Primality test function doesn't work on large numbers?

[Eugene Wissner via Digitalmars-d-learn]

On Tuesday, 10 January 2017 at 03:02:40 UTC, Elronnd wrote:
> Thank you!  Would you mind telling me what you changed aside 
> from pow() and powm()?  diff isn't giving me readable results, 
> since there was some other stuff I trimmed out of the original 
> file.  Also, while this is a *lot* better, I still get some lag 
> generating 1024-bit primes and I can't generate larger primes 
> in a reasonable amount of time.  Maybe my genbigint() function 
> is to blame?  It isn't efficient:
>
> bigint genbigint(int numbits) {
>     bigint tmp;
>     while (numbits --> 0) {
>         tmp <<= 1;
>         tmp += uniform(0, 2);
>     }
>     return tmp;
> }

Yes. You would normally get some random string/value only once 
and then apply md5 or better sha512 on it (several times if you 
want to have a more secur hash) to get the right length and then 
get the hex digest and load it into bigint.