From 22e0b42305a7413cb85614b1f1d0fa9725ba6980 Mon Sep 17 00:00:00 2001
From: Sean O'Connor <sean@soconnor.dev>
Date: Wed, 3 Sep 2025 10:18:19 -0400
Subject: [PATCH] Update ALU comments

---
 02/ALU.hdl | 4 ++++
 1 file changed, 4 insertions(+)

diff --git a/02/ALU.hdl b/02/ALU.hdl
index 7525c19..9e2635c 100644
--- a/02/ALU.hdl
+++ b/02/ALU.hdl
@@ -66,9 +66,13 @@ CHIP ALU {
     Mux16(a=fout, b=notfout, sel=no, out=out, out[0..7]=outLow, out[8..15]=outHigh, out[15]=sign);
 
     // compute zr (zero flag)
+    // check if any bits in low 8 are set
     Or8Way(in=outLow, out=tmp1);
+    // check if any bits in high 8 are set
     Or8Way(in=outHigh, out=tmp2);
+    // combine both halves (true if any bit is set)
     Or(a=tmp1, b=tmp2, out=notzr);
+    // zr = true if no bits are set (output is zero)
     Not(in=notzr, out=zr);
 
     // compute ng (negative flag)