
Nvm, I fixed it:
Spoiler for the working ALU design 
// 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/ALU.hdl
/**
* The ALU (Arithmetic Logic Unit).
* Computes one of the following functions:
* x+y, xy, yx, 0, 1, 1, x, y, x, y, !x, !y,
* x+1, y+1, x1, y1, x&y, xy on two 16bit inputs,
* according to 6 input bits denoted zx,nx,zy,ny,f,no.
* In addition, the ALU computes two 1bit outputs:
* if the ALU output == 0, zr is set to 1; otherwise zr is set to 0;
* if the ALU output < 0, ng is set to 1; otherwise ng is set to 0.
*/
// Implementation: the ALU logic manipulates the x and y inputs
// and operates on the resulting values, as follows:
// if (zx == 1) set x = 0 // 16bit constant
// if (nx == 1) set x = !x // bitwise not
// if (zy == 1) set y = 0 // 16bit constant
// if (ny == 1) set y = !y // bitwise not
// if (f == 1) set out = x + y // integer 2's complement addition
// if (f == 0) set out = x & y // bitwise and
// if (no == 1) set out = !out // bitwise not
// if (out == 0) set zr = 1
// if (out < 0) set ng = 1
CHIP ALU {
IN
x[16], y[16], // 16bit inputs
zx, // zero the x input?
nx, // negate the x input?
zy, // zero the y input?
ny, // negate the y input?
f, // compute out = x + y (if 1) or x & y (if 0)
no; // negate the out output?
OUT
out[16], // 16bit output
zr, // 1 if (out == 0), 0 otherwise
ng; // 1 if (out < 0), 0 otherwise
PARTS:
// Put you code here:
//Implement zx
Mux16(a=x, b=false, sel=zx, out=zxx);
//Implement zy
Mux16(a=y, b=false, sel=zy, out=zyy);
//Implement nx
Not16(in = zxx, out = notzxx);
Mux16(a = zxx, b = notzxx, sel = nx, out = zxnxx);
//Implement ny
Not16(in = zyy, out = notzyy);
Mux16(a = zyy, b = notzyy, sel = ny, out = zynyy);
//Implement f
And16(a= zxnxx, b= zynyy, out= andxy);
Add16(a= zxnxx, b= zynyy, out= addxy);
Mux16(a= andxy, b=addxy, sel=f, out= fout);
//Inverse if no and also ng
Not16(in=fout, out=nfout);
Mux16(a=fout, b=nfout, sel=no, out = out, out=finalout, out[15] = ng, out[0..7] = firsthalf,out[8..15] = secondhalf );
//zr
Or8Way(in=firsthalf, out=a);
Or8Way(in=secondhalf, out=b);
Or(a=a, b=b, out=notzr);
Not(in = notzr, out = zr);
}
