// This file is part of the materials accompanying the book 

// "The Elements of Computing Systems" by Nisan and Schocken, 

// MIT Press. Book site: www.idc.ac.il/tecs

// File name: projects/02/FullAdder.hdl



/**

 * Full adder. Computes sum, the least significant bit of 

 * a + b + c, and carry, the most significant bit of a + b + c.

 * 

 * The LSB of a + b +c = LSB(a + b) + c

 * The MSB of a + b + c = MSB(a + b), MSB can never be more than 1

 * given that max sum is 1 + 1 + 1 = 11

 */



CHIP FullAdder {



    IN  a, b, c;

    OUT sum,     // LSB of a + b + c

        carry;   // MSB of a + b + c



    PARTS:

    HalfAdder(a=a, b=b, sum=absum, carry=abcarry);

    HalfAdder(a=absum, b=c, sum=sum, carry=abccarry);

    Xor(a=abcarry, b=abccarry, out=carry);

}