From d6e645cae7d4a5ebb0451d790c7546c3f2538b6f Mon Sep 17 00:00:00 2001
From: Jared Burce <jaredr@gmail.com>
Date: Thu, 18 Mar 2021 01:43:22 -0700
Subject: [PATCH] emu: use wrapping_add in displacement address as operand can
 be neg

---
 src/emu/i8088.rs | 12 ++++++++----
 1 file changed, 8 insertions(+), 4 deletions(-)

diff --git a/src/emu/i8088.rs b/src/emu/i8088.rs
index 9cd199d..d208b68 100644
--- a/src/emu/i8088.rs
+++ b/src/emu/i8088.rs
@@ -133,19 +133,23 @@ macro_rules! step {
   (@displace8=($reg1:ident $(+ $reg2:ident)? ) $cookie:tt, $cpu:expr, $bus:expr,
                                                ($segment:ident, $repeat:ident, $prefix_loop:lifetime),
                                                $modrm:tt) => { {
-    let d8 = i8088::next_ip($cpu.cs.get(), &mut $cpu.ip, $bus);
+    let rel8 = i8088::next_ip($cpu.cs.get(), &mut $cpu.ip, $bus) as i8 as u16;
     step!(@arg $cookie, &mut FarPtr { bus: $bus,
                                       segment: $segment.unwrap(),
-                                      offset: $cpu.$reg1.get() $(+ $cpu.$reg2.get())? + d8 as u16 })
+                                      offset: ($cpu.$reg1.get() $(+ $cpu.$reg2.get())?)
+                                                .wrapping_add(rel8)
+    })
   } };
 
   (@displace16=($reg1:ident $(+ $reg2:ident)? ) $cookie:tt, $cpu:expr, $bus:expr,
                                                 ($segment:ident, $repeat:ident, $prefix_loop:lifetime),
                                                 $modrm:tt) => { {
-    let d16 = i8088::next_ip16($cpu.cs.get(), &mut $cpu.ip, $bus);
+    let rel16 = i8088::next_ip16($cpu.cs.get(), &mut $cpu.ip, $bus);
     step!(@arg $cookie, &mut FarPtr { bus: $bus,
                                       segment: $segment.unwrap(),
-                                      offset: $cpu.$reg1.get() $(+ $cpu.$reg2.get())? + d16 })
+                                      offset: ($cpu.$reg1.get() $(+ $cpu.$reg2.get())?)
+                                                .wrapping_add(rel16)
+    })
   } };
 
   (@flags $cookie:tt, $cpu:expr, $bus:expr, $prefix:tt, $modrm:tt) => {