From 1b9ab1f1d729eb0d30c5fbeec486acd5068297fb Mon Sep 17 00:00:00 2001
From: Rekai Musuka <rekai@musuka.dev>
Date: Sat, 5 Feb 2022 23:08:47 -0400
Subject: [PATCH] fix: implement the same LDRSH logic as THUMB LDRSH

---
 src/cpu/arm/half_signed_data_transfer.zig | 8 +++++++-
 1 file changed, 7 insertions(+), 1 deletion(-)

diff --git a/src/cpu/arm/half_signed_data_transfer.zig b/src/cpu/arm/half_signed_data_transfer.zig
index ba97d62..e30570a 100644
--- a/src/cpu/arm/half_signed_data_transfer.zig
+++ b/src/cpu/arm/half_signed_data_transfer.zig
@@ -45,7 +45,13 @@ pub fn halfAndSignedDataTransfer(comptime P: bool, comptime U: bool, comptime I:
                     },
                     0b11 => {
                         // LDRSH
-                        result = util.u32SignExtend(16, bus.read16(address & 0xFFFF_FFFE));
+                        const value = if (address & 1 == 1) blk: {
+                            break :blk util.u32SignExtend(8, bus.read8(address));
+                        } else blk: {
+                            break :blk util.u32SignExtend(16, bus.read16(address));
+                        };
+
+                        result = std.math.rotr(u32, value, 8 * (address & 1));
                     },
                     0b00 => unreachable, // SWP
                 }