com.google.common.hash.SipHashFunction Maven / Gradle / Ivy
/*
* Copyright (C) 2012 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.
*/
/*
* SipHash-c-d was designed by Jean-Philippe Aumasson and Daniel J. Bernstein and is described in
* "SipHash: a fast short-input PRF" (available at https://131002.net/siphash/siphash.pdf).
*/
package com.google.common.hash;
import static com.google.common.base.Preconditions.checkArgument;
import java.io.Serializable;
import java.nio.ByteBuffer;
/**
* {@link HashFunction} implementation of SipHash-c-d.
*
* @author Kurt Alfred Kluever
* @author Jean-Philippe Aumasson
* @author Daniel J. Bernstein
*/
final class SipHashFunction extends AbstractHashFunction implements Serializable {
static final HashFunction SIP_HASH_24 =
new SipHashFunction(2, 4, 0x0706050403020100L, 0x0f0e0d0c0b0a0908L);
// The number of compression rounds.
private final int c;
// The number of finalization rounds.
private final int d;
// Two 64-bit keys (represent a single 128-bit key).
private final long k0;
private final long k1;
/**
* @param c the number of compression rounds (must be positive)
* @param d the number of finalization rounds (must be positive)
* @param k0 the first half of the key
* @param k1 the second half of the key
*/
SipHashFunction(int c, int d, long k0, long k1) {
checkArgument(
c > 0, "The number of SipRound iterations (c=%s) during Compression must be positive.", c);
checkArgument(
d > 0, "The number of SipRound iterations (d=%s) during Finalization must be positive.", d);
this.c = c;
this.d = d;
this.k0 = k0;
this.k1 = k1;
}
@Override
public int bits() {
return 64;
}
@Override
public Hasher newHasher() {
return new SipHasher(c, d, k0, k1);
}
// TODO(kak): Implement and benchmark the hashFoo() shortcuts.
@Override
public String toString() {
return "Hashing.sipHash" + c + "" + d + "(" + k0 + ", " + k1 + ")";
}
@Override
public boolean equals(Object object) {
if (object instanceof SipHashFunction) {
SipHashFunction other = (SipHashFunction) object;
return (c == other.c) && (d == other.d) && (k0 == other.k0) && (k1 == other.k1);
}
return false;
}
@Override
public int hashCode() {
return (int) (getClass().hashCode() ^ c ^ d ^ k0 ^ k1);
}
private static final class SipHasher extends AbstractStreamingHasher {
private static final int CHUNK_SIZE = 8;
// The number of compression rounds.
private final int c;
// The number of finalization rounds.
private final int d;
// Four 64-bit words of internal state.
// The initial state corresponds to the ASCII string "somepseudorandomlygeneratedbytes",
// big-endian encoded. There is nothing special about this value; the only requirement
// was some asymmetry so that the initial v0 and v1 differ from v2 and v3.
private long v0 = 0x736f6d6570736575L;
private long v1 = 0x646f72616e646f6dL;
private long v2 = 0x6c7967656e657261L;
private long v3 = 0x7465646279746573L;
// The number of bytes in the input.
private long b = 0;
// The final 64-bit chunk includes the last 0 through 7 bytes of m followed by null bytes
// and ending with a byte encoding the positive integer b mod 256.
private long finalM = 0;
SipHasher(int c, int d, long k0, long k1) {
super(CHUNK_SIZE);
this.c = c;
this.d = d;
this.v0 ^= k0;
this.v1 ^= k1;
this.v2 ^= k0;
this.v3 ^= k1;
}
@Override
protected void process(ByteBuffer buffer) {
b += CHUNK_SIZE;
processM(buffer.getLong());
}
@Override
protected void processRemaining(ByteBuffer buffer) {
b += buffer.remaining();
for (int i = 0; buffer.hasRemaining(); i += 8) {
finalM ^= (buffer.get() & 0xFFL) << i;
}
}
@Override
public HashCode makeHash() {
// End with a byte encoding the positive integer b mod 256.
finalM ^= b << 56;
processM(finalM);
// Finalization
v2 ^= 0xFFL;
sipRound(d);
return HashCode.fromLong(v0 ^ v1 ^ v2 ^ v3);
}
private void processM(long m) {
v3 ^= m;
sipRound(c);
v0 ^= m;
}
private void sipRound(int iterations) {
for (int i = 0; i < iterations; i++) {
v0 += v1;
v2 += v3;
v1 = Long.rotateLeft(v1, 13);
v3 = Long.rotateLeft(v3, 16);
v1 ^= v0;
v3 ^= v2;
v0 = Long.rotateLeft(v0, 32);
v2 += v1;
v0 += v3;
v1 = Long.rotateLeft(v1, 17);
v3 = Long.rotateLeft(v3, 21);
v1 ^= v2;
v3 ^= v0;
v2 = Long.rotateLeft(v2, 32);
}
}
}
private static final long serialVersionUID = 0L;
}