A murmur hash implemetation

Crypto.js

crypto = (function (){

    /**
     * JS Implementation of MurmurHash2
     *
     * @see http://github.com/garycourt/murmurhash-js
     *
     * @param {string} str ASCII only
     * @param {number} seed Positive integer only
     * @return {number} 32-bit positive integer hash
     */

    function murmurhash2_32_gc(str, seed) {
        var
            l = str.length,
            h = (seed || 0x9747b28c) ^ l,
            i = 0,
            k,
            a = 0xff,
            b = 0xffff,
            c = 0x5bd1e995;

        while (l >= 4) {
            k =
                ((str.charCodeAt(i) & a)) |
                ((str.charCodeAt(++i) & a) << 8) |
                ((str.charCodeAt(++i) & a) << 16) |
                ((str.charCodeAt(++i) & a) << 24);

            k = (((k & b) * c) + ((((k >>> 16) * c) & b) << 16));
            k ^= k >>> 24;
            k = (((k & b) * c) + ((((k >>> 16) * c) & b) << 16));

            h = (((h & b) * c) + ((((h >>> 16) * c) & b) << 16)) ^ k;

            l -= 4;
            ++i;
      }

        switch (l) {
            case 3: h ^= (str.charCodeAt(i + 2) & a) << 16;
            case 2: h ^= (str.charCodeAt(i + 1) & a) << 8;
            case 1: h ^= (str.charCodeAt(i) & a);
                    h = (((h & b) * c) + ((((h >>> 16) * c) & b) << 16));
        }

        h ^= h >>> 13;
        h = (((h & b) * c) + ((((h >>> 16) * c) & b) << 16));
        h ^= h >>> 15;

        return h >>> 0;
    }

    return {
        hash : murmurhash2_32_gc
    }

})();