MS Bug or MSDN/Documentation typo???   

The Rnd() Function doesn't appear to always work as it should (according to 
the documentation / MSDN info for the Rnd() Function):

{Begin Excerpt from VS 2008 documentation}
"
To produce random integers in a given range, use the following formula.

Visual Basic :  
randomvalue = CInt(Int((upperbound - lowerbound + 1) * Rnd() + lowerbound))


 

Here, upperbound is the highest number in the range, and lowerbound is the 
lowest number in the range.

"
{End Excerpt from VS 2008 documentation}

Sounds straight forward enough, however the following VB code demonstrates 
that the Rnd() function does not always behave as it should:


        
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        Dim upperbound As Integer = 254
        Dim lowerbound As Integer = 128
        Dim randomvalue As Integer

        Dim intX As Integer

        Randomize()
        For intX = 0 To 100000000

            randomvalue = CInt(Int((upperbound - lowerbound + 1) * Rnd() + 
lowerbound))

            If randomvalue > upperbound Then Console.WriteLine("UPPER BOUND 
EXCEEDED!!!: randomvalue=" & randomvalue & " But upperbound=" & upperbound)

        Next

        Console.WriteLine("Finished!")
        
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The above code writes a a message to the console whenever the Rnd() function 
returns a randomvalue that is greater than the upperbound specified (as per 
the documentation).
On running this code I see that there are instances where thr Rnd function 
does that.

I would be interested to see if other people's computers produce the same 
results - it seems that they certainly should!

So is this a bug in Rnd() or is the VS/MSDN documentation wrong?


Many thanks.

date: Fri, 14 Mar 2008 09:40:03 -0700   author:   Smudge