random state

About random-state

This is a collection of pseudo random number generators (PRNGs). While Common Lisp does provide a RANDOM function, it does not allow the user to pass an explicit seed, nor to portably exchange the random state between implementations. This can be a headache in cases like games, where a controlled seeding process is very useful.

How To

For both curiosity and convenience, this library offers multiple algorithms to generate random numbers, as well as a bunch of generally useful methods to produce desired ranges.

(loop with generator = (random-state:make-generator :mersenne-twister-32 123)
      repeat 10
      collect (random-state:random-int generator 0 10))
; => (8 10 9 5 3 10 9 2 9 2)

Several methods to compute random numbers in certain ranges are provided in advance: random-byte, random-bytes, random-sequence, random-unit, random-float, and random-int. Each of those can also be used with just the name of the generator you'd like to use as the first argument, in which case a global instance will be used.

For generators that are hash-based, such as squirrel, additional noise functions are provided: random-1d, random-2d, and random-3d, and some functions to manipulate the stepping of the generator: index, and rewind.