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Merge pull request #88 from TomMD/master

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Fix #86 - make randomWord produce uniform randoms
This commit is contained in:
Joseph Kiniry 2014-09-05 13:42:09 -07:00
commit b2f0e3db4e
1 changed files with 5 additions and 22 deletions
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27
src/Cryptol/Testing/Random.hs
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@ -15,10 +15,8 @@ import Cryptol.Eval.Value (BV(..),Value,GenValue(..),ppValue,defaultPPOpts)
import Cryptol.Utils.Panic (panic)
import Cryptol.TypeCheck.AST (Name,Type(..),TCon(..),TC(..),tNoUser)
import System.Random (RandomGen, split, random, randoms, randomR)
import Data.Word (Word64)
import Data.Bits (shiftL, shiftR, (.|.), (.&.), setBit)
import Data.List (unfoldr, foldl', genericTake)
import System.Random (RandomGen, split, random, randomR)
import Data.List (unfoldr, genericTake)
import Control.Monad (forM)
type Gen g = Int -> g -> (Value, g)
@ -103,24 +101,9 @@ randomBit _ g =
-- The size parameter is assumed to vary between 1 and 100, and we use
-- it to generate smaller numbers first.
randomWord :: RandomGen g => Integer -> Gen g
randomWord w sz g =
let (g1,g2) = split g
(bits,g3) = randomR (0, div (sz * fromInteger w + 99) 100) g2
mk num new = (num `shiftL` 64) .|. toInteger (new :: Word64)
x : xs = randoms g1
-- mask most significant word, so that we don't go over `bits`
mask = let r = bits `rem` 64
shR = if r == 0 then 0 else 64 - r
in (-1) `shiftR` shR
x' = x .&. mask
val = foldl' mk 0 $ genericTake (div (bits + 63) 64) (x' : xs)
finalVal = if sz > 1 && bits > 0 then setBit val (bits - 1) else val
in (VWord (BV w finalVal), g3)
randomWord w _sz g =
let (val, g1) = randomR (0,2^w-1) g
in (VWord (BV w val), g1)
-- | Generate a random infinite stream value.
randomStream :: RandomGen g => Gen g -> Gen g