"{ Package: 'stx:libbasic2' }"

Object subclass:#RandomParkMillerUsingFloat

	instanceVariableNames:'seed a m q r'

	classVariableNames:''

	poolDictionaries:''

	category:'Magnitude-Numbers'

!

!RandomParkMillerUsingFloat class methodsFor:'documentation'!

documentation

"

    Like RandomParkMiller, but using floats (instead of LargeInts).

    This makes this one roughly 4 times faster.

    Please read:

        Standard reference by Park and Miller in 

            'Random Number Generators: Good Ones Are Hard to Find',

        Comm. ACM, 31:1192-1201, 1988.

    [see also:]

        Random  - fast, but generates less quality random numbers

        RandomTT800 - another random generator

"

!

testing

"

    |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

        #)

"

! !

!RandomParkMillerUsingFloat 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 "

! !

!RandomParkMillerUsingFloat class methodsFor:'instance creation'!

new

    self initialize.

    ^ super new initialize

! !

!RandomParkMillerUsingFloat methodsFor:'accessing-reading'!

next

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

    seed := self peekValue.

    ^ seed / m

!

nextInteger

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

    seed := self peekValue.

    ^ seed

    "

     self new next

     self new nextInteger

    "

! !

!RandomParkMillerUsingFloat methodsFor:'initialization'!

initialize

    " Set a reasonable Park-Miller starting seed "

    [

        seed := (Time millisecondClockValue bitAnd: 16r3FFFFFFF) bitXor: self hash.

        seed = 0

    ] whileTrue: ["Try again if ever get a seed = 0"].

    a := 16r000041A7 asFloat.    " magic constant =      16807 "

    m := 16r7FFFFFFF asFloat.    " magic constant = 2147483647 "

    q := (m quo: a) asFloat.

    r  := (m \\ a) asFloat.

!

seed:anInteger 

    seed := anInteger

! !

!RandomParkMillerUsingFloat 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 peekValue / m

!

peekValue

    "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|

    hi := (seed quo:q) asFloat.

    lo := seed - (hi * q).

    aLoRHi := (a * lo) - (r * hi).

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

    ^ aLoRHi + m

! !

!RandomParkMillerUsingFloat class methodsFor:'documentation'!

version

    ^ '$Header: /cvs/stx/stx/libbasic2/RandomParkMillerUsingFloat.st,v 1.1 2008-12-16 22:39:51 cg Exp $'

! !

RandomParkMillerUsingFloat initialize!