// 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/01/DMux4Way.hdl

/**
 * 4-way demultiplexor:
 * {a, b, c, d} = {in, 0, 0, 0} if sel == 00
 *                {0, in, 0, 0} if sel == 01
 *                {0, 0, in, 0} if sel == 10
 *                {0, 0, 0, in} if sel == 11
 */

CHIP DMux4Way {
    IN in, sel[2];
    OUT a, b, c, d;

    PARTS:

    /**
     * Demultiplexor:
     * {x, y} = {in, 0} if sel[0] == 0
     *          {0, in} if sel[0] == 1
     */
    DMux(in=in, sel=sel[0], a=x, b=y);
    // Now we can copy x,y to abcd as {x|0,y|0,x|0,y|0}
    // depending on sel[1]

    // sel| 00 | 01 || 10 | 11
    //S[1]|    0    ||    1
    //----|----|----||----|---
    // x  | in | 0  || in | 0
    // y  | 0  | in || 0  | in
    //----|----|----||----|---
    // a  | in | 0  || 0  | 0
    // b  | 0  | in || 0  | 0
    // c  | 0  | 0  || in | 0
    // d  | 0  | 0  || 0  | in
    Mux(a=x, b=false, sel=sel[1], out=a);
    Mux(a=y, b=false, sel=sel[1], out=b);
    Mux(a=false, b=x, sel=sel[1], out=c);
    Mux(a=false, b=y, sel=sel[1], out=d);
}