--- /dev/null	Thu Jan 01 00:00:00 1970 +0000
+++ b/RandomParkMillerUsingFloat.st	Tue Dec 16 23:39:51 2008 +0100
@@ -0,0 +1,142 @@
+"{ 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!