From 0b71b99b792e050941f79555571678c0ad88aa72 Mon Sep 17 00:00:00 2001
From: MichaelValwin <macm241192@gmail.com>
Date: Fri, 6 Sep 2024 14:37:24 +0200
Subject: [PATCH] Fix a instruction from overflowing indexReg

---
 src/cpu.ts | 7 ++++---
 1 file changed, 4 insertions(+), 3 deletions(-)

diff --git a/src/cpu.ts b/src/cpu.ts
index cd505cd..02e3428 100644
--- a/src/cpu.ts
+++ b/src/cpu.ts
@@ -222,7 +222,7 @@ class CPU {
 			case 0x8: {
 				if(nib4 == 0x0) {
 					// 8XY0
-					// Vx |= Vy
+					// Vx = Vy
 					this.regs[nib2] = this.regs[nib3];
 					this.incrementPC();
 				}else if(nib4 == 0x1) {
@@ -307,7 +307,7 @@ class CPU {
 				break;
 			case 0xB:{
 				// BNNN
-				// Jumps to the address NNN plus V0
+				// Jumps to the address (NNN + V0)
 				let address = opcode & 0x0FFF;
 				this.pc = this.regs[0] + address;
 				}
@@ -406,12 +406,13 @@ class CPU {
 					// I += Vx
 					// Adds VX to I. VF is not affected
 					this.indexReg += this.regs[nib2];
+					this.indexReg = this.indexReg & 0xFFFF;
 					this.incrementPC();
 				}else if(secondOpcode == 0x29) {
 					// FX29
 					// I = sprite_addr[Vx]
 					// Sets I to the location of the sprite for the character in VX
-					this.indexReg = this.regs[nib2] * 0x5; // ??
+					this.indexReg = this.regs[nib2] * 0x5;
 					this.incrementPC();
 				}else if(secondOpcode == 0x33) {
 					// FX33