package org.jruby.util;

public class MurmurHash {

// Based on Murmurhash 2.0 Java port at http://dmy999.com/article/50/murmurhash-2-java-port

// 2011-12-05: Modified by Hiroshi Nakamura <nahi@ruby-lang.org>

// - signature change to use offset

// hash(byte[] data, int seed) to hash(byte[] src, int offset, int length, int seed)

// - extract 'm' and 'r' as murmurhash2.0 constants

// Ported by Derek Young from the C version (specifically the endian-neutral

// version) from:

// http://murmurhash.googlepages.com/

//

// released to the public domain - dmy999@gmail.com

// 'm' and 'r' are mixing constants generated offline.

// They're not really 'magic', they just happen to work well.

private static final int MURMUR2_MAGIC = 0x5bd1e995;

// CRuby 1.9 uses 16 but original C++ implementation uses 24 with above Magic.

private static final int MURMUR2_R = 24;

@SuppressWarnings("fallthrough")

public static int hash32(byte[] src, int offset, int length, int seed) {

// Initialize the hash to a 'random' value

int h = seed ^ length;

int i = offset;

int len = length;

while (len >= 4) {

int k = src[i + 0] & 0xFF;

k |= (src[i + 1] & 0xFF) << 8;

k |= (src[i + 2] & 0xFF) << 16;

k |= (src[i + 3] & 0xFF) << 24;

k *= MURMUR2_MAGIC;

k ^= k >>> MURMUR2_R;

k *= MURMUR2_MAGIC;

h *= MURMUR2_MAGIC;

h ^= k;

i += 4;

len -= 4;

}

switch (len) {

case 3:

h ^= (src[i + 2] & 0xFF) << 16;

case 2:

h ^= (src[i + 1] & 0xFF) << 8;

case 1:

h ^= (src[i + 0] & 0xFF);

h *= MURMUR2_MAGIC;

}

h ^= h >>> 13;

h *= MURMUR2_MAGIC;

h ^= h >>> 15;

return h;

}

}