From d897c2fdcc06dfe7185645309627539214914575 Mon Sep 17 00:00:00 2001
From: Rekai Musuka <rekai@musuka.dev>
Date: Sat, 12 Feb 2022 03:23:55 -0400
Subject: [PATCH] fix: don't mask away MSB in THUMB.5 add

---
 src/cpu/thumb/processing_branch.zig | 6 +++++-
 1 file changed, 5 insertions(+), 1 deletion(-)

diff --git a/src/cpu/thumb/processing_branch.zig b/src/cpu/thumb/processing_branch.zig
index 52faf15..0540526 100644
--- a/src/cpu/thumb/processing_branch.zig
+++ b/src/cpu/thumb/processing_branch.zig
@@ -15,7 +15,11 @@ pub fn format5(comptime op: u2, comptime h1: u1, comptime h2: u1) InstrFn {
             const dst = if (dst_idx == 0xF) (cpu.r[dst_idx] + 2) & 0xFFFF_FFFE else cpu.r[dst_idx];
 
             switch (op) {
-                0b00 => cpu.r[dst_idx] = add(false, cpu, dst, src) & if (dst_idx == 0xF) 0xFFFF_FFFC else @as(u32, 0xFFF_FFFF), // ADD
+                0b00 => {
+                    // ADD
+                    const sum = add(false, cpu, dst, src);
+                    cpu.r[dst_idx] = if (dst_idx == 0xF) sum & 0xFFFF_FFFC else sum;
+                },
                 0b01 => cmp(cpu, dst, src), // CMP
                 0b10 => {
                     // MOV