This is a mildly ported version of Bob Jenkins' ISAAC, a fast 32-bit CSPRNG.

More information on the algorithm can be found at
http://www.burtleburtle.net/bob/rand/isaacafa.html

The code emits a stream of random uint32 and also supports Go's
crypto/cipher.Stream interface. Its output matches the official test vectors
for ISAAC, but I can't make any guarantees about the cryptographic qualities of
this code (especially the stream mode). Use at your own risk.