The adder consists of several important subunits. The first one is the
propagate/generate generator. In Magic, this subcell is laid out as:
The next subcell is the sum generator. In Magic, this subcell is
The carry generator can be thought of as a single unit, but the equations used
in each bit are radically different. The following shows each equation,
followed by the corresponding Magic implementation. Note that the
carry equations (and thus, their implementations) are progressively more
complex.
