[OpenSTA-devel] When is Random not random?

[Wickersham, P. <Pet...@di...>]

Well,

It would appear that the random function used within OpenSTA is not very
random.

I was having some issues with using RANDOM on a range of 1 - 120000. It
didn't appear to me that it was very random since I seemed to get
repeating numbers pretty quickly.=20

So, I looked at the source and the code appears to use srand() everytime
it calls rand() with the last result from calling rand(). However, this
actually ends up producing more collisions more quickly than just
calling srand() once.=20

I took the same approach in a sample app and ran a loop for 1000 times
generating random numbers between 1 and 30000. Using srand() once
produced 974 unique numbers. Using srand() every time with the last
result of rand() produce 173 unique numbers.

I have not had the opportunity to configure the source to build it and
test any changes. In fact, I have the CVS HEAD, so that might be
problematic if I read the site correctly. Not to mention that I
currently have Visual Studio 2003

-peter=20