Savage.Internal.Seed

This is a port of "Fast Splittable Pseudorandom Number Generators" by Steele et. al. [1].

The paper's algorithm provides decent randomness for most purposes but sacrifices cryptographic-quality randomness in favor of speed. The original implementation is tested with DieHarder and BigCrush; see the paper for details.

This implementation, originally from [2], is a port from the paper.

It also takes in to account the SplittableRandom.java source code in OpenJDK v8u40-b25 as well as splittable_random.ml in Jane Street's standard library overlay (kernel) v113.33.03, and Random.fs in FsCheck v3.

Other than the choice of initial seed for from this port should be faithful. Currently, we have not rerun the DieHarder, or BigCrush tests on this implementation.

1. Guy L. Steele, Jr., Doug Lea, Christine H. Flood Fast splittable pseudorandom number generators Comm ACM, 49(10), Oct 2014, pp453-472.
2. Nikos Baxevanis https://github.com/moodmosaic/SplitMix/blob/master/SplitMix.hs

Documentation

data Seed

A splittable random number generator.

Constructors

Seed

Fields

• seedValue :: !Int64
• seedGamma :: !Int64

  must be an odd number

Instances

Eq Seed

Methods

(==) :: Seed -> Seed -> Bool

(/=) :: Seed -> Seed -> Bool

Ord Seed

Methods

compare :: Seed -> Seed -> Ordering

(<) :: Seed -> Seed -> Bool

(<=) :: Seed -> Seed -> Bool

(>) :: Seed -> Seed -> Bool

(>=) :: Seed -> Seed -> Bool

max :: Seed -> Seed -> Seed

min :: Seed -> Seed -> Seed

Read Seed

Methods

readsPrec :: Int -> ReadS Seed

readList :: ReadS [Seed]

readPrec :: ReadPrec Seed

readListPrec :: ReadPrec [Seed]

Show Seed

Methods

showsPrec :: Int -> Seed -> ShowS

show :: Seed -> String

showList :: [Seed] -> ShowS

RandomGen Seed

Methods

next :: Seed -> (Int, Seed)

genRange :: Seed -> (Int, Int)

split :: Seed -> (Seed, Seed)

random :: MonadIO m => m Seed

Create a random Seed using an effectful source of randomness.

from :: Int64 -> Seed

Create a Seed using an Int64.

split :: Seed -> (Seed, Seed)

Splits a random number generator in to two.

nextInteger :: Integer -> Integer -> Seed -> (Integer, Seed)

Generate a random Integer in the [inclusive,inclusive] range.

nextDouble :: Double -> Double -> Seed -> (Double, Seed)

Generate a random Double in the [inclusive,exclusive) range.

Internal

These functions are exported in case you need them in a pinch, but are not part of the public API and may change at any time, even as part of a minor update.

goldenGamma :: Int64

A predefined gamma value's needed for initializing the "root" instances of Seed. That is, instances not produced by splitting an already existing instance.

We choose: the odd integer closest to 2^64/φ, where φ = (1 + √5)/2 is the golden ratio.

nextInt64 :: Seed -> (Int64, Seed)

Generate a random Int64.

nextInt32 :: Seed -> (Int32, Seed)

Generate a random Int32.

mix64 :: Int64 -> Int64

mix64variant13 :: Int64 -> Int64

mix32 :: Int64 -> Int32

mixGamma :: Int64 -> Int64