Emulate MSVC rand() function

Monkey Forums/Monkey Code/Emulate MSVC rand() function

Gerry Quinn

(Posted 2011) [#1]

It seems there are some issues with Rnd() at the moment, and I think a lot of folks would be interested in an integer rand() function anyway. I've made a class that replicates in Monkey the algorithm used by MSVC.

Obviously there are better algorithms out there but MSVC is a decent 32-bit LCG that will do the job for most people's gaming purposes.

Strict


' Integer rand() function 
' Same algorithm as MSVC
' Tested on HTML5, Flash, and GLFW


Class MSRand

	Const RAND_MAX:Int = 32767
	
	Const MAX_INT:Int = $FFFFFFFF

	Field seed:Int
			
	Method New()
		srand( 0 )
	End
	
	
	Method New( seedVal:Int )
		srand( seedVal )
	End
	
	
	Method srand:Void( seedVal:Int )
		seed = seedVal & MAX_INT
	End
	
	
	Method rand:Int()
		seed = ( seed*214013 + 2531011 ) & MAX_INT
		Return ( seed Shr 16 ) & RAND_MAX		
	End
	

End


' Note: you need to cut seed down to size with MAX_INT, because otherwise
' on HTML5 the long-ints will run to machine infinity and rand() will start
' returning zeroes.
' Of course it's good for efficiency on long-int platforms too.
' I *hope* there is no platform on which relatively short ints will not
' wrap around to negative numbers, C-fashion.

Gerry Quinn

(Posted 2011) [#2]

Of course, if you want it exactly like MSVC, you can just use global functions etc. rather than a class. I think I will make those as well, in fact, and keep MSRand for special uses. It's handy to be able to just call rand().

Gerry Quinn

(Posted 2011) [#3]

...and into my module of handy functions it goes!

Private
Global seed:Int
Const MAX_INT:Int = $FFFFFFFF
Public


Const RAND_MAX:Int = 32767


Function srand:Void( seedVal:Int )
	seed = seedVal & MAX_INT
End
	
	
Function rand:Int()
	seed = ( seed*214013 + 2531011 ) & MAX_INT
	Return ( seed Shr 16 ) & RAND_MAX		
End