[project @ 1997-05-19 04:51:33 by sof]

new std lib

diff --git a/ghc/lib/required/Random.lhs b/ghc/lib/required/Random.lhs
new file mode 100644 (file)
index 0000000..faae80a
--- /dev/null
+++ b/ghc/lib/required/Random.lhs
@@ -0,0 +1,67 @@
+
+This module implements a (good) random number generator.
+
+The June 1988 (v31 #6) issue of the Communications of the ACM has an
+article by Pierre L'Ecuyer called, "Efficient and Portable Combined
+Random Number Generators".  Here is the Portable Combined Generator of
+L'Ecuyer for 32-bit computers.  It has a period of roughly 2.30584e18.
+
+Transliterator: Lennart Augustsson
+
+\begin{code}
+module Random
+       (
+        random, 
+        randomIO
+        ) where
+
+import CPUTime (getCPUTime)
+import Time (getClockTime, ClockTime(..))
+
+randomIO :: (Integer, Integer) -> IO [Integer]
+randomIO lh = do
+    ct          <- getCPUTime
+    (TOD sec _) <- getClockTime
+    return (random lh (sec * 12345 + ct))
+
+random :: (Integer, Integer) -> Integer -> [Integer]
+random (l, h) s =
+    if l > h then error "Random.random: Empty interval" else
+    if s < 0 then random (l, h) (-s) else
+       let (q, s1) = s `divMod` 2147483562
+           s2 = q `mod` 2147483398
+            k = h-l + 1
+            b = 2147483561
+            n = iLogBase b k
+           f is = let (xs, is') = splitAt n is
+                   in  foldr (\ i r -> fromInt i + r * b) 0 xs `mod` k + l : f is'
+       in  f (randomInts (toInt (s1+1)) (toInt (s2+1)))
+
+iLogBase b i = if i < b then 1 else 1 + iLogBase b (i `div` b)
+
+-- Use seeds s1 in 1..2147483562 and s2 in 1..2147483398 to generate
+-- an infinite list of random Ints.
+randomInts :: Int -> Int -> [Int]
+randomInts s1 s2 =
+    if 1 <= s1 && s1 <= 2147483562 then
+       if 1 <= s2 && s2 <= 2147483398 then
+           rands s1 s2
+       else
+           error "randomInts: Bad second seed."
+    else
+       error "randomInts: Bad first seed."
+
+rands :: Int -> Int -> [Int]
+rands s1 s2 = z' : rands s1'' s2''
+       where   z'   = if z < 1 then z + 2147483562 else z
+               z    = s1'' - s2''
+
+               k    = s1 `quot` 53668
+               s1'  = 40014 * (s1 - k * 53668) - k * 12211
+               s1'' = if s1' < 0 then s1' + 2147483563 else s1'
+    
+               k'   = s2 `quot` 52774
+               s2'  = 40692 * (s2 - k' * 52774) - k' * 3791
+               s2'' = if s2' < 0 then s2' + 2147483399 else s2'
+       
+\end{code}