHasher {
int h1;
int c1 = 0xcc9e2d51;
int c2 = 0x1b873593;
int len;
Murmur3_32Hasher(int seed) {
super(4);
h1 = seed;
}
@Override protected void process(ByteBuffer bb) {
int k1 = bb.getInt();
len += 4;
k1 *= c1;
k1 = Integer.rotateLeft(k1, 15);
k1 *= c2;
h1 ^= k1;
h1 = Integer.rotateLeft(h1, 13);
h1 = h1 * 5 + 0xe6546b64;
}
@Override protected void processRemaining(ByteBuffer bb) {
len += bb.remaining();
int k1 = 0;
switch (bb.remaining()) {
case 3:
k1 ^= toInt(bb.get(2)) << 16;
// fall through
case 2:
k1 ^= toInt(bb.get(1)) << 8;
// fall through
case 1:
k1 ^= toInt(bb.get(0));
// fall through
default:
k1 *= c1;
k1 = Integer.rotateLeft(k1, 15);
k1 *= c2;
h1 ^= k1;
}
}
@Override public HashCode makeHash() {
h1 ^= len;
h1 ^= h1 >>> 16;
h1 *= 0x85ebca6b;
h1 ^= h1 >>> 13;
h1 *= 0xc2b2ae35;
h1 ^= h1 >>> 16;
return HashCodes.fromInt(h1);
}
}
private static final long serialVersionUID = 0L;
}
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