Re: Carry Select Adder

Posted by cadet1620 on Mar 05, 2017; 12:14am
URL: http://nand2tetris-questions-and-answers-forum.52.s1.nabble.com/Carry-Select-Adder-tp4025925p4030819.html

tungsten wrote

Is the Carry Select Adder faster than the CLA? What about the CLA/CSA hybrid you've shared, is it faster than the individual?

If circuit size is no concern, what's the fastest adder one can use?
Also which one is the middle-ground(does best job of balancing circuit size and speed)?

Doing static worst case analysis by hand would be quite arduous.
I think that you'd need to code these in an industrial strength HDL (Verilog or VHDL) and run them on a real simulator to figure that out.

Was planning on swapping in the CLA to speed up my ALU, but I'm willing to use whatever is fastest.

Other than an intellectual exercise, this is moot. Because all of these adders involve many more gates, I expect that they will all run slower in the HardwareSimulator. In any case, there is very little correlation between simulator run time and circuit worst case timing.

[I never had to do any designs that needed fast adders. The few times I needed them I just used 4-bit adder parts with ripple carry between them. IIRC the longest one was 9 bits (3 4-bit parts) for a CRT display row counter.]

--Mark