Attempt VERR, VERW.

Without complete success; IBM's third invocation (which I think is a VERR) doesn't give the result that BIOS is looking for.

InstructionSets/x86/Descriptors.hpp

@@ -38,6 +38,10 @@ enum class DescriptorType {
 	Invalid,
 };
 
+constexpr bool is_data_or_code(const DescriptorType type) {
+	return type <= DescriptorType::Stack;
+}
+
 enum DescriptorTypeFlag: uint8_t {
 	Accessed	= 1 << 0,
 	Busy		= 1 << 1,

InstructionSets/x86/Implementation/LoadStore.hpp

@@ -252,4 +252,20 @@ void str(
 	destination = context.registers.task_state();
 }
 
+template <typename ContextT>
+void verr(
+	read_t<uint16_t> source,
+	ContextT &context
+) {
+	context.flags.template set_from<Flag::Zero>(!context.segments.template verify<false>(source));
+}
+
+template <typename ContextT>
+void verw(
+	read_t<uint16_t> source,
+	ContextT &context
+) {
+	context.flags.template set_from<Flag::Zero>(!context.segments.template verify<true>(source));
+}
+
 }

InstructionSets/x86/Implementation/PerformImplementation.hpp

@@ -605,13 +605,33 @@ template <
 			}
 		break;
 
+		case Operation::VERR:
+			if constexpr (ContextT::model >= Model::i80286 && std::is_same_v<IntT, uint16_t>) {
+				if(is_real(context.cpu_control.mode())) {
+					throw Exception::exception<Vector::InvalidOpcode>();
+					return;
+				}
+				Primitive::verr(source_r(), context);
+			} else {
+				assert(false);
+			}
+		break;
+		case Operation::VERW:
+			if constexpr (ContextT::model >= Model::i80286 && std::is_same_v<IntT, uint16_t>) {
+				if(is_real(context.cpu_control.mode())) {
+					throw Exception::exception<Vector::InvalidOpcode>();
+					return;
+				}
+				Primitive::verw(source_r(), context);
+			} else {
+				assert(false);
+			}
+		break;
+
 		// TODO to reach a full 80286:
 		//
 		//	LAR
-		//	VERR
-		//	VERW
 		//	LSL
-		//	STR
 		//	LOADALL
 	}
 

Machines/PCCompatible/Segments.hpp

@@ -32,6 +32,30 @@ public:
 	using Mode = InstructionSet::x86::Mode;
 	using Source = InstructionSet::x86::Source;
 
+	template <bool for_read>
+	bool verify(const uint16_t value) {
+		try {
+			const auto incoming = descriptor(value);
+			const auto description = incoming.description();
+
+			if(!is_data_or_code(description.type)) {
+				return false;
+			}
+
+			if(for_read && !description.readable) {
+				return false;
+			} else if(!description.writeable) {
+				return false;
+			}
+
+			// TODO: privilege level?
+
+			return true;
+		} catch (const InstructionSet::x86::Exception &e) {
+			return false;
+		}
+	}
+
 	void preauthorise(
 		const Source segment,
 		const uint16_t value