Pseudo-Zufallszahlengeneratoren.
> module Random ( randomInts,
> random2Ints, random2Doubles
> )
> where
A simple random number generator taken from Paulson.
> randomInts :: Int -> [Int]
> randomInts seed = seed:randomInts ((16807 * seed) `mod` 2147483647)
An advanced random number generator taken from the hbc library.
Use seeds `s1' in 1..2147483562 and `s2' in 1..2147483398 to generate
an infinite list of random Ints.
> random2Ints :: Int -> Int -> [Int]
> random2Ints s1 s2 =
> if 1 <= s1 && s1 <= 2147483562 then
> if 1 <= s2 && s2 <= 2147483398 then
> rands s1 s2
> else
> error "random2Ints: Bad second seed."
> else
> error "random2Ints: Bad first seed."
> rands :: Int -> Int -> [Int]
> rands s1 s2 =
> let
> k = s1 `div` 53668
> s1' = 40014 * (s1 - k * 53668) - k * 12211
> s1'' = if s1' < 0 then s1' + 2147483563 else s1'
>
> k' = s2 `div` 52774
> s2' = 40692 * (s2 - k' * 52774) - k' * 3791
> s2'' = if s2' < 0 then s2' + 2147483399 else s2'
>
> z = s1'' - s2''
> in if z < 1 then z + 2147483562 : rands s1'' s2''
> else z : rands s1'' s2''
Same values for s1 and s2 as above, generates an infinite list of
Doubles uniformly distibuted in (0,1).
> random2Doubles :: Int -> Int -> [Double]
> random2Doubles s1 s2 =
> map (\x -> fromInt x * 4.6566130638969828e-10) (random2Ints s1 s2)