my $data = 0x00;
bit_on($data, 4);   # enables the offset
my $offsetBits = bit_mask_disjoint(6,5,3,2,1,0);
foreach my $val ( 0..63 ) {
    bit_set_disjoint($data, $offsetBits, $val);      # sets the offset bits without affecting the enable bit
    ...
}
...
my $ctrl = 0x00;            # ctrl is a three-bit register
my $permuteBits = [1,0,2];  # but HW designer and I think of the bits as being in a different order
foreach my $val ( 0..7 ) {
    bit_set_disjoint($ctrl, $permuteBits, $val);    # 0:000; 1:010; 2:100; 3:110; 4:001; 5:011; 6:101; 7:111;
    ...
}