[ODE] dRandInt Crash Fix

[Jaroslav Sinecky]

You're right, dRandInt uses the formula from Numerical Recipes book. But I
think it uses it correctly, I don't see the error and still don't see how
integer greater than n-1 could have come out of it ...

 return (int) ( (double)(n) * (double)dRand() / 4294967296.0 )

Because (double)dRand()/((double)RAND_MAX+1.0) should never reach 1.0 and
conversion to int just truncates at the floating point.
And this number 4294967296.0 should really be RAND_MAX+1 in our case
(0xffffffff + 1).

Maybe because some flointing point precision error in double division??

I was so worried, that I created a very simple test where I substitute
dRand() for its possibly max value...

int dRandInt (int n)
{
  double a = double(n) / 4294967296.0;
  int ret = (int) (double(0xffffffff) * a);
  return ret;
}

int _main(int argc, _CHAR* argv[])
{
	int i;
	i = dRandInt(1);
	i = dRandInt(1000);
	i = dRandInt(100000);
	i = dRandInt(2147483647); // max possible signed int value

	return 0;
}

And it works without problem!
Maybe on some other platform/compiler will not?


I have no neurona left to figure how your xor-folding method works, but did
you try it? Do you think It can be faster then the original version? (on pc
that has hw double support)

Cheers!
Jaroslav