2 % (c) The GRASP/AQUA Project, Glasgow University, 1995-99
6 The June 1988 (v31 #6) issue of the Communications of the ACM has an
7 article by Pierre L'Ecuyer called, "Efficient and Portable Combined
8 Random Number Generators". Here is the Portable Combined Generator of
9 L'Ecuyer for 32-bit computers. It has a period of roughly 2.30584e18.
11 Transliterator: Lennart Augustsson
13 sof 1/99 - code brought (kicking and screaming) into the new Random
19 RandomGen(next, split)
22 , Random ( random, randomR,
31 import CPUTime (getCPUTime)
35 import PrelNumExtra ( float2Double, double2Float )
38 import Char ( isSpace, chr, ord )
39 import Time (getClockTime, ClockTime(..))
44 class RandomGen g where
54 instance RandomGen StdGen where
58 instance Show StdGen where
59 showsPrec p (StdGen s1 s2) =
64 instance Read StdGen where
68 _ -> [stdFromString r] -- because it shouldn't ever fail.
71 (s1, r1) <- readDec (dropWhile isSpace r)
72 (s2, r2) <- readDec (dropWhile isSpace r1)
73 return (StdGen s1 s2, r2)
76 If we cannot unravel the StdGen from a string, create
77 one based on the string given.
79 stdFromString :: String -> (StdGen, String)
80 stdFromString s = (mkStdGen num, rest)
81 where (cs, rest) = splitAt 6 s
82 num = foldl (\a x -> x + 3 * a) 1 (map ord cs)
86 mkStdGen :: Int -> StdGen -- why not Integer ?
88 | s < 0 = mkStdGen (-s)
89 | otherwise = StdGen (s1+1) (s2+1)
91 (q, s1) = s `divMod` 2147483562
92 s2 = q `mod` 2147483398
94 createStdGen :: Integer -> StdGen
96 | s < 0 = createStdGen (-s)
97 | otherwise = StdGen (toInt (s1+1)) (toInt (s2+1))
99 (q, s1) = s `divMod` 2147483562
100 s2 = q `mod` 2147483398
104 The class definition - see library report for details.
108 -- Minimal complete definition: random and randomR
109 random :: RandomGen g => g -> (a, g)
110 randomR :: RandomGen g => (a,a) -> g -> (a,g)
112 randoms :: RandomGen g => g -> [a]
113 randoms g = x : randoms g' where (x,g') = random g
115 randomRs :: RandomGen g => (a,a) -> g -> [a]
116 randomRs ival g = x : randomRs ival g' where (x,g') = randomR ival g
119 randomIO = getStdRandom random
121 randomRIO :: (a,a) -> IO a
122 randomRIO range = getStdRandom (randomR range)
126 instance Random Int where
127 randomR (a,b) g = randomIvalInteger (toInteger a, toInteger b) g
128 random g = randomR (minBound,maxBound) g
130 instance Random Char where
132 case (randomIvalInteger (toInteger (ord a), toInteger (ord b)) g) of
134 random g = randomR (minBound,maxBound) g
136 instance Random Bool where
138 case (randomIvalInteger (toInteger (bool2Int a), toInteger (bool2Int b)) g) of
139 (x, g) -> (int2Bool x, g)
147 random g = randomR (minBound,maxBound) g
149 instance Random Integer where
150 randomR ival g = randomIvalInteger ival g
151 random g = randomR (toInteger (minBound::Int), toInteger (maxBound::Int)) g
153 instance Random Double where
154 randomR ival g = randomIvalDouble ival id g
155 random g = randomR (0::Double,1) g
157 -- hah, so you thought you were saving cycles by using Float?
158 instance Random Float where
159 randomR (a,b) g = randomIvalDouble (float2Double a, float2Double b) double2Float g
160 random g = randomIvalDouble (0::Double,1) double2Float g
166 mkStdRNG :: Integer -> IO StdGen
169 (TOD sec _) <- getClockTime
170 return (createStdGen (sec * 12345 + ct + o))
172 randomIvalInteger :: (RandomGen g, Num a) => (Integer, Integer) -> g -> (a, g)
173 randomIvalInteger (l,h) rng
174 | l > h = randomIvalInteger (h,l) rng
175 | otherwise = case (f n 1 rng) of (v, rng') -> (fromInteger (l + v `mod` (k+1)), rng')
186 f (n-1) (fromInt x + acc * b) g'
188 randomIvalDouble :: (RandomGen g, Fractional a) => (Double, Double) -> (Double -> a) -> g -> (a, g)
189 randomIvalDouble (l,h) fromDouble rng
190 | l > h = randomIvalDouble (h,l) fromDouble rng
192 case (randomIvalInteger (toInteger (minBound::Int), toInteger (maxBound::Int)) rng) of
196 fromDouble ((l+h)/2) +
197 fromDouble ((h-l) / realToFrac intRange) *
198 fromIntegral (x::Int)
203 intRange = toInteger (maxBound::Int) - toInteger (minBound::Int)
205 iLogBase :: Integer -> Integer -> Integer
206 iLogBase b i = if i < b then 1 else 1 + iLogBase b (i `div` b)
208 stdNext :: StdGen -> (Int, StdGen)
209 stdNext (StdGen s1 s2) = (z', StdGen s1'' s2'')
210 where z' = if z < 1 then z + 2147483562 else z
214 s1' = 40014 * (s1 - k * 53668) - k * 12211
215 s1'' = if s1' < 0 then s1' + 2147483563 else s1'
218 s2' = 40692 * (s2 - k' * 52774) - k' * 3791
219 s2'' = if s2' < 0 then s2' + 2147483399 else s2'
221 stdSplit :: StdGen -> (StdGen, StdGen)
222 stdSplit std@(StdGen s1 s2) = (std, unsafePerformIO (mkStdRNG (fromInt s1)))
228 global_rng :: MutableVar RealWorld StdGen
229 global_rng = unsafePerformIO $ do
233 setStdGen :: StdGen -> IO ()
234 setStdGen sgen = stToIO (writeVar global_rng sgen)
236 getStdGen :: IO StdGen
237 getStdGen = stToIO (readVar global_rng)
239 newStdGen :: IO StdGen
242 let (a,b) = split rng
246 getStdRandom :: (StdGen -> (a,StdGen)) -> IO a
249 let (v, new_rng) = f rng