How/why does this noise function work?

Question

How/why does this noise function work?

function noise(x)
    x = (x << 13) ^ x;
    return (1.0 - ((x * (x * x * 15731 + 789221) + 1376312589) & 0x7fffffff)
               / 1073741824.0);

I've found it in several places with different primes, but couldn't find an actual explanation of why/how it works.

I know what the code itself is doing (shift, xor, multiply-and-overflow, bitwise-and w/ intmax - 1, etc), but I don't get why those things are done or how it results in acceptable noise.

Why are these operations, why this order? Why primes? I know "because non-primes can generate observable patterns", but why is that?

Why divide by (2**32 - 1)/2? or rather, why does that give a 0..2 value?

Answer 1

It is a random noise generator. Did Google search on: "noise function" 0x7fffffff

See: http://www.qwerty-games.com/viewvc/Sardon3D/Branches/Networking/src/Noise.cpp?view=markup

http://libnoise.sourceforge.net/noisegen/index.html