nand2tetris/projects/02/FullAdder.hdl

// This file is part of www.nand2tetris.org
// and the book "The Elements of Computing Systems"
// by Nisan and Schocken, MIT Press.
// File name: projects/02/FullAdder.hdl

/**
 * Computes the sum of three bits.
 */

CHIP FullAdder {
    IN a, b, c;  // 1-bit inputs
    OUT sum,     // Right bit of a + b + c
        carry;   // Left bit of a + b + c

    PARTS:
    HalfAdder(a=a, b=b, sum=h1, carry=c1);
    HalfAdder(a=h1, b=c, sum=h2, carry=c2);

    Xor(a=a, b=b, out=axb);
    And(a=axb, b=c, out=notout);

    Or(a=h1, b=h2, out=sum1);

    Xor(a=sum1, b=notout, out=sum);

    Or(a=c1, b=c2, out=carry);
}