sub most_significant_ix {
    my $n = shift;
    return if $_[0] == 0;
    return int(log($_[0])/log(2));
}

##</code><code>##

sub most_significant_ix {
    my $n = shift;
    return undef if $n == 0;
    my $bits = 64;
    while (--$bits >= 0) {
        return $bits if (2**$bits) & $n;
    }
}