[Issue 2352] unittest fails randomly

[d-bugmail at puremagic.com]

http://d.puremagic.com/issues/show_bug.cgi?id=2352


andrei at metalanguage.com changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
             Status|NEW                         |RESOLVED
         Resolution|                            |FIXED




------- Comment #1 from andrei at metalanguage.com  2008-09-10 22:28 -------
The unpredictable seed is meant to vary from one run to the next, not
necessarily from one call to the next, so the test is a bit incorrect. The
function does this:

uint unpredictableSeed()
{
    static uint moseghint = 87324921;
    return cast(uint) (getpid ^ getUTCtime ^ ++moseghint);
}

(Bonus q: what does moseghint mean?)

If it so happens that getUTCtime and moseghint e.g. change only LSB in lockstep
from one call to the next, the returned values will be identical. I changed the
function to this:

uint unpredictableSeed()
{
    static bool seeded;
    static MinstdRand0 rand;
    if (!seeded) {
        rand.seed(getpid ^ getUTCtime);
    }
    return cast(uint) (getUTCtime ^ rand.next);
}

It'll be a bit slower but also quite a bit less predictable. But I also removed
the assert because even with the implementation above, it's not guaranteed that
two successive returns can't be equal.


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