It's odd to have the documentation in a .docx file in the repo. The code itself is not very readable. The core of it is something like (simplified):

    function mix(uint64 a, uint64 b) {
        a ^= secret
        b ^= seed
        hi, lo = mul128(a, b)
        seed = hi ^ lo
    }

It's elegantly simple, but depends critically on 'secret' not appearing in the data.