Exponentially Distributed Random Variates with mean 500 in C

I want to create bunch of random numbers but it should be exponentially distributed. I should use Steve Park & Dave Geyer's Random Number Generation basically I need to add a function to create this. So I did this but it seems it stuck in while. How can I fix this? Thanks in advance!

double RandomRV(void) //Exponential Distribution

{

double i;
double numb;

i = Random();

numb = i / MODULUS;

while (numb < 1.e-6)
{
    i = Random();
    numb = i / MODULUS;
}

return((double)-500*log(numb));

}