FullAdder [ BuiltIn ] Design Type

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FullAdder [ BuiltIn ] Design Type

rjrotheryjr
Everyone,

I read that the Kogge–Stone adder is the fastest.

Does anyone know the BuiltIn FullAdder's design type?

Best,
Richard
 
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Re: FullAdder [ BuiltIn ] Design Type

ybakos
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.
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Re: FullAdder [ BuiltIn ] Design Type

cadet1620
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In reply to this post by rjrotheryjr
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

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Re: FullAdder [ BuiltIn ] Design Type

rjrotheryjr
In reply to this post by ybakos
Thank you Yong.

After reviewing Mark's response and the Java source,
you're correct it does not adhere to any specific design.
The java source is the following:

package builtInChips;

import Hack.Gates.BuiltInGate;

/**
 * A FullAdder.
 * s returns the LSB of the sum of the three bits a,b and c.
 * cout returns the carry bit.
 */
public class FullAdder extends BuiltInGate {

    protected void reCompute() {
        short a = inputPins[0].get();
        short b = inputPins[1].get();
        short c = inputPins[2].get();
        short sum = (short)(a + b + c);
        outputPins[0].set((short)(sum % 2));
        outputPins[1].set((short)(sum / 2));
    }
}

Best,
Richard
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Re: FullAdder [ BuiltIn ] Design Type

rjrotheryjr
In reply to this post by cadet1620
Thanks for the information Mark.

You are correct the Java source is similar to the code you previously posted.
It makes sense to use each user's CPU hardware architecture for the [ BuiltIn ] gates/chips.

If I successfully write a Kogge-Stone implementation, I will certainly post the HDL.


Best,
Richard
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Re: FullAdder [ BuiltIn ] Design Type

rjrotheryjr
In reply to this post by cadet1620
Hi Mark,

I have added a 16-bit Kogge-Stone Parallel Prefix Adder to the forum at:

Kogge-Stone 16-bit Parallel Prefix Adder

I also included an image and a .circ file.
The HDL successfully tests on my platform.

Best,
Richard
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