CHIP ZN {
    IN  in[16], z, n;
    OUT out[16];

    PARTS:
    // first decide whether to zero input
    Mux16(a=in, b=false, sel=z, out=zout);

    // then decide whether to negate possibly zeroed input
    Not16(in=zout, out=notzout);
    Mux16(a=zout, b=notzout, sel=n, out=out);
}