sub inblock-cidr {
  my ($block, $cidr, $target) = @_;
  my $result = 1;
  my $machinebits = (32 - $cidr);
  my $lip1 = 
    unpack("N", pack("c4", split(/\D/, $block,  4)));
  my $lip2 = 
    unpack("N", pack("c4", split(/\D/, $target, 4)));
  $result = 0    
    if (($lip1 >> $machinebits) != ($lip2 >> $machinebits));
  return($result);
} 
sub inblock-mask {
  my ($block, $mask, $target) = @_;
  my $result = 1;
  my $machinebits = 
    unpack("N", pack("c4", split(/\D/, $mask,   4)));
  my $lip1 = 
    unpack("N", pack("c4", split(/\D/, $block,  4)));
  my $lip2 = 
    unpack("N", pack("c4", split(/\D/, $target, 4)));
  $result = 0    
    if (($lip1 & $machinebits) != ($lip2 & $machinebits));
  return($result);
}
&inblock-cidr('10.0.0.0', 8, '10.13.23.42');
&inblock-mask('10.0.0.0', '255.0.0.0', '10.13.23.42');