// This file is part of www.nand2tetris.org
// and the book "The Elements of Computing Systems"
// by Nisan and Schocken, MIT Press.
// File name: tools/builtInChips/ALU.hdl
/**
 * ALU (Arithmetic Logic Unit):
 * Computes out = one of the following functions:
 *                0, 1, -1,
 *                x, y, !x, !y, -x, -y,
 *                x + 1, y + 1, x - 1, y - 1,
 *                x + y, x - y, y - x,
 *                x & y, x | y
 * on the 16-bit inputs x, y,
 * according to the input bits zx, nx, zy, ny, f, no.
 * In addition, computes the output bits:
 * zr = (out == 0, 1, 0)
 * ng = (out < 0,  1, 0)
 */
// Implementation: Manipulates the x and y inputs
// and operates on the resulting values, as follows:
// if (zx == 1) sets x = 0        // 16-bit constant
// if (nx == 1) sets x = !x       // bitwise not
// if (zy == 1) sets y = 0        // 16-bit constant
// if (ny == 1) sets y = !y       // bitwise not
// if (f == 1)  sets out = x + y  // integer 2's complement addition
// if (f == 0)  sets out = x & y  // bitwise and
// if (no == 1) sets out = !out   // bitwise not

CHIP ALU {

    IN  // 16-bit inputs:
        x[16], y[16],
        // Control bits:
        zx, // Zero the x input
        nx, // Negate the x input
        zy, // Zero the y input
        ny, // Negate the y input
        f,  // Function code: 1 for add, 0 for and
        no; // Negate the out output

    OUT // 16-bit output
        out[16],

        // ALU output flags
        zr, // 1 if out=0, 0 otherwise
        ng; // 1 if out<0, 0 otherwise

    BUILTIN ALU;
}