"{ Package: 'stx:libbasic2' }"

Object subclass:#RandomParkMiller

	instanceVariableNames:'seed'

	classVariableNames:'PMa PMm PMmu1 PMq PMr'

	poolDictionaries:''

	category:'Magnitude-Numbers'

!

!RandomParkMiller class methodsFor:'documentation'!

documentation

"

    NO WARRANTY

    Another pseudo-random number generator

    |r|

    r := self new.

    (1 to:10) collect:[:i | r next]

    -> should be

        #(

            0.1492432697 

            0.3316330217 

            0.7561964480 

            0.3937015400 

            0.9417831814 

            0.5499291939 

            0.6599625962 

            0.9913545591 

            0.6960744326 

            0.9229878997

        #)

"

! !

!RandomParkMiller class methodsFor:'initialization'!

initialize

    PMa := 16807.

    PMm := 2147483647.    " magic constant = 16807 "

    PMq := 127773.        " magic constant = 2147483647 "

    PMr := 2836.          " quotient (m quo: a) = 44488 "

    PMmu1 := 4.65661E-10  " remainder (m \\ a). = 2836 "

! !

!RandomParkMiller class methodsFor:'instance creation'!

new

    self initialize.

    ^ super new initialize

! !

!RandomParkMiller methodsFor:'accessing-reading'!

next

    " This method generates random instances of Float in the interval 0.0 to 1.0 "

    seed := self nextInteger.

    ^ seed * PMmu1

!

nextInteger

    " This method generates random instances of Integer in the interval 0 to 16r7FFFFFFF. "

    seed := self peekInteger.

    ^ seed

! !

!RandomParkMiller methodsFor:'initialization'!

initialize

    " Set a reasonable Park-Miller starting seed "

    seed := 2345678901

!

seed:anInteger 

    seed := anInteger

! !

!RandomParkMiller methodsFor:'private'!

peek

    " This method answers the next random number that will be generated as a Float in the range [0..1). It answers the same value for all successive message sends. "

    ^ self peekInteger * PMmu1

!

peekInteger

    " This method generates random instances of Integer in the interval 0 to 16r7FFFFFFF. This method does NOT update the seed; repeated sends answer the same value. The algorithm is described in detail in 'Random Number Generators: Good Ones Are Hard to Find' by Stephen K. Park and Keith W. Miller, (Comm. Asso. Comp. Mach., 31(10):1192--1201, 1988). "

    |lo hi aLoRHi answer|

    hi := seed quo:PMq.

    lo := seed rem:PMq.

    aLoRHi := (PMa * lo) - (PMr * hi).

    (aLoRHi > 0) ifTrue:[ ^ aLoRHi ].

    ^ aLoRHi + PMm

! !

!RandomParkMiller class methodsFor:'documentation'!

version

! !

RandomParkMiller initialize!