What random number generator does NuPIC use?

Can anyone tell me what random number generator is used by NuPIC - specifically to initialize the states of a spatial pooler.
Is an external generator used (e.g. a Python or C math library), or is a Numenta implemented algorithm used?

I’m on Windows, using Python 2.7.

From the code it looks like the implementation is within nupic/bindings/_math.pyd, however I can’t see any source code for that library.
Is the source code available, and I’m just not finding it?

There is an old discussion proposing a custom implementation (Proposal: Universal Random Number Generator), but nothing indicating what was eventually done/implemented.

I think it is in cpp.