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{-# LANGUAGE CPP, ForeignFunctionInterface #-}
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--------------------------------------------------------------------
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-- Module : System.Random.Mersenne.Pure64
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-- Copyright : Copyright (c) 2008, Don Stewart <dons@galois.com>
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-- Maintainer : Don Stewart <dons@galois.com>
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-- Stability : experimental
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-- Portability: CPP, FFI
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-- Tested with: GHC 6.8.3
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-- A purely functional binding 64 bit binding to the classic mersenne
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-- twister random number generator. This is more flexible than the
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-- impure 'mersenne-random' library, at the cost of being a bit slower.
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-- This generator is however, many times faster than System.Random,
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-- and yields high quality randoms with a long period.
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-- This generator may be used with System.Random, however, that is
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-- likely to be slower than using it directly.
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module System.Random.Mersenne.Pure64 (
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-- * The random number generator
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PureMT -- abstract: RandomGen
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, pureMT -- :: Word64 -> PureMT
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, newPureMT -- :: IO PureMT
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-- * Low level access to the generator
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, randomInt -- :: PureMT -> (Int ,PureMT)
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, randomWord -- :: PureMT -> (Word ,PureMT)
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, randomInt64 -- :: PureMT -> (Int64 ,PureMT)
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, randomWord64 -- :: PureMT -> (Word64,PureMT)
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, randomDouble -- :: PureMT -> (Double,PureMT)
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------------------------------------------------------------------------
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import System.Random.Mersenne.Pure64.MTBlock
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-- | Create a PureMT generator from a 'Word64' seed.
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pureMT :: Word64 -> PureMT
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pureMT = mkPureMT . seedBlock . fromIntegral
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-- | Create a new PureMT generator, using the clocktime as the base for the seed.
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newPureMT :: IO PureMT
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(TOD sec psec) <- getClockTime
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return $ pureMT (fromIntegral $ sec * 1013904242 + psec + ct)
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------------------------------------------------------------------------
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-- System.Random interface.
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-- Being purely functional, the PureMT generator is an instance of
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-- RandomGen. However, it doesn't support 'split' yet.
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instance RandomGen PureMT where
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split = error "System.Random.Mersenne.Pure: unable to split the mersenne twister"
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------------------------------------------------------------------------
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-- Direct access to Int, Word and Double types
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-- | Yield a new 'Int' value from the generator, returning a new
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-- generator and that 'Int'. The full 64 bits will be used on a 64 bit machine.
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randomInt :: PureMT -> (Int,PureMT)
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randomInt g = (fromIntegral i, g')
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where (i, g') = randomWord64 g
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{-# INLINE randomInt #-}
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-- | Yield a new 'Word' value from the generator, returning a new
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-- generator and that 'Word'.
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randomWord :: PureMT -> (Word,PureMT)
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randomWord g = (fromIntegral i, g')
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where (i, g') = randomWord64 g
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{-# INLINE randomWord #-}
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-- | Yield a new 'Int64' value from the generator, returning a new
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-- generator and that 'Int64'.
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randomInt64 :: PureMT -> (Int64,PureMT)
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randomInt64 g = (fromIntegral i, g')
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where (i, g') = randomWord64 g
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{-# INLINE randomInt64 #-}
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-- | Efficiently yield a new 53-bit precise 'Double' value, and a new generator.
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randomDouble :: PureMT -> (Double,PureMT)
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randomDouble g = (fromIntegral (i `div` 2048) / 9007199254740992, g')
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where (i, g') = randomWord64 g
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{-# INLINE randomDouble #-}
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-- | Yield a new 'Word64' value from the generator, returning a new
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-- generator and that 'Word64'.
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randomWord64 :: PureMT -> (Word64,PureMT)
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randomWord64 (PureMT block i nxt) = (mixWord64 (block `lookupBlock` i), mt)
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mt | i < blockLen-1 = PureMT block (i+1) nxt
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| otherwise = mkPureMT nxt
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{-# INLINE randomWord64 #-}
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-- | 'PureMT', a pure mersenne twister pseudo-random number generator
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data PureMT = PureMT {-# UNPACK #-} !MTBlock {-# UNPACK #-} !Int MTBlock
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instance Show PureMT where
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show _ = show "<PureMT>"
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-- create a new PureMT from an MTBlock
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mkPureMT :: MTBlock -> PureMT
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mkPureMT block = PureMT block 0 (nextBlock block)
added
removed
System/Random/Mersenne/Pure64.hs
