From df95e25eaa618ae83d0ff0c3d6a2d6a22821f5ec Mon Sep 17 00:00:00 2001
From: Andreas Kling <kling@serenityos.org>
Date: Sun, 12 Jul 2020 00:36:07 +0200
Subject: [PATCH] UserspaceEmulator: Implement the NEG instruction

Per the Intel manuals, NEG is equivalent to subtracting a value from 0.
---
 DevTools/UserspaceEmulator/SoftCPU.cpp | 19 ++++++++++++++++---
 1 file changed, 16 insertions(+), 3 deletions(-)

diff --git a/DevTools/UserspaceEmulator/SoftCPU.cpp b/DevTools/UserspaceEmulator/SoftCPU.cpp
index 9508ec1f95..1547b26239 100644
--- a/DevTools/UserspaceEmulator/SoftCPU.cpp
+++ b/DevTools/UserspaceEmulator/SoftCPU.cpp
@@ -998,9 +998,22 @@ void SoftCPU::MOV_seg_RM32(const X86::Instruction&) { TODO(); }
 void SoftCPU::MUL_RM16(const X86::Instruction&) { TODO(); }
 void SoftCPU::MUL_RM32(const X86::Instruction&) { TODO(); }
 void SoftCPU::MUL_RM8(const X86::Instruction&) { TODO(); }
-void SoftCPU::NEG_RM16(const X86::Instruction&) { TODO(); }
-void SoftCPU::NEG_RM32(const X86::Instruction&) { TODO(); }
-void SoftCPU::NEG_RM8(const X86::Instruction&) { TODO(); }
+
+void SoftCPU::NEG_RM16(const X86::Instruction& insn)
+{
+    insn.modrm().write16(*this, insn, op_sub<u16>(*this, 0, insn.modrm().read16(*this, insn)));
+}
+
+void SoftCPU::NEG_RM32(const X86::Instruction& insn)
+{
+    insn.modrm().write32(*this, insn, op_sub<u32>(*this, 0, insn.modrm().read32(*this, insn)));
+}
+
+void SoftCPU::NEG_RM8(const X86::Instruction& insn)
+{
+    insn.modrm().write8(*this, insn, op_sub<u8>(*this, 0, insn.modrm().read8(*this, insn)));
+}
+
 void SoftCPU::NOP(const X86::Instruction&) { TODO(); }
 void SoftCPU::NOT_RM16(const X86::Instruction&) { TODO(); }
 void SoftCPU::NOT_RM32(const X86::Instruction&) { TODO(); }