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"Random number functions", by badjim

The Blitz random number functions are bugged, since numbers produced by a given seed can be different from one machine to the next. These replacement functions are consistent across machines.

Code

;put these two lines at the start of your code to initialise it
Dim RandGenArray(56)
SeedRnd

; This will replace SeedRnd
Function SeedRnd(seed=0)
     RandGenArray(54)=1
     RandGenArray(55)=0
     RandGenArray(56)=31
     
     For index=0 To 53
          RandGenArray(index)=(seed + index) * index * index * 86865467
     Next
     
     For count=1 To 1000
          Random
     Next
End Function

; This will return a random 32 bit integer. It's the fastest function
; because it doesn't mess around with it's output
Function Random()
     If RandGenArray(55)=54
          RandGenArray(55)=0
     Else
          current=RandGenArray(55)+1
          RandGenArray(55)=current
     EndIf
     
     If RandGenArray(56)=54
          RandGenArray(56)=0
     Else
          RandGenArray(56)=RandGenArray(56)+1
     EndIf
     
     RandGenArray(current)=RandGenArray(current)+RandGenArray(RandGenArray(56))

Return RandGenArray(current)
End Function

; The new Rnd() function. Doesn't support the low value. Sorry
Function Rnd#(max#)
     If RandGenArray(55)=54
          RandGenArray(55)=0
     Else
          current=RandGenArray(55)+1
          RandGenArray(55)=current
     EndIf
     
     If RandGenArray(56)=54
          RandGenArray(56)=0
     Else
          RandGenArray(56)=RandGenArray(56)+1
     EndIf
     
     RandGenArray(current)=RandGenArray(current)+RandGenArray(RandGenArray(56))
     
     ans#=RandGenArray(current)
     ans=(Float(RandGenArray(current)) + 2147483648.0) * 0.00000000023283064365386962890625 * max
     ans=(Float(RandGenArray(current)) + 2147483648.0) * 0.00000000023283064365386962890625 * max

Return (Float(RandGenArray(current)) + 2147483648.0) * 0.00000000023283064365386962890625 * max
End Function

; The new Rand() function. Also doesn't support the low value.
Function Rand(max)
     If RandGenArray(55)=54
          RandGenArray(55)=0
     Else
          current=RandGenArray(55)+1
          RandGenArray(55)=current
     EndIf
     
     If RandGenArray(56)=54
          RandGenArray(56)=0
     Else
          RandGenArray(56)=RandGenArray(56)+1
     EndIf
     
     RandGenArray(current)=RandGenArray(current)+RandGenArray(RandGenArray(56))

If max>0
          x=(RandGenArray(current) And $7FFFFFFF)/max
          If (x+1)*max<0
               Return Rand(max)
          Else
               Return (RandGenArray(current) And $7FFFFFFF)+1-(x*max)
          EndIf
     Else
          If (RandGenArray(current)>max) And (RandGenArray(current)<0)
               Return Rand(max)
          Else
               Return RandGenArray(current)
          EndIf
     EndIf

Return RandGenArray(current)
End Function

; An alternative version of the Rand() function. It's a bit faster than
; the basic Rand() but with different results that are possibly less random
; It keeps the running total low with a nice fast While function, instead of
; doing a modulo on the output. This means the results of later random numbers
; with any of these functions could be artificially low if you use this.

;  Also note that a While loop is fast for just one iteration or so but very slow
; when reducing a nine digit number by about 5 at a time. It's also very bad with
; negative numbers. Therefore you should write code to reduce RandGenArray elements 0-54
; to low positive numbers before using this. Which makes this only suitable if you
; want to churn out millions of numbers without using Rnd or Random.
Function Rand2(max)
     If RandGenArray(55)=54
          RandGenArray(55)=0
     Else
          current=RandGenArray(55)+1
          RandGenArray(55)=current
     EndIf
     
     If RandGenArray(56)=54
          RandGenArray(56)=0
     Else
          RandGenArray(56)=RandGenArray(56)+1
     EndIf
     
     RandGenArray(current)=RandGenArray(current)+RandGenArray(RandGenArray(56))

While RandGenArray(current)>max
          RandGenArray(current)=RandGenArray(current)-max
     Wend

Return RandGenArray(current)
End Function

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