From 8e669a32a3f76069416a002d9f622d63552cfe70 Mon Sep 17 00:00:00 2001
From: Thomas Harte <thomas.harte@gmail.com>
Date: Mon, 7 Mar 2022 16:34:56 -0500
Subject: [PATCH] Take a stab at group 8.

---
 InstructionSets/x86/Decoder.cpp | 23 +++++++++++++++++++----
 InstructionSets/x86/Decoder.hpp |  3 ++-
 2 files changed, 21 insertions(+), 5 deletions(-)

diff --git a/InstructionSets/x86/Decoder.cpp b/InstructionSets/x86/Decoder.cpp
index e16668563..521f1c4dd 100644
--- a/InstructionSets/x86/Decoder.cpp
+++ b/InstructionSets/x86/Decoder.cpp
@@ -524,10 +524,10 @@ std::pair<int, typename Decoder<model>::InstructionT> Decoder<model>::decode(con
 				RequiresMin(i80386);
 				MemRegReg(MOVZX, Reg_MemReg, DataSize::Word);
 			break;
-			// TODO: 0xba: Grp8 Ev, Ib
-			case 0xbb: RequiresMin(i80386);	MemRegReg(BTC, MemReg_Reg, data_size_);	break;
-			case 0xbc: RequiresMin(i80386);	MemRegReg(BSF, MemReg_Reg, data_size_);	break;
-			case 0xbd: RequiresMin(i80386);	MemRegReg(BSR, MemReg_Reg, data_size_);	break;
+			case 0xba: RequiresMin(i80386);	MemRegReg(Invalid, MemRegBT_to_BTC, data_size_);	break;
+			case 0xbb: RequiresMin(i80386);	MemRegReg(BTC, MemReg_Reg, data_size_);				break;
+			case 0xbc: RequiresMin(i80386);	MemRegReg(BSF, MemReg_Reg, data_size_);				break;
+			case 0xbd: RequiresMin(i80386);	MemRegReg(BSR, MemReg_Reg, data_size_);				break;
 			case 0xbe:
 				RequiresMin(i80386);
 				MemRegReg(MOVSX, Reg_MemReg, DataSize::Byte);
@@ -776,6 +776,21 @@ std::pair<int, typename Decoder<model>::InstructionT> Decoder<model>::decode(con
 				}
 			break;
 
+			case ModRegRMFormat::MemRegBT_to_BTC:
+				destination_ = memreg;
+				source_ = Source::Immediate;
+				operand_size_ = DataSize::Byte;
+
+				switch(reg) {
+					default:	undefined();
+
+					case 4:		operation_ = Operation::BT;		break;
+					case 5:		operation_ = Operation::BTS;	break;
+					case 6:		operation_ = Operation::BTR;	break;
+					case 7:		operation_ = Operation::BTC;	break;
+				}
+			break;
+
 			default: assert(false);
 		}
 
diff --git a/InstructionSets/x86/Decoder.hpp b/InstructionSets/x86/Decoder.hpp
index 6f0c4a6aa..6c837df2a 100644
--- a/InstructionSets/x86/Decoder.hpp
+++ b/InstructionSets/x86/Decoder.hpp
@@ -156,7 +156,8 @@ template <Model model> class Decoder {
 			//	'Group 8'
 			//
 
-			// TODO.
+			// Parse for mode and register/memory field, populating destination,
+			// and prepare to read a single byte as source.
 			MemRegBT_to_BTC,
 		} modregrm_format_ = ModRegRMFormat::MemReg_Reg;