EightBit/inc/IntelProcessor.h

#pragma once

#include <cstdint>
#include <array>

#include "Bus.h"
#include "LittleEndianProcessor.h"
#include "Register.h"
#include "EventArgs.h"
#include "Signal.h"
#include "EightBitCompilerDefinitions.h"

namespace EightBit {
	class IntelProcessor : public LittleEndianProcessor {
	public:
		struct opcode_decoded_t {

			int x = 0;
			int y = 0;
			int z = 0;
			int p = 0;
			int q = 0;

			opcode_decoded_t() noexcept {}

			opcode_decoded_t(const uint8_t opcode) noexcept {
				x = (opcode & 0b11000000) >> 6;	// 0 - 3
				y = (opcode & 0b00111000) >> 3;	// 0 - 7
				z = (opcode & 0b00000111);		// 0 - 7
				p = (y & 0b110) >> 1;			// 0 - 3
				q = (y & 1);					// 0 - 1
			}
		};

		~IntelProcessor() = default;

		[[nodiscard]] const auto& getDecodedOpcode(const size_t i) const noexcept {
			return m_decodedOpcodes.at(i);
		}

		[[nodiscard]] auto& MEMPTR() noexcept { return m_memptr; }

		[[nodiscard]] auto& SP() noexcept { return m_sp; }

		[[nodiscard]] virtual register16_t& AF() = 0;
		[[nodiscard]] auto& A() { return AF().high; }
		[[nodiscard]] auto& F() { return AF().low; }

		[[nodiscard]] virtual register16_t& BC() = 0;
		[[nodiscard]] auto& B() { return BC().high; }
		[[nodiscard]] auto& C() { return BC().low; }

		[[nodiscard]] virtual register16_t& DE() = 0;
		[[nodiscard]] auto& D() { return DE().high; }
		[[nodiscard]] auto& E() { return DE().low; }

		[[nodiscard]] virtual register16_t& HL() = 0;
		[[nodiscard]] auto& H() { return HL().high; }
		[[nodiscard]] auto& L() { return HL().low; }

		DECLARE_PIN_OUTPUT(HALT)

	protected:
		IntelProcessor(Bus& bus);

		template<class T> [[nodiscard]] static uint8_t adjustSign(uint8_t f, const uint8_t value) {
			return setBit(f, T::SF, value & T::SF);
		}

		template<class T> [[nodiscard]] static uint8_t adjustZero(uint8_t f, const uint8_t value) {
			return clearBit(f, T::ZF, value);
		}

		template<class T> [[nodiscard]] static uint8_t adjustParity(uint8_t f, const uint8_t value) {
			return clearBit(f, T::PF, PARITY(value));
		}

		template<class T> [[nodiscard]] static uint8_t adjustSZ(uint8_t f, const uint8_t value) {
			const auto intermediate = adjustSign<T>(f, value);
			return adjustZero<T>(intermediate, value);
		}

		template<class T> [[nodiscard]] static uint8_t adjustSZP(uint8_t f, const uint8_t value) {
			const auto intermediate = adjustSZ<T>(f, value);
			return adjustParity<T>(intermediate, value);
		}

		template<class T> [[nodiscard]] static uint8_t adjustXY(uint8_t f, const uint8_t value) {
			const auto intermediate = setBit(f, T::XF, value & T::XF);
			return setBit(intermediate, T::YF, value & T::YF);
		}

		template<class T> [[nodiscard]] static uint8_t adjustSZPXY(uint8_t f, const uint8_t value) {
			const auto intermediate = adjustSZP<T>(f, value);
			return adjustXY<T>(intermediate, value);
		}

		template<class T> [[nodiscard]] static uint8_t adjustSZXY(uint8_t f, const uint8_t value) {
			const auto intermediate = adjustSZ<T>(f, value);
			return adjustXY<T>(intermediate, value);
		}

		//

		[[nodiscard]] static constexpr auto buildHalfCarryIndex(const uint8_t before, const uint8_t value, const int calculation) {
			return ((before & 0x88) >> 1) | ((value & 0x88) >> 2) | ((calculation & 0x88) >> 3);
		}

		[[nodiscard]] static auto calculateHalfCarryAdd(const uint8_t before, const uint8_t value, const int calculation) noexcept {
			static std::array<int, 8> halfCarryTableAdd = { { 0, 0, 1, 0, 1, 0, 1, 1} };
			const auto index = buildHalfCarryIndex(before, value, calculation);
			return halfCarryTableAdd.at(index & Mask3);
		}

		[[nodiscard]] static auto calculateHalfCarrySub(const uint8_t before, const uint8_t value, const int calculation) noexcept {
			std::array<int, 8> halfCarryTableSub = { { 0, 1, 1, 1, 0, 0, 0, 1 } };
			const auto index = buildHalfCarryIndex(before, value, calculation);
			return halfCarryTableSub.at(index & Mask3);
		}

		void handleRESET() override;

		void push(uint8_t value) final;
		[[nodiscard]] uint8_t pop() final;

		//

		[[nodiscard]] register16_t getWord() final;
		void setWord(register16_t value) final;

		//

		void restart(const uint8_t address) {
			call(MEMPTR() = { address, 0 });
		}

		auto callConditional(const int condition) {
			MEMPTR() = fetchWord();
			if (condition)
				call(MEMPTR());
			return condition;
		}

		auto jumpConditional(const int condition) {
			MEMPTR() = fetchWord();
			if (condition)
				jump(MEMPTR());
			return condition;
		}

		auto returnConditional(const int condition) {
			if (condition)
				ret();
			return condition;
		}

		void jr(const int8_t offset) noexcept {
			jump(MEMPTR() = PC() + offset);
		}

		auto jrConditional(const int condition) {
			const auto offsetAddress = PC()++;
			if (condition) {
				const auto offset = memoryRead(offsetAddress);
				jr(offset);
			}
			return condition;
		}

		void ret() final;

	private:
		std::array<opcode_decoded_t, 0x100> m_decodedOpcodes;
		register16_t m_sp = Mask16;
		register16_t m_memptr;
	};
}