my $prng;
if ( -f '/dev/random' ) {
   $prng = sub { get_rand_from_file('/dev/random', shift) };
}
elsif ( ## Find out if RtlGenRandom works ## ) {
   $prng = \&rtlGenRandom_rand;
}
else {
   require Crypt::Random::ISAAC;
   $prng = \&Crypt::Random::ISAAC::rand;
}