Seeded PRNG in JavaScript

Below is a multiply-with-carry (MWC) random generator with a pretty long period, adapted from wikipedia Random Number Generators:

// Takes any integer
Math.seed = function(s) {
    var m_w = s;
    var m_z = 987654321;
    var mask = 0xffffffff;
    return function() 
    // Returns number between 0 (inclusive) and 1.0 (exclusive),
    // just like Math.random().
    {
        m_z = (36969 * (m_z & 65535) + (m_z >> 16)) & mask;
        m_w = (18000 * (m_w & 65535) + (m_w >> 16)) & mask;
        var result = ((m_z << 16) + m_w) & mask;
        result /= 4294967296;
        return result + 0.5;
    }
}

Another fast and simple PRNG, without magic numbers:

Math.seed = function(s) {
    return function() {
        s = Math.sin(s) * 10000;
        return s - Math.floor(s);
    };
};

You can replace the default PRNG of JavaScript by, e.g.,

Math.random = Math.seed(Math.round(Math.seed(42)*10000));

Reference

1. http://stackoverflow.com/questions/521295/javascript-random-seeds/521323
2. https://github.com/davidbau/seedrandom