--- /dev/null Thu Jan 01 00:00:00 1970 +0000
+++ b/RandomParkMiller.st Tue Oct 02 11:33:33 2001 +0200
@@ -0,0 +1,109 @@
+"{ 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
+ ^ '$Header: /cvs/stx/stx/libbasic2/RandomParkMiller.st,v 1.1 2001-10-02 09:33:33 cg Exp $'
+! !
+RandomParkMiller initialize!