/*
* This code is public domain.
*
* The MurmurHash3 algorithm was created by Austin Appleby and put into the public domain. See http://code.google.com/p/smhasher/
*
* This java port was authored by
* Yonik Seeley and was placed into the public domain per https://github.com/yonik/java_util/blob/master/src/util/hash/MurmurHash3.java.
*/
package org.apache.mahout.math;
/**
* <p>
* This produces exactly the same hash values as the final C++
* version of MurmurHash3 and is thus suitable for producing the same hash values across
* platforms.
* <p>
* The 32 bit x86 version of this hash should be the fastest variant for relatively short keys like ids.
* <p>
* Note - The x86 and x64 versions do _not_ produce the same results, as the
* algorithms are optimized for their respective platforms.
* <p>
* See also http://github.com/yonik/java_util for future updates to this file.
*/
public class MurmurHash3 {
private MurmurHash3() {
}
/** Returns the MurmurHash3_x86_32 hash. */
public static int murmurhash3_x86_32(byte[] data, int offset, int len, int seed) {
int c1 = 0xcc9e2d51;
int c2 = 0x1b873593;
int h1 = seed;
int roundedEnd = offset + (len & 0xfffffffc); // round down to 4 byte block
for (int i=offset; i<roundedEnd; i+=4) {
// little endian load order
int k1 = (data[i] & 0xff) | ((data[i+1] & 0xff) << 8) | ((data[i+2] & 0xff) << 16) | (data[i+3] << 24);
k1 *= c1;
k1 = (k1 << 15) | (k1 >>> 17); // ROTL32(k1,15);
k1 *= c2;
h1 ^= k1;
h1 = (h1 << 13) | (h1 >>> 19); // ROTL32(h1,13);
h1 = h1*5+0xe6546b64;
}
// tail
int k1 = 0;
switch(len & 0x03) {
case 3:
k1 = (data[roundedEnd + 2] & 0xff) << 16;
// fallthrough
case 2:
k1 |= (data[roundedEnd + 1] & 0xff) << 8;
// fallthrough
case 1:
k1 |= data[roundedEnd] & 0xff;
k1 *= c1;
k1 = (k1 << 15) | (k1 >>> 17); // ROTL32(k1,15);
k1 *= c2;
h1 ^= k1;
}
// finalization
h1 ^= len;
// fmix(h1);
h1 ^= h1 >>> 16;
h1 *= 0x85ebca6b;
h1 ^= h1 >>> 13;
h1 *= 0xc2b2ae35;
h1 ^= h1 >>> 16;
return h1;
}
}