The output is the inverted carry of carry inputs
a and c
and the carry of input b.
The stage efforts for pin b
is 1.6, 1.9 and 2.4 for the x05,
x1 and x2 drive strengths respectively.
The cells here use a P/N ratio of about 2.
z:((a*b')+(a*c)+(b'*c))'
cell width
power
Generic 0.13um typical timing (ps & ps/fF),
pin c.