extract_fa - find and extract full/half adders

yosys> help extract_fa
extract_fa [options] [selection]
This pass extracts full/half adders from a gate-level design.
-fa, -ha
Enable cell types (fa=full adder, ha=half adder)
All types are enabled if none of this options is used
-d <int>
Set maximum depth for extracted logic cones (default=20)
-b <int>
Set maximum breadth for extracted logic cones (default=6)
Verbose output