From f70f5307220d80526bd3f12d86966156f4ec6752 Mon Sep 17 00:00:00 2001
From: Andreas Kling <kling@serenityos.org>
Date: Sat, 18 Jul 2020 00:15:36 +0200
Subject: [PATCH] UserspaceEmulator: Implement the SCASB/SCASW/SCASD
 instructions

---
 DevTools/UserspaceEmulator/SoftCPU.cpp | 28 +++++++++++++++++++++++---
 1 file changed, 25 insertions(+), 3 deletions(-)

diff --git a/DevTools/UserspaceEmulator/SoftCPU.cpp b/DevTools/UserspaceEmulator/SoftCPU.cpp
index 207c878489..7d6f8dfcd6 100644
--- a/DevTools/UserspaceEmulator/SoftCPU.cpp
+++ b/DevTools/UserspaceEmulator/SoftCPU.cpp
@@ -2014,9 +2014,31 @@ static T op_sar(SoftCPU& cpu, T data, u8 steps)
 
 DEFINE_GENERIC_SHIFT_ROTATE_INSN_HANDLERS(SAR, op_sar)
 
-void SoftCPU::SCASB(const X86::Instruction&) { TODO(); }
-void SoftCPU::SCASD(const X86::Instruction&) { TODO(); }
-void SoftCPU::SCASW(const X86::Instruction&) { TODO(); }
+template<typename T>
+ALWAYS_INLINE static void do_scas(SoftCPU& cpu, const X86::Instruction& insn)
+{
+    cpu.do_once_or_repeat<true>(insn, [&] {
+        auto src = cpu.gpr<T>(X86::RegisterAL);
+        auto dest = cpu.read_memory<T>({ cpu.es(), cpu.destination_index(insn.a32()) });
+        op_sub(cpu, dest, src);
+        cpu.step_destination_index(insn.a32(), sizeof(T));
+    });
+}
+
+void SoftCPU::SCASB(const X86::Instruction& insn)
+{
+    do_scas<u8>(*this, insn);
+}
+
+void SoftCPU::SCASD(const X86::Instruction& insn)
+{
+    do_scas<u32>(*this, insn);
+}
+
+void SoftCPU::SCASW(const X86::Instruction& insn)
+{
+    do_scas<u16>(*this, insn);
+}
 
 void SoftCPU::SETcc_RM8(const X86::Instruction& insn)
 {