sub blog10 {
    my $bn = shift;

    require Math::BigInt;
    return (ref($bn) ? $bn->copy : Math::BigInt->new($bn))->blog(10);
}

my $bn = 1e12;
my $blog10 = blog10($bn);

print "blog10($bn): $blog10\n";
print "mod($blog10,3): ", $blog10 % 3, "\n";
print "int($blog10): ", int($blog10), "\n";