Murmur hash in JavaScript

gistfile1.js

function murmurhash(key, seed) {
    var remainder, bytes, h1, h1b, c1, c1b, c2, c2b, k1, i;

    remainder = key.length & 3; // key.length % 4
    bytes = key.length - remainder;
    h1 = seed;
    c1 = 0xcc9e2d51;
    c2 = 0x1b873593;
    i = 0;

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

        k1 = ((((k1 & 0xffff) * c1) + ((((k1 >>> 16) * c1) & 0xffff) << 16))) & 0xffffffff;
        k1 = (k1 << 15) | (k1 >>> 17);
        k1 = ((((k1 & 0xffff) * c2) + ((((k1 >>> 16) * c2) & 0xffff) << 16))) & 0xffffffff;

        h1 ^= k1;
        h1 = (h1 << 13) | (h1 >>> 19);
        h1b = ((((h1 & 0xffff) * 5) + ((((h1 >>> 16) * 5) & 0xffff) << 16))) & 0xffffffff;
        h1 = (((h1b & 0xffff) + 0x6b64) + ((((h1b >>> 16) + 0xe654) & 0xffff) << 16));
    }

    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 & 0xffff) * c1) + ((((k1 >>> 16) * c1) & 0xffff) << 16)) & 0xffffffff;
        k1 = (k1 << 16) | (k1 >>> 16);
        k1 = (((k1 & 0xffff) * c2) + ((((k1 >>> 16) * c2) & 0xffff) << 16)) & 0xffffffff;
        h1 ^= k1;
    }

    h1 ^= key.length;

    h1 ^= h1 >>> 16;
    h1 = (((h1 & 0xffff) * 0x85ebca6b) + ((((h1 >>> 16) * 0x85ebca6b) & 0xffff) << 16)) & 0xffffffff;
    h1 ^= h1 >>> 13;
    h1 = ((((h1 & 0xffff) * 0xc2b2ae35) + ((((h1 >>> 16) * 0xc2b2ae35) & 0xffff) << 16))) & 0xffffffff;
    h1 ^= h1 >>> 16;

    return h1 >>> 0;
}