io.takari.watchservice.XXHash Maven / Gradle / Ivy
package io.takari.watchservice;
/**
* Copyright 2014 Prasanth Jayachandran
*
* 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.
*/
/**
* XXHash 64-bit variant. https://code.google.com/p/xxhash/
* This implementation is adapted from
* https://github.com/airlift/slice/blob/master/src/main/java/io/airlift/slice/XxHash64.java
*/
public class XXHash {
private final static long PRIME64_1 = 0x9E3779B185EBCA87L;
private final static long PRIME64_2 = 0xC2B2AE3D27D4EB4FL;
private final static long PRIME64_3 = 0x165667B19E3779F9L;
private final static long PRIME64_4 = 0x85EBCA77C2b2AE63L;
private final static long PRIME64_5 = 0x27D4EB2F165667C5L;
private final static long DEFAULT_SEED = 0;
/**
* XXHash 64-bit variant.
*
* @param data - input byte array
* @return - hashcode
*/
public static long hash64(byte[] data) {
return hash64(data, data.length, DEFAULT_SEED);
}
/**
* XXHash 64-bit variant.
*
* @param data - input byte array
* @param length - length of array
* @param seed - seed. (default 0)
* @return - hashcode
*/
public static long hash64(byte[] data, int length, long seed) {
long hash;
int index = 0;
if (length >= 32) {
long v1 = seed + PRIME64_1 + PRIME64_2;
long v2 = seed + PRIME64_2;
long v3 = seed + 0;
long v4 = seed - PRIME64_1;
long limit = length - 32;
do {
long k1 = ((long) data[index] & 0xff)
| (((long) data[index + 1] & 0xff) << 8)
| (((long) data[index + 2] & 0xff) << 16)
| (((long) data[index + 3] & 0xff) << 24)
| (((long) data[index + 4] & 0xff) << 32)
| (((long) data[index + 5] & 0xff) << 40)
| (((long) data[index + 6] & 0xff) << 48)
| (((long) data[index + 7] & 0xff) << 56);
v1 = mix(v1, k1);
index += 8;
long k2 = ((long) data[index] & 0xff)
| (((long) data[index + 1] & 0xff) << 8)
| (((long) data[index + 2] & 0xff) << 16)
| (((long) data[index + 3] & 0xff) << 24)
| (((long) data[index + 4] & 0xff) << 32)
| (((long) data[index + 5] & 0xff) << 40)
| (((long) data[index + 6] & 0xff) << 48)
| (((long) data[index + 7] & 0xff) << 56);
v2 = mix(v2, k2);
index += 8;
long k3 = ((long) data[index] & 0xff)
| (((long) data[index + 1] & 0xff) << 8)
| (((long) data[index + 2] & 0xff) << 16)
| (((long) data[index + 3] & 0xff) << 24)
| (((long) data[index + 4] & 0xff) << 32)
| (((long) data[index + 5] & 0xff) << 40)
| (((long) data[index + 6] & 0xff) << 48)
| (((long) data[index + 7] & 0xff) << 56);
v3 = mix(v3, k3);
index += 8;
long k4 = ((long) data[index] & 0xff)
| (((long) data[index + 1] & 0xff) << 8)
| (((long) data[index + 2] & 0xff) << 16)
| (((long) data[index + 3] & 0xff) << 24)
| (((long) data[index + 4] & 0xff) << 32)
| (((long) data[index + 5] & 0xff) << 40)
| (((long) data[index + 6] & 0xff) << 48)
| (((long) data[index + 7] & 0xff) << 56);
v4 = mix(v4, k4);
index += 8;
} while (index <= limit);
hash = Long.rotateLeft(v1, 1) + Long.rotateLeft(v2, 7) + Long.rotateLeft(v3, 12) +
Long.rotateLeft(v4, 18);
hash = update(hash, v1);
hash = update(hash, v2);
hash = update(hash, v3);
hash = update(hash, v4);
} else {
hash = seed + PRIME64_5;
}
hash += length;
// tail
while (index <= length - 8) {
int tailStart = index;
long k = 0;
int remaining = length - index;
remaining = remaining > 8 ? 8 : remaining;
switch (remaining) {
case 8:
k |= (long) (data[tailStart + 7] & 0xff) << 56;
case 7:
k |= (long) (data[tailStart + 6] & 0xff) << 48;
case 6:
k |= (long) (data[tailStart + 5] & 0xff) << 40;
case 5:
k |= (long) (data[tailStart + 4] & 0xff) << 32;
case 4:
k |= (long) (data[tailStart + 3] & 0xff) << 24;
case 3:
k |= (long) (data[tailStart + 2] & 0xff) << 16;
case 2:
k |= (long) (data[tailStart + 1] & 0xff) << 8;
case 1:
k |= (long) (data[tailStart] & 0xff);
}
hash = updateTail(hash, k);
index += 8;
}
if (index <= length - 4) {
int tailStart = index;
int k = 0;
int remaining = length - index;
remaining = remaining > 4 ? 4 : remaining;
switch (remaining) {
case 4:
k |= (long) (data[tailStart + 3] & 0xff) << 24;
case 3:
k |= (long) (data[tailStart + 2] & 0xff) << 16;
case 2:
k |= (long) (data[tailStart + 1] & 0xff) << 8;
case 1:
k |= (long) (data[tailStart] & 0xff);
}
hash = updateTail(hash, k);
index += 4;
}
while (index < length) {
hash = updateTail(hash, data[index]);
index++;
}
hash = finalShuffle(hash);
return hash;
}
private static long mix(long current, long value) {
return Long.rotateLeft(current + value * PRIME64_2, 31) * PRIME64_1;
}
private static long update(long hash, long value) {
long temp = hash ^ mix(0, value);
return temp * PRIME64_1 + PRIME64_4;
}
private static long updateTail(long hash, long value) {
long temp = hash ^ mix(0, value);
return Long.rotateLeft(temp, 27) * PRIME64_1 + PRIME64_4;
}
private static long updateTail(long hash, int value) {
long unsigned = value & 0xFFFFFFFFL;
long temp = hash ^ (unsigned * PRIME64_1);
return Long.rotateLeft(temp, 23) * PRIME64_2 + PRIME64_3;
}
private static long updateTail(long hash, byte value) {
int unsigned = value & 0xFF;
long temp = hash ^ (unsigned * PRIME64_5);
return Long.rotateLeft(temp, 11) * PRIME64_1;
}
private static long finalShuffle(long hash) {
hash ^= hash >>> 33;
hash *= PRIME64_2;
hash ^= hash >>> 29;
hash *= PRIME64_3;
hash ^= hash >>> 32;
return hash;
}
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