= StdGen Int Int
instance RandomGen StdGen where
- next = rand1
- split = splitStdGen
+ next = stdNext
+ split = stdSplit
instance Show StdGen where
showsPrec p (StdGen s1 s2) =
readsPrec p = \ r ->
case try_read r of
r@[_] -> r
- _ -> [(unsafePerformIO (mkStdRNG 0), r)] -- because it shouldn't ever fail.
+ _ -> [stdFromString r] -- because it shouldn't ever fail.
where
try_read r = do
(s1, r1) <- readDec (dropWhile isSpace r)
(s2, r2) <- readDec (dropWhile isSpace r1)
return (StdGen s1 s2, r2)
+{-
+ If we cannot unravel the StdGen from a string, create
+ one based on the string given.
+-}
+stdFromString :: String -> (StdGen, String)
+stdFromString s = (mkStdGen num, rest)
+ where (cs, rest) = splitAt 6 s
+ num = foldl (\a x -> x + 3 * a) 1 (map ord cs)
\end{code}
\begin{code}
\end{code}
-\begin{code}
+The class definition - see library report for details.
--- Q: do all of these merit class membership?
+\begin{code}
class Random a where
- randomR :: RandomGen g => (a,a) -> g -> (a,g)
+ -- Minimal complete definition: random and randomR
random :: RandomGen g => g -> (a, g)
+ randomR :: RandomGen g => (a,a) -> g -> (a,g)
- randomRs :: RandomGen g => (a,a) -> g -> [a]
randoms :: RandomGen g => g -> [a]
-
- randomRIO :: (a,a) -> IO a
- randomIO :: IO a
-
randoms g = x : randoms g' where (x,g') = random g
+
+ randomRs :: RandomGen g => (a,a) -> g -> [a]
randomRs ival g = x : randomRs ival g' where (x,g') = randomR ival g
-
+
+ randomIO :: IO a
randomIO = getStdRandom random
- randomRIO range = getStdRandom (randomR range)
+ randomRIO :: (a,a) -> IO a
+ randomRIO range = getStdRandom (randomR range)
\end{code}
\begin{code}
(x, rng') ->
let
scaled_x =
- fromDouble l +
- fromDouble (h-l) *
- (fromIntegral (x::Int) * 4.6566130638969828e-10)
- -- magic number stolen from old HBC code (Random.randomDoubles.)
+ fromDouble ((l+h)/2) +
+ fromDouble ((h-l) / realToFrac intRange) *
+ fromIntegral (x::Int)
in
(scaled_x, rng')
+intRange :: Integer
+intRange = toInteger (maxBound::Int) - toInteger (minBound::Int)
+
iLogBase :: Integer -> Integer -> Integer
iLogBase b i = if i < b then 1 else 1 + iLogBase b (i `div` b)
-rand1 :: StdGen -> (Int, StdGen)
-rand1 (StdGen s1 s2) = (z', StdGen s1'' s2'')
+stdNext :: StdGen -> (Int, StdGen)
+stdNext (StdGen s1 s2) = (z', StdGen s1'' s2'')
where z' = if z < 1 then z + 2147483562 else z
z = s1'' - s2''
s2' = 40692 * (s2 - k' * 52774) - k' * 3791
s2'' = if s2' < 0 then s2' + 2147483399 else s2'
-splitStdGen :: StdGen -> (StdGen, StdGen)
-splitStdGen std@(StdGen s1 s2) = (std, unsafePerformIO (mkStdRNG (fromInt s1)))
-{- StdGen new_s1 new_s2
- where
- -- simple in the extreme..
- new_s1
- | s2 == 2147483562 = 1
- | otherwise = s2 + 1
-
- new_s2
- | s1 == 1 = 2147483398
- | otherwise = s1 - 1
--}
-
+stdSplit :: StdGen -> (StdGen, StdGen)
+stdSplit std@(StdGen s1 s2) = (std, unsafePerformIO (mkStdRNG (fromInt s1)))
\end{code}