Re: FullAdder [ BuiltIn ] Design Type

Posted by cadet1620 on
URL: http://nand2tetris-questions-and-answers-forum.52.s1.nabble.com/FullAdder-BuiltIn-Design-Type-tp4027554p4027560.html

rjrotheryjr wrote

Does anyone know the BuiltIn FullAdder's design type?

ybakos wrote

The one we build in HDL is a ripple-carry adder, for its simplicity.

The built-in is software-driven, and because of this abstraction I don't believe it adheres to a specific adder design.

As Yong wrote, the built-in parts are software (written in Java). Assuming that the Java code does something like io_pins.out = io_pins.a + io_pins.b, it will be using your computer's CPU's addition hardware.

There are some forum posts on faster adder architectures:
    Carry Look-Ahead Adder
    Carry Select Adder
    Carry Bypass Adder

If I remember correctly, Kogge–Stone is a space/time trade-off that optimizes carry-lookahead adders for time.

If you implement it in HDL, please post it to the forum!

--Mark