| Safe Haskell | None |
|---|---|
| Language | Haskell98 |
Data.Random.Source.MWC
Contents
Description
This module defines the following instances:
instance RandomSource (ST s) (Gen s) instance RandomSource IO (Gen RealWorld)
Documentation
State of the pseudo-random number generator. It uses mutable state so same generator shouldn't be used from the different threads simultaneously.
Instances
RealWorld is deeply magical. It is primitive, but it is not
unlifted (hence ptrArg). We never manipulate values of type
RealWorld; it's only used in the type system, to parameterise State#.
Instances
| RandomSource IO (Gen RealWorld) Source # | |
Defined in Data.Random.Source.MWC Methods getRandomPrimFrom :: Gen RealWorld -> Prim t -> IO t Source # getRandomWord8From :: Gen RealWorld -> IO Word8 Source # getRandomWord16From :: Gen RealWorld -> IO Word16 Source # getRandomWord32From :: Gen RealWorld -> IO Word32 Source # getRandomWord64From :: Gen RealWorld -> IO Word64 Source # getRandomDoubleFrom :: Gen RealWorld -> IO Double Source # getRandomNByteIntegerFrom :: Gen RealWorld -> Int -> IO Integer Source # | |
initialize :: (PrimMonad m, Vector v Word32) => v Word32 -> m (Gen (PrimState m)) #
Create a generator for variates using the given seed, of which up to 256 elements will be used. For arrays of less than 256 elements, part of the default seed will be used to finish initializing the generator's state.
Examples:
initialize (singleton 42)
initialize (fromList [4, 8, 15, 16, 23, 42])
If a seed contains fewer than 256 elements, it is first used
verbatim, then its elements are xored against elements of the
default seed until 256 elements are reached.
If a seed contains exactly 258 elements, then the last two elements
are used to set the generator's initial state. This allows for
complete generator reproducibility, so that e.g. gen' == gen in
the following example:
gen' <-initialize.fromSeed=<<save
In the MWC algorithm, the carry value must be strictly smaller than the multiplicator (see https://en.wikipedia.org/wiki/Multiply-with-carry). Hence, if a seed contains exactly 258 elements, the carry value, which is the last of the 258 values, is moduloed by the multiplicator.
Note that if the first carry value is strictly smaller than the multiplicator,
all subsequent carry values are also strictly smaller than the multiplicator
(a proof of this is in the comments of the code of uniformWord32), hence
when restoring a saved state, we have the guarantee that moduloing the saved
carry won't modify its value.