@emartech/faye-redis-sharded/lib/sharding/algorithms/murmur-hash3.js

Redis backend engine for Faye with support for sharding

/**
 * JS Implementation of MurmurHash3 (r136) (as of May 20, 2011)
 *
 * @author <a href="mailto:gary.court@gmail.com">Gary Court</a>
 * @see http://github.com/garycourt/murmurhash-js
 * @author <a href="mailto:aappleby@gmail.com">Austin Appleby</a>
 * @see http://sites.google.com/site/murmurhash/
 *
 */

function MurmurHash3(seed) {
	this.seed = seed || 0xc58f1a7b;
}

MurmurHash3.prototype.getHash = function (key) {
	var remainder = key.length & 3; // key.length % 4
	var bytes = key.length - remainder;
	var h1 = this.seed;
	var c1 = 0xcc9e2d51;
	var c2 = 0x1b873593;
	var i = 0;

	var c1_l = c1 & 0xffff;
	var c1_h = c1 & 0xffff0000;
	var c2_l = c2 & 0xffff;
	var c2_h = c2 & 0xffff0000;
	var k1;

	while (i < bytes) {
		k1 = ((key.charCodeAt(i++) & 0xff)      ) |
			((key.charCodeAt(i++) & 0xff) << 8 ) |
			((key.charCodeAt(i++) & 0xff) << 16) |
			((key.charCodeAt(i++) & 0xff) << 24);

		k1 = (k1 * c1_l + (k1 & 0xffff) * c1_h) & 0xffffffff; // note that javascript precision is 2^53
		k1 = (k1 << 15) | (k1 >>> 17);
		k1 = (k1 * c2_l + (k1 & 0xffff) * c2_h) & 0xffffffff;

		h1 ^= k1;
		h1 = (h1 << 13) | (h1 >>> 19);
		h1 = (h1 * 5 + 0xe6546b64) & 0xffffffff;
	}

	k1 = 0;

	switch (remainder) {
		case 3:
			k1 ^= (key.charCodeAt(i + 2) & 0xff) << 16;
		case 2:
			k1 ^= (key.charCodeAt(i + 1) & 0xff) << 8;
		case 1:
			k1 ^= (key.charCodeAt(i) & 0xff);

			k1 = (k1 * c1_l + (k1 & 0xffff) * c1_h) & 0xffffffff;
			k1 = (k1 << 16) | (k1 >>> 16);
			k1 = (k1 * c2_l + (k1 & 0xffff) * c2_h) & 0xffffffff;
			h1 ^= k1;
	}

	h1 ^= key.length;

	h1 ^= h1 >>> 16;
	h1 = (h1 * 0xca6b + (h1 & 0xffff) * 0x85eb0000) & 0xffffffff;
	h1 ^= h1 >>> 13;
	h1 = (h1 * 0xae35 + (h1 & 0xffff) * 0xc2b20000) & 0xffffffff;
	h1 ^= h1 >>> 16;

	return h1 >>> 0;
};

module.exports = MurmurHash3;