"{ Package: 'stx:libbasic2' }"

Object subclass:#RandomBlumBlumShub

	instanceVariableNames:'p q m seed'

	classVariableNames:''

	poolDictionaries:''

	category:'Magnitude-Numbers'

!

!RandomBlumBlumShub class methodsFor:'documentation'!

documentation

"

    NO WARRANTY

    This generator uses the blum blub shub algorithm to generate random numbers.

    It is very slow, but considered to provide good random numbers.

    RandomBlumBlumShub new nextInteger

    [see also:]

        RandomGenerator - the default; uses the machine's /dev/random if available

        Random  - fast, but generates less quality random numbers

        RandomTT800 - another random generator

        RandomParkMiller - another random generator

        RandomMT19937 - another random generator

        RandomKISS - another random generator

        exept:libcrypt - a library containing more stuff based on hashes and cyphers

    [author:]

        Claus Gittinger.

"

! !

!RandomBlumBlumShub class methodsFor:'instance creation'!

new

    ^ self basicNew 

        initialize;

        seed:(Random randomSeed)

!

new:seed

    self isSupported ifFalse:[ self error:'this generator needs a cpu with rdgen instruction' ].

    ^ self basicNew 

        initialize;

        seed:seed

! !

!RandomBlumBlumShub methodsFor:'initialization'!

initialize

    "The two primes, p and q, should both be congruent to 3 (mod 4)"

    p := 615389388455725613122981570401989286707.

    q := 8936277569639798554773638405675965349567.

    m := p * q.

    "/ (p \\ 4) = 3 ifFalse:[ self halt: 'unsuitable p' ].

    "/ (q \\ 4) = 3 ifFalse:[ self halt: 'unsuitable p' ].

    "

     self new initialize

    "

!

seed:seedArg

    seed := seedArg.

    self assert:(seed < m).

    self assert:(seed gcd:m) = 1.

! !

!RandomBlumBlumShub methodsFor:'random numbers'!

nextBoolean

    "generates the next random boolean"

    seed := seed*seed \\ m.

    ^ seed bitTest:1

!

nextInteger

    "generates the next integer in 0..FFFFFFFF"

    |num|

    num := 0.

    32 timesRepeat:[

        seed := (seed * seed) \\ m.

        num := (num<<1) + (seed bitAnd:1).

    ].

    ^ num.

    "

     self new nextInteger.

     |r|

     r := self new

     100 timesRepeat:[ Transcript showCR:r nextInteger].

    "

! !

!RandomBlumBlumShub class methodsFor:'documentation'!

version

    ^ '$Header: /cvs/stx/stx/libbasic2/RandomBlumBlumShub.st,v 1.1 2014-10-02 16:24:30 cg Exp $'

!

version_CVS

    ^ '$Header: /cvs/stx/stx/libbasic2/RandomBlumBlumShub.st,v 1.1 2014-10-02 16:24:30 cg Exp $'

! !