From dc6931639fedff7d2fcd264f157ba53956993b69 Mon Sep 17 00:00:00 2001
From: Rekai Musuka <rekai@musuka.dev>
Date: Sat, 29 Jan 2022 23:53:40 -0400
Subject: [PATCH] fix(cpu): don't ignore 11th bit of THUMB BL offset

---
 src/cpu/thumb/format19.zig | 4 ++--
 1 file changed, 2 insertions(+), 2 deletions(-)

diff --git a/src/cpu/thumb/format19.zig b/src/cpu/thumb/format19.zig
index 86efb03..4fc5513 100644
--- a/src/cpu/thumb/format19.zig
+++ b/src/cpu/thumb/format19.zig
@@ -9,7 +9,7 @@ pub fn format19(comptime is_low: bool) InstrFn {
     return struct {
         fn inner(cpu: *Arm7tdmi, _: *Bus, opcode: u16) void {
             // BL
-            const offset = opcode & 0x3FF;
+            const offset = opcode & 0x7FF;
 
             if (is_low) {
                 // Instruction 2
@@ -19,7 +19,7 @@ pub fn format19(comptime is_low: bool) InstrFn {
                 cpu.r[14] = old_pc | 1;
             } else {
                 // Instruction 1
-                cpu.r[14] = (cpu.r[15] + 2) + (u32SignExtend(11, @as(u32, offset)) << 12);
+                cpu.r[14] = (cpu.r[15] + 2) +% (u32SignExtend(11, @as(u32, offset)) << 12);
             }
         }
     }.inner;