CLK/InstructionSets/x86/Status.hpp

//
//  Status.hpp
//  Clock Signal
//
//  Created by Thomas Harte on 05/10/2023.
//  Copyright © 2023 Thomas Harte. All rights reserved.
//

#ifndef InstructionSets_x86_Status_hpp
#define InstructionSets_x86_Status_hpp

#include "../../Numeric/Carry.hpp"

namespace InstructionSet::x86 {

namespace ConditionCode {

//
// Standard flags.
//

static constexpr uint32_t Carry				= 1 << 0;
static constexpr uint32_t Parity			= 1 << 2;
static constexpr uint32_t AuxiliaryCarry	= 1 << 4;
static constexpr uint32_t Zero				= 1 << 6;
static constexpr uint32_t Sign				= 1 << 7;
static constexpr uint32_t Trap				= 1 << 8;
static constexpr uint32_t Interrupt			= 1 << 9;
static constexpr uint32_t Direction			= 1 << 10;
static constexpr uint32_t Overflow			= 1 << 11;

//
// 80286+ additions.
//

static constexpr uint32_t IOPrivilege		= (1 << 12) | (1 << 13);
static constexpr uint32_t NestedTask		= 1 << 14;

//
// 16-bit protected mode flags.
//

static constexpr uint32_t ProtectionEnable				= 1 << 16;
static constexpr uint32_t MonitorProcessorExtension		= 1 << 17;
static constexpr uint32_t ProcessorExtensionExtension	= 1 << 18;
static constexpr uint32_t TaskSwitch					= 1 << 19;

//
// 32-bit protected mode flags.
//

static constexpr uint32_t Resume			= 1 << 16;
static constexpr uint32_t VirtualMode		= 1 << 17;

}

enum class Flag {
	Carry,
	AuxiliaryCarry,
	Sign,
	Overflow,
	Trap,
	Interrupt,
	Direction,
	Zero,
	ParityOdd
};

enum class Condition {
	Overflow,
	Below,
	Zero,
	BelowOrEqual,
	Sign,
	ParityOdd,
	Less,
	LessOrEqual
};

class Status {
	public:
		using FlagT = uint32_t;

		// Flag getters.
		template <Flag flag> bool flag() {
			switch(flag) {
				case Flag::Carry:			return carry;
				case Flag::AuxiliaryCarry:	return auxiliary_carry;
				case Flag::Sign:			return sign;
				case Flag::Overflow:		return overflow;
				case Flag::Trap:			return trap;
				case Flag::Interrupt:		return interrupt;
				case Flag::Direction:		return direction;
				case Flag::Zero:			return !zero;
				case Flag::ParityOdd:		return not_parity_bit();
			}
		}

		// Condition evaluation.
		template <Condition test> bool condition() {
			switch(test) {
				case Condition::Overflow:		return flag<Flag::Overflow>();
				case Condition::Below:			return flag<Flag::Carry>();
				case Condition::Zero:			return flag<Flag::Zero>();
				case Condition::BelowOrEqual:	return flag<Flag::Zero>() || flag<Flag::Carry>();
				case Condition::Sign:			return flag<Flag::Sign>();
				case Condition::ParityOdd:		return flag<Flag::ParityOdd>();
				case Condition::Less:			return flag<Flag::Sign>() != flag<Flag::Overflow>();
				case Condition::LessOrEqual:	return flag<Flag::Zero>() || flag<Flag::Sign>() != flag<Flag::Overflow>();
			}
		}

		// Convenience setters.

		/// Sets all of @c flags as a function of @c value:
		/// • Flag::Zero: sets the zero flag if @c value is zero;
		/// • Flag::Sign: sets the sign flag if the top bit of @c value is one;
		/// • Flag::ParityOdd: sets parity based on the low 8 bits of @c value;
		/// • Flag::Carry: sets carry if @c value is non-zero;
		/// • Flag::AuxiliaryCarry: sets auxiliary carry if @c value is non-zero;
		/// • Flag::Overflow: sets overflow if @c value is non-zero;
		/// • Flag::Interrupt: sets interrupt if @c value is non-zero;
		/// • Flag::Trap: sets interrupt if @c value is non-zero;
		/// • Flag::Direction: sets direction if @c value is non-zero.
		template <typename IntT, Flag... flags> void set_from(IntT value) {
			for(const auto flag: {flags...}) {
				switch(flag) {
					default: break;
					case Flag::Zero:			zero = value;								break;
					case Flag::Sign:			sign = value & Numeric::top_bit<IntT>();	break;
					case Flag::ParityOdd:		parity = value;								break;
					case Flag::Carry:			carry = value;								break;
					case Flag::AuxiliaryCarry:	auxiliary_carry = value;					break;
					case Flag::Overflow:		overflow = value;							break;
					case Flag::Interrupt:		interrupt = value;							break;
					case Flag::Trap:			trap = value;								break;
					case Flag::Direction:		direction = value;							break;
				}
			}
		}
		template <Flag... flags> void set_from(FlagT value) {
			set_from<FlagT, flags...>(value);
		}

		template <typename IntT> IntT carry_bit() const { return carry ? 1 : 0; }
		bool not_parity_bit() const {
			// x86 parity always considers the lowest 8-bits only.
			auto result = static_cast<uint8_t>(parity);
			result ^= result >> 4;
			result ^= result >> 2;
			result ^= result >> 1;
			return result & 1;
		}

		// Complete value get and set.
		void set(uint16_t value) {
			carry = value & ConditionCode::Carry;
			auxiliary_carry = value & ConditionCode::AuxiliaryCarry;
			sign = value & ConditionCode::Sign;
			overflow = value & ConditionCode::Overflow;
			trap = value & ConditionCode::Trap;
			interrupt = value & ConditionCode::Interrupt;
			direction = value & ConditionCode::Direction;

			zero = (~value) & ConditionCode::Zero;

			parity = (~value) & ConditionCode::Parity;
		}

		uint16_t get() const {
			return
				0xf002 |

				(carry ? ConditionCode::Carry : 0) |
				(auxiliary_carry ? ConditionCode::AuxiliaryCarry : 0) |
				(sign ? ConditionCode::Sign : 0) |
				(overflow ? ConditionCode::Overflow : 0) |
				(trap ? ConditionCode::Trap : 0) |
				(interrupt ? ConditionCode::Interrupt : 0) |
				(direction ? ConditionCode::Direction : 0) |

				(zero ? 0 : ConditionCode::Zero) |

				(not_parity_bit() ? 0 : ConditionCode::Parity);
		}

		bool operator ==(const Status &rhs) const {
			return get() == rhs.get();
		}

	private:
		// Non-zero => set; zero => unset.
		uint32_t carry;
		uint32_t auxiliary_carry;
		uint32_t sign;
		uint32_t overflow;
		uint32_t trap;
		uint32_t interrupt;
		uint32_t direction;

		// Zero => set; non-zero => unset.
		uint32_t zero;

		// Odd number of bits => set; even => unset.
		uint32_t parity;
};

}

#endif /* InstructionSets_x86_Status_hpp */