com.google.common.hash.FarmHashFingerprint64 Maven / Gradle / Ivy
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This artifact provides a single jar that contains all classes required to use remote EJB and JMS, including
all dependencies. It is intended for use by those not using maven, maven users should just import the EJB and
JMS BOM's instead (shaded JAR's cause lots of problems with maven, as it is very easy to inadvertently end up
with different versions on classes on the class path).
/*
* Copyright (C) 2015 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.base.Preconditions.checkPositionIndexes;
import static com.google.common.hash.LittleEndianByteArray.load32;
import static com.google.common.hash.LittleEndianByteArray.load64;
import static java.lang.Long.rotateRight;
import com.google.common.annotations.VisibleForTesting;
/**
* Implementation of FarmHash Fingerprint64, an open-source fingerprinting algorithm for strings.
*
* Its speed is comparable to CityHash64, and its quality of hashing is at least as good.
*
*
Note to maintainers: This implementation relies on signed arithmetic being bit-wise equivalent
* to unsigned arithmetic in all cases except:
*
*
* - comparisons (signed values can be negative)
*
- division (avoided here)
*
- shifting (right shift must be unsigned)
*
*
* @author Kyle Maddison
* @author Geoff Pike
*/
@ElementTypesAreNonnullByDefault
final class FarmHashFingerprint64 extends AbstractNonStreamingHashFunction {
static final HashFunction FARMHASH_FINGERPRINT_64 = new FarmHashFingerprint64();
// Some primes between 2^63 and 2^64 for various uses.
private static final long K0 = 0xc3a5c85c97cb3127L;
private static final long K1 = 0xb492b66fbe98f273L;
private static final long K2 = 0x9ae16a3b2f90404fL;
@Override
public HashCode hashBytes(byte[] input, int off, int len) {
checkPositionIndexes(off, off + len, input.length);
return HashCode.fromLong(fingerprint(input, off, len));
}
@Override
public int bits() {
return 64;
}
@Override
public String toString() {
return "Hashing.farmHashFingerprint64()";
}
// End of public functions.
@VisibleForTesting
static long fingerprint(byte[] bytes, int offset, int length) {
if (length <= 32) {
if (length <= 16) {
return hashLength0to16(bytes, offset, length);
} else {
return hashLength17to32(bytes, offset, length);
}
} else if (length <= 64) {
return hashLength33To64(bytes, offset, length);
} else {
return hashLength65Plus(bytes, offset, length);
}
}
private static long shiftMix(long val) {
return val ^ (val >>> 47);
}
private static long hashLength16(long u, long v, long mul) {
long a = (u ^ v) * mul;
a ^= (a >>> 47);
long b = (v ^ a) * mul;
b ^= (b >>> 47);
b *= mul;
return b;
}
/**
* Computes intermediate hash of 32 bytes of byte array from the given offset. Results are
* returned in the output array because when we last measured, this was 12% faster than allocating
* new arrays every time.
*/
private static void weakHashLength32WithSeeds(
byte[] bytes, int offset, long seedA, long seedB, long[] output) {
long part1 = load64(bytes, offset);
long part2 = load64(bytes, offset + 8);
long part3 = load64(bytes, offset + 16);
long part4 = load64(bytes, offset + 24);
seedA += part1;
seedB = rotateRight(seedB + seedA + part4, 21);
long c = seedA;
seedA += part2;
seedA += part3;
seedB += rotateRight(seedA, 44);
output[0] = seedA + part4;
output[1] = seedB + c;
}
private static long hashLength0to16(byte[] bytes, int offset, int length) {
if (length >= 8) {
long mul = K2 + length * 2;
long a = load64(bytes, offset) + K2;
long b = load64(bytes, offset + length - 8);
long c = rotateRight(b, 37) * mul + a;
long d = (rotateRight(a, 25) + b) * mul;
return hashLength16(c, d, mul);
}
if (length >= 4) {
long mul = K2 + length * 2;
long a = load32(bytes, offset) & 0xFFFFFFFFL;
return hashLength16(length + (a << 3), load32(bytes, offset + length - 4) & 0xFFFFFFFFL, mul);
}
if (length > 0) {
byte a = bytes[offset];
byte b = bytes[offset + (length >> 1)];
byte c = bytes[offset + (length - 1)];
int y = (a & 0xFF) + ((b & 0xFF) << 8);
int z = length + ((c & 0xFF) << 2);
return shiftMix(y * K2 ^ z * K0) * K2;
}
return K2;
}
private static long hashLength17to32(byte[] bytes, int offset, int length) {
long mul = K2 + length * 2;
long a = load64(bytes, offset) * K1;
long b = load64(bytes, offset + 8);
long c = load64(bytes, offset + length - 8) * mul;
long d = load64(bytes, offset + length - 16) * K2;
return hashLength16(
rotateRight(a + b, 43) + rotateRight(c, 30) + d, a + rotateRight(b + K2, 18) + c, mul);
}
private static long hashLength33To64(byte[] bytes, int offset, int length) {
long mul = K2 + length * 2;
long a = load64(bytes, offset) * K2;
long b = load64(bytes, offset + 8);
long c = load64(bytes, offset + length - 8) * mul;
long d = load64(bytes, offset + length - 16) * K2;
long y = rotateRight(a + b, 43) + rotateRight(c, 30) + d;
long z = hashLength16(y, a + rotateRight(b + K2, 18) + c, mul);
long e = load64(bytes, offset + 16) * mul;
long f = load64(bytes, offset + 24);
long g = (y + load64(bytes, offset + length - 32)) * mul;
long h = (z + load64(bytes, offset + length - 24)) * mul;
return hashLength16(
rotateRight(e + f, 43) + rotateRight(g, 30) + h, e + rotateRight(f + a, 18) + g, mul);
}
/*
* Compute an 8-byte hash of a byte array of length greater than 64 bytes.
*/
private static long hashLength65Plus(byte[] bytes, int offset, int length) {
int seed = 81;
// For strings over 64 bytes we loop. Internal state consists of 56 bytes: v, w, x, y, and z.
long x = seed;
@SuppressWarnings("ConstantOverflow")
long y = seed * K1 + 113;
long z = shiftMix(y * K2 + 113) * K2;
long[] v = new long[2];
long[] w = new long[2];
x = x * K2 + load64(bytes, offset);
// Set end so that after the loop we have 1 to 64 bytes left to process.
int end = offset + ((length - 1) / 64) * 64;
int last64offset = end + ((length - 1) & 63) - 63;
do {
x = rotateRight(x + y + v[0] + load64(bytes, offset + 8), 37) * K1;
y = rotateRight(y + v[1] + load64(bytes, offset + 48), 42) * K1;
x ^= w[1];
y += v[0] + load64(bytes, offset + 40);
z = rotateRight(z + w[0], 33) * K1;
weakHashLength32WithSeeds(bytes, offset, v[1] * K1, x + w[0], v);
weakHashLength32WithSeeds(bytes, offset + 32, z + w[1], y + load64(bytes, offset + 16), w);
long tmp = x;
x = z;
z = tmp;
offset += 64;
} while (offset != end);
long mul = K1 + ((z & 0xFF) << 1);
// Operate on the last 64 bytes of input.
offset = last64offset;
w[0] += ((length - 1) & 63);
v[0] += w[0];
w[0] += v[0];
x = rotateRight(x + y + v[0] + load64(bytes, offset + 8), 37) * mul;
y = rotateRight(y + v[1] + load64(bytes, offset + 48), 42) * mul;
x ^= w[1] * 9;
y += v[0] * 9 + load64(bytes, offset + 40);
z = rotateRight(z + w[0], 33) * mul;
weakHashLength32WithSeeds(bytes, offset, v[1] * mul, x + w[0], v);
weakHashLength32WithSeeds(bytes, offset + 32, z + w[1], y + load64(bytes, offset + 16), w);
return hashLength16(
hashLength16(v[0], w[0], mul) + shiftMix(y) * K0 + x,
hashLength16(v[1], w[1], mul) + z,
mul);
}
}