From 784bc81a4a8e09341d6858ab8eeb8a1e4768d5ad Mon Sep 17 00:00:00 2001
From: Rekai Musuka <rekai@musuka.dev>
Date: Wed, 2 Feb 2022 18:57:33 -0400
Subject: [PATCH] fix(cpu): account for overflow in THUMB alu MUL

---
 src/cpu/thumb/format4.zig | 3 ++-
 1 file changed, 2 insertions(+), 1 deletion(-)

diff --git a/src/cpu/thumb/format4.zig b/src/cpu/thumb/format4.zig
index 80af863..ee8964a 100644
--- a/src/cpu/thumb/format4.zig
+++ b/src/cpu/thumb/format4.zig
@@ -90,7 +90,8 @@ pub fn format4(comptime op: u4) InstrFn {
                 },
                 0xD => {
                     // MUL
-                    const result = cpu.r[rs] * cpu.r[rd];
+                    const temp = @as(u64, cpu.r[rs]) * @as(u64, cpu.r[rd]);
+                    const result = @truncate(u32, temp);
                     cpu.r[rd] = result;
 
                     cpu.cpsr.n.write(result >> 31 & 1 == 1);