This is a Marsaglia xorshift generator, implemented with a 3 x 32-bit pool, for a 2^96 period. At the time this hit a sweet spot for period vs speed.
Don't.
I put this up here only for historical purposes, as it used to be on my personal site from 2004. Nowadays a 2 x 64 bit xor shift generator has a longer period for fewer clock cycles. There are also many (arguably better) options than the xor-shift RNGs as well. The XOR Shift article at Wikipedia has a short discussion of tradeoffs about this class of generator.