//
//  PerformImplementation.hpp
//  Clock Signal
//
//  Created by Thomas Harte on 28/04/2022.
//  Copyright © 2022 Thomas Harte. All rights reserved.
//

#ifndef InstructionSets_M68k_PerformImplementation_h
#define InstructionSets_M68k_PerformImplementation_h

#include "../ExceptionVectors.hpp"

#include <cassert>
#include <cmath>

namespace InstructionSet {
namespace M68k {

#define u_extend16(x)	uint32_t(int16_t(x))
#define s_extend16(x)	int32_t(int16_t(x))

namespace Primitive {

/// @returns An int of type @c IntT with only the most-significant bit set.
template <typename IntT> constexpr IntT top_bit() {
	static_assert(!std::numeric_limits<IntT>::is_signed);
	constexpr IntT max = std::numeric_limits<IntT>::max();
	return max - (max >> 1);
}

/// @returns The number of bits in @c IntT.
template <typename IntT> constexpr int bit_count() {
	return sizeof(IntT) * 8;
}

/// @returns An int with the top bit indicating whether overflow occurred when @c source and @c destination
/// were either added (if @c is_add is true) or subtracted (if @c is_add is false) and the result was @c result.
/// All other bits will be clear.
template <bool is_add, typename IntT>
static Status::FlagT overflow(IntT source, IntT destination, IntT result) {
	const IntT output_changed = result ^ destination;
	const IntT input_differed = source ^ destination;

	if constexpr (is_add) {
		return top_bit<IntT>() & output_changed & ~input_differed;
	} else {
		return top_bit<IntT>() & output_changed & input_differed;
	}
}

/// Performs an add or subtract (as per @c is_add) between @c source and @c destination,
/// updating @c status. @c is_extend indicates whether this is an extend operation (e.g. ADDX)
/// or a plain one (e.g. ADD).
template <bool is_add, bool is_extend, typename IntT>
static void add_sub(IntT source, IntT &destination, Status &status) {
	static_assert(!std::numeric_limits<IntT>::is_signed);

	const IntT extend = (is_extend && status.extend_flag) ? 1 : 0;
	const IntT result = is_add ?
		(destination + source + extend) :
		(destination - source - extend);

	// Extend operations can reset the zero flag only; non-extend operations
	// can either set it or reset it. Which in the reverse-logic world of
	// zero_result means ORing or storing.
	if constexpr (is_extend) {
		status.zero_result |= Status::FlagT(result);
	} else {
		status.zero_result = Status::FlagT(result);
	}
	status.extend_flag =
	status.carry_flag = is_add ? result < destination : result > destination;
	status.negative_flag = Status::FlagT(result & top_bit<IntT>());
	status.overflow_flag = overflow<is_add>(source, destination, result);
	destination = result;
}

/// Performs a compare of @c source to @c destination, setting zero, carry, negative and overflow flags.
template <typename IntT>
static void compare(IntT source, IntT destination, Status &status) {
	const IntT result = destination - source;
	status.zero_result = result;
	status.carry_flag = result > destination;
	status.negative_flag = result & top_bit<IntT>();
	status.overflow_flag = Primitive::overflow<false>(source, destination, result);
}

/// @returns the name of the bit to be used as a mask for BCLR, BCHG, BSET or BTST for
/// @c instruction given @c source.
inline uint32_t mask_bit(const Preinstruction &instruction, uint32_t source) {
	return source & (instruction.mode<1>() == AddressingMode::DataRegisterDirect ? 31 : 7);
}

/// Performs a BCLR, BCHG or BSET as specified by @c operation and described by @c instruction, @c source and @c destination, updating @c destination and @c status.
/// Also makes an appropriate notification to the @c flow_controller.
template <Operation operation, typename FlowController>
void bit_manipulate(const Preinstruction &instruction, uint32_t source, uint32_t &destination, Status &status, FlowController &flow_controller) {
	static_assert(
		operation == Operation::BCLR ||
		operation == Operation::BCHG ||
		operation == Operation::BSET);

	const auto bit = mask_bit(instruction, source);
	status.zero_result = destination & (1 << bit);
	switch(operation) {
		case Operation::BCLR:	destination &= ~(1 << bit);	break;
		case Operation::BCHG:	destination ^= (1 << bit);	break;
		case Operation::BSET:	destination |= (1 << bit);	break;
	}
	flow_controller.did_bit_op(int(bit));
}

/// Sets @c destination to 0, clears the overflow, carry and negative flags, sets the zero flag.
template <typename IntT> void clear(IntT &destination, Status &status) {
	destination = 0;
	status.negative_flag = status.overflow_flag = status.carry_flag = status.zero_result = 0;
}

template <Operation operation, typename FlowController>
void apply_sr_ccr(uint16_t source, Status &status, FlowController &flow_controller) {
	static_assert(
		operation == Operation::ANDItoSR ||	operation == Operation::ANDItoCCR ||
		operation == Operation::EORItoSR ||	operation == Operation::EORItoCCR ||
		operation == Operation::ORItoSR ||	operation == Operation::ORItoCCR
	);

	auto sr = status.status();
	switch(operation) {
		case Operation::ANDItoSR:	case Operation::ANDItoCCR:
			sr &= source;
		break;
		case Operation::EORItoSR:	case Operation::EORItoCCR:
			sr ^= source;
		break;
		case Operation::ORItoSR:	case Operation::ORItoCCR:
			sr |= source;
		break;
	}

	switch(operation) {
		case Operation::ANDItoSR:
		case Operation::EORItoSR:
		case Operation::ORItoSR:
			status.set_status(sr);
			flow_controller.did_update_status();
		break;

		case Operation::ANDItoCCR:
		case Operation::EORItoCCR:
		case Operation::ORItoCCR:
			status.set_ccr(sr);
		break;
	}
}

template <bool is_mulu, typename FlowController>
void multiply(uint16_t source, uint32_t &destination, Status &status, FlowController &flow_controller) {
	if constexpr (is_mulu) {
		destination = source * uint16_t(destination);
	} else {
		destination = u_extend16(source) * u_extend16(uint16_t(destination));
	}
	status.carry_flag = status.overflow_flag = 0;
	status.zero_result = destination;
	status.negative_flag = status.zero_result & top_bit<uint32_t>();

	if constexpr (is_mulu) {
		flow_controller.did_mulu(source);
	} else {
		flow_controller.did_muls(source);
	}
}

template <bool is_divu, bool did_overflow, typename IntT, typename FlowController>
void did_divide(IntT dividend, IntT divisor, FlowController &flow_controller) {
	if constexpr (is_divu) {
		flow_controller.template did_divu<did_overflow>(dividend, divisor);
	} else {
		flow_controller.template did_divs<did_overflow>(dividend, divisor);
	}
}

template <bool is_divu, typename Int16, typename Int32, typename FlowController>
void divide(uint16_t source, uint32_t &destination, Status &status, FlowController &flow_controller) {
	status.carry_flag = 0;

	const auto dividend = Int32(destination);
	const auto divisor = Int32(Int16(source));

	if(!divisor) {
		status.negative_flag = status.overflow_flag = 0;
		status.zero_result = 1;
		flow_controller.raise_exception(Exception::IntegerDivideByZero);
		did_divide<is_divu, false>(dividend, divisor, flow_controller);
		return;
	}

	const auto quotient = int64_t(dividend) / int64_t(divisor);
	if(quotient != Int32(Int16(quotient))) {
		status.overflow_flag = 1;
		did_divide<is_divu, true>(dividend, divisor, flow_controller);
		return;
	}

	const auto remainder = Int16(dividend % divisor);
	destination = uint32_t((uint32_t(remainder) << 16) | uint16_t(quotient));

	status.overflow_flag = 0;
	status.zero_result = Status::FlagT(quotient);
	status.negative_flag = status.zero_result & 0x8000;
	did_divide<is_divu, false>(dividend, divisor, flow_controller);
}

template <typename IntT> void move(IntT source, IntT &destination, Status &status) {
	destination = source;
	status.zero_result = Status::FlagT(source);
	status.negative_flag = status.zero_result & top_bit<IntT>();
	status.overflow_flag = status.carry_flag = 0;
}

template <bool is_extend, typename IntT> void negative(IntT &source, Status &status) {
	const IntT result = -source - (is_extend && status.extend_flag ? 1 : 0);

	if constexpr (is_extend) {
		status.zero_result |= result;
	} else {
		status.zero_result = result;
	}
	status.extend_flag = status.carry_flag = result;	// i.e. any value other than 0 will result in carry.
	status.negative_flag = result & top_bit<IntT>();
	status.overflow_flag = Primitive::overflow<false>(source, IntT(0), result);

	source = result;
}

}

template <
	Model model,
	typename FlowController,
	Operation operation = Operation::Undefined
> void perform(Preinstruction instruction, CPU::SlicedInt32 &src, CPU::SlicedInt32 &dest, Status &status, FlowController &flow_controller) {

	switch((operation != Operation::Undefined) ? operation : instruction.operation) {
		/*
			ABCD adds the lowest bytes from the source and destination using BCD arithmetic,
			obeying the extend flag.
		*/
		case Operation::ABCD: {
			// Pull out the two halves, for simplicity.
			const uint8_t source = src.b;
			const uint8_t destination = dest.b;
			const int extend = (status.extend_flag ? 1 : 0);

			// Perform the BCD add by evaluating the two nibbles separately.
			const int unadjusted_result = destination + source + extend;
			int result = (destination & 0xf) + (source & 0xf) + extend;
			result +=
				(destination & 0xf0) +
				(source & 0xf0) +
				(((9 - result) >> 4) & 0x06);			// i.e. ((result > 0x09) ? 0x06 : 0x00)
			result += ((0x9f - result) >> 4) & 0x60;	// i.e. ((result > 0x9f) ? 0x60 : 0x00)

			// Set all flags essentially as if this were normal addition.
			status.zero_result |= result & 0xff;
			status.extend_flag = status.carry_flag = uint_fast32_t(result & ~0xff);
			status.negative_flag = result & 0x80;
			status.overflow_flag = ~unadjusted_result & result & 0x80;

			// Store the result.
			dest.b = uint8_t(result);
		} break;

		// ADD and ADDA add two quantities, the latter sign extending and without setting any flags;
		// ADDQ and SUBQ act as ADD and SUB, but taking the second argument from the instruction code.
		case Operation::ADDb:	Primitive::add_sub<true, false>(src.b, dest.b, status);		break;
		case Operation::SUBb:	Primitive::add_sub<false, false>(src.b, dest.b, status);	break;
		case Operation::ADDXb:	Primitive::add_sub<true, true>(src.b, dest.b, status);		break;
		case Operation::SUBXb:	Primitive::add_sub<false, true>(src.b, dest.b, status);		break;

		case Operation::ADDw:	Primitive::add_sub<true, false>(src.w, dest.w, status);		break;
		case Operation::SUBw:	Primitive::add_sub<false, false>(src.w, dest.w, status);	break;
		case Operation::ADDXw:	Primitive::add_sub<true, true>(src.w, dest.w, status);		break;
		case Operation::SUBXw:	Primitive::add_sub<false, true>(src.w, dest.w, status);		break;

		case Operation::ADDl:	Primitive::add_sub<true, false>(src.l, dest.l, status);		break;
		case Operation::SUBl:	Primitive::add_sub<false, false>(src.l, dest.l, status);	break;
		case Operation::ADDXl:	Primitive::add_sub<true, true>(src.l, dest.l, status);		break;
		case Operation::SUBXl:	Primitive::add_sub<false, true>(src.l, dest.l, status);		break;

		case Operation::ADDAw:	dest.l += u_extend16(src.w);	break;
		case Operation::ADDAl:	dest.l += src.l;				break;
		case Operation::SUBAw:	dest.l -= u_extend16(src.w);	break;
		case Operation::SUBAl:	dest.l -= src.l;				break;

		// BTST/BCLR/etc: modulo for the mask depends on whether memory or a data register is the target.
		case Operation::BTST:
			status.zero_result = dest.l & (1 << Primitive::mask_bit(instruction, src.l));
		break;
		case Operation::BCLR:	Primitive::bit_manipulate<Operation::BCLR>(instruction, src.l, dest.l, status, flow_controller);	break;
		case Operation::BCHG:	Primitive::bit_manipulate<Operation::BCHG>(instruction, src.l, dest.l, status, flow_controller);	break;
		case Operation::BSET:	Primitive::bit_manipulate<Operation::BSET>(instruction, src.l, dest.l, status, flow_controller);	break;

		case Operation::Bccb:
			flow_controller.template complete_bcc<int8_t>(
				status.evaluate_condition(instruction.condition()),
				int8_t(src.b));
		break;

		case Operation::Bccw:
			flow_controller.template complete_bcc<int16_t>(
				status.evaluate_condition(instruction.condition()),
				int16_t(src.w));
		break;

		case Operation::Bccl:
			flow_controller.template complete_bcc<int32_t>(
				status.evaluate_condition(instruction.condition()),
				int32_t(src.l));
		break;

		case Operation::BSRb:
			flow_controller.bsr(uint32_t(int8_t(src.b)));
		break;
		case Operation::BSRw:
			flow_controller.bsr(uint32_t(int16_t(src.w)));
		break;
		case Operation::BSRl:
			flow_controller.bsr(src.l);
		break;

		case Operation::DBcc: {
			const bool matched_condition = status.evaluate_condition(instruction.condition());
			bool overflowed = false;

			// Classify the dbcc.
			if(!matched_condition) {
				-- src.w;
				overflowed = src.w == 0xffff;
			}

			// Take the branch.
			flow_controller.complete_dbcc(
				matched_condition,
				overflowed,
				int16_t(dest.w));
		} break;

		case Operation::Scc: {
			const bool condition = status.evaluate_condition(instruction.condition());
			src.b = condition ? 0xff : 0x00;
			flow_controller.did_scc(condition);
		} break;

		/*
			CLRs: store 0 to the destination, set the zero flag, and clear
			negative, overflow and carry.
		*/
		case Operation::CLRb:	Primitive::clear(src.b, status);	break;
		case Operation::CLRw:	Primitive::clear(src.w, status);	break;
		case Operation::CLRl:	Primitive::clear(src.l, status);	break;

		/*
			CMP.b, CMP.l and CMP.w: sets the condition flags (other than extend) based on a subtraction
			of the source from the destination; the result of the subtraction is not stored.
		*/
		case Operation::CMPb:	Primitive::compare(src.b, dest.b, status);	break;
		case Operation::CMPw:	Primitive::compare(src.w, dest.w, status);	break;
		case Operation::CMPAw:	Primitive::compare(u_extend16(src.w), dest.l, status);	break;
		case Operation::CMPAl:
		case Operation::CMPl:	Primitive::compare(src.l, dest.l, status);	break;

		// JMP: copies EA(0) to the program counter.
		case Operation::JMP:
			flow_controller.jmp(src.l);
		break;

		// JSR: jump to EA(0), pushing the current PC to the stack.
		case Operation::JSR:
			flow_controller.jsr(src.l);
		break;

		/*
			MOVE.b, MOVE.l and MOVE.w: move the least significant byte or word, or the entire long word,
			and set negative, zero, overflow and carry as appropriate.
		*/
		case Operation::MOVEb:	Primitive::move(src.b, dest.b, status);	break;
		case Operation::MOVEw:	Primitive::move(src.w, dest.w, status);	break;
		case Operation::MOVEl:	Primitive::move(src.l, dest.l, status);	break;

		/*
			MOVEA.l: move the entire long word;
			MOVEA.w: move the least significant word and sign extend it.
			Neither sets any flags.
		*/
		case Operation::MOVEAw:
			dest.l = u_extend16(src.w);
		break;

		case Operation::MOVEAl:
			dest.l = src.l;
		break;

		case Operation::LEA:
			dest.l = src.l;
		break;

		case Operation::PEA:
			flow_controller.pea(src.l);
		break;

		/*
			Status word moves and manipulations.
		*/

		case Operation::MOVEtoSR:
			status.set_status(src.w);
			flow_controller.did_update_status();
		break;

		case Operation::MOVEfromSR:
			src.w = status.status();
		break;

		case Operation::MOVEtoCCR:
			status.set_ccr(src.w);
		break;

		case Operation::MOVEtoUSP:
			flow_controller.move_to_usp(src.l);
		break;

		case Operation::MOVEfromUSP:
			flow_controller.move_from_usp(src.l);
		break;

		case Operation::EXTbtow:
			src.w = uint16_t(int8_t(src.b));
			status.overflow_flag = status.carry_flag = 0;
			status.zero_result = src.w;
			status.negative_flag = status.zero_result & 0x8000;
		break;

		case Operation::EXTwtol:
			src.l = u_extend16(src.w);
			status.overflow_flag = status.carry_flag = 0;
			status.zero_result = src.l;
			status.negative_flag = status.zero_result & 0x80000000;
		break;

		case Operation::ANDItoSR:	Primitive::apply_sr_ccr<Operation::ANDItoSR>(src.w, status, flow_controller);	break;
		case Operation::EORItoSR:	Primitive::apply_sr_ccr<Operation::EORItoSR>(src.w, status, flow_controller);	break;
		case Operation::ORItoSR:	Primitive::apply_sr_ccr<Operation::ORItoSR>(src.w, status, flow_controller);	break;
		case Operation::ANDItoCCR:	Primitive::apply_sr_ccr<Operation::ANDItoCCR>(src.w, status, flow_controller);	break;
		case Operation::EORItoCCR:	Primitive::apply_sr_ccr<Operation::EORItoCCR>(src.w, status, flow_controller);	break;
		case Operation::ORItoCCR:	Primitive::apply_sr_ccr<Operation::ORItoCCR>(src.w, status, flow_controller);	break;

		/*
			Multiplications.
		*/

		case Operation::MULU:	Primitive::multiply<true>(src.w, dest.l, status, flow_controller);	break;
		case Operation::MULS:	Primitive::multiply<false>(src.w, dest.l, status, flow_controller);	break;

		/*
			Divisions.
		*/

		case Operation::DIVU:	Primitive::divide<true, uint16_t, uint32_t>(src.w, dest.l, status, flow_controller);	break;
		case Operation::DIVS:	Primitive::divide<false, int16_t, int32_t>(src.w, dest.l, status, flow_controller);		break;

		// TRAP, which is a nicer form of ILLEGAL.
		case Operation::TRAP:
			flow_controller.template raise_exception<false>(int(src.l + Exception::TrapBase));
		break;

		case Operation::TRAPV: {
			if(status.overflow_flag) {
				flow_controller.template raise_exception<false>(Exception::TRAPV);
			}
		} break;

		case Operation::CHK: {
			const bool is_under = s_extend16(dest.w) < 0;
			const bool is_over = s_extend16(dest.w) > s_extend16(src.w);

			status.overflow_flag = status.carry_flag = 0;
			status.zero_result = dest.w;

			// Test applied for N:
			//
			//	if Dn < 0, set negative flag;
			//	otherwise, if Dn > <ea>, reset negative flag.
			if(is_over)		status.negative_flag = 0;
			if(is_under)	status.negative_flag = 1;

			// No exception is the default course of action; deviate only if an
			// exception is necessary.
			flow_controller.did_chk(is_under, is_over);
			if(is_under || is_over) {
				flow_controller.template raise_exception<false>(Exception::CHK);
			}
		} break;

		/*
			NEGs: negatives the destination, setting the zero,
			negative, overflow and carry flags appropriate, and extend.

			NB: since the same logic as SUB is used to calculate overflow,
			and SUB calculates `destination - source`, the NEGs deliberately
			label 'source' and 'destination' differently from Motorola.
		*/
		case Operation::NEGb:	Primitive::negative<false>(src.b, status);		break;
		case Operation::NEGw:	Primitive::negative<false>(src.w, status);		break;
		case Operation::NEGl:	Primitive::negative<false>(src.l, status);		break;

		/*
			NEGXs: NEG, with extend.
		*/
		case Operation::NEGXb:	Primitive::negative<true>(src.b, status);		break;
		case Operation::NEGXw:	Primitive::negative<true>(src.w, status);		break;
		case Operation::NEGXl:	Primitive::negative<true>(src.l, status);		break;

		/*
			The no-op.
		*/
		case Operation::NOP:	break;

		/*
			LINK and UNLINK help with stack frames, allowing a certain
			amount of stack space to be allocated or deallocated.
		*/

		case Operation::LINKw:
			flow_controller.link(instruction, uint32_t(int16_t(dest.w)));
		break;

		case Operation::UNLINK:
			flow_controller.unlink(src.l);
		break;

		/*
			TAS: sets zero and negative depending on the current value of the destination,
			and sets the high bit, using a specialised atomic bus cycle.
		*/

		case Operation::TAS:
			flow_controller.tas(instruction, src.l);
		break;

		/*
			Bitwise operators: AND, OR and EOR. All three clear the overflow and carry flags,
			and set zero and negative appropriately.
		*/
#define op_and(x, y)	x &= y
#define op_or(x, y)		x |= y
#define op_eor(x, y)	x ^= y

#define bitwise(source, dest, sign_mask, operator)	\
	operator(dest, source);							\
	status.overflow_flag = status.carry_flag = 0;	\
	status.zero_result = dest;						\
	status.negative_flag = dest & sign_mask;

#define andx(source, dest, sign_mask)	bitwise(source, dest, sign_mask, op_and)
#define eorx(source, dest, sign_mask)	bitwise(source, dest, sign_mask, op_eor)
#define orx(source, dest, sign_mask)	bitwise(source, dest, sign_mask, op_or)

#define op_bwl(name, op)											\
	case Operation::name##b: op(src.b, dest.b, 0x80);		break;	\
	case Operation::name##w: op(src.w, dest.w, 0x8000);		break;	\
	case Operation::name##l: op(src.l, dest.l, 0x80000000);	break;

		op_bwl(AND, andx);
		op_bwl(EOR, eorx);
		op_bwl(OR, orx);

#undef op_bwl
#undef orx
#undef eorx
#undef andx
#undef bitwise
#undef op_eor
#undef op_or
#undef op_and

		// NOTs: take the logical inverse, affecting the negative and zero flags.
		case Operation::NOTb:
			src.b ^= 0xff;
			status.zero_result = src.b;
			status.negative_flag = status.zero_result & 0x80;
			status.overflow_flag = status.carry_flag = 0;
		break;

		case Operation::NOTw:
			src.w ^= 0xffff;
			status.zero_result = src.w;
			status.negative_flag = status.zero_result & 0x8000;
			status.overflow_flag = status.carry_flag = 0;
		break;

		case Operation::NOTl:
			src.l ^= 0xffffffff;
			status.zero_result = src.l;
			status.negative_flag = status.zero_result & 0x80000000;
			status.overflow_flag = status.carry_flag = 0;
		break;

#define sbcd(d)																					\
	const int extend = (status.extend_flag ? 1 : 0);											\
	const int unadjusted_result = destination - source - extend;								\
																								\
	const int top = (destination & 0xf0) - (source & 0xf0) - (0x60 & (unadjusted_result >> 4));	\
																								\
	int result = (destination & 0xf) - (source & 0xf) - extend;									\
	const int low_adjustment = 0x06 & (result >> 4);											\
	status.extend_flag = status.carry_flag = Status::FlagT(										\
		(unadjusted_result - low_adjustment) & 0x300											\
	);																							\
	result = result + top - low_adjustment;														\
																								\
	/* Store the result. */																		\
	d = uint8_t(result);																		\
																								\
	/* Set all remaining flags essentially as if this were normal subtraction. */				\
	status.zero_result |= d;														\
	status.negative_flag = result & 0x80;														\
	status.overflow_flag = unadjusted_result & ~result & 0x80;									\

		/*
			SBCD subtracts the lowest byte of the source from that of the destination using
			BCD arithmetic, obeying the extend flag.
		*/
		case Operation::SBCD: {
			const uint8_t source = src.b;
			const uint8_t destination = dest.b;
			sbcd(dest.b);
		} break;

		/*
			NBCD is like SBCD except that the result is 0 - source rather than
			destination - source.
		*/
		case Operation::NBCD: {
			const uint8_t source = src.b;
			const uint8_t destination = 0;
			sbcd(src.b);
		} break;

#undef sbcd

		// EXG and SWAP exchange/swap words or long words.

		case Operation::EXG: {
			const auto temporary = src.l;
			src.l = dest.l;
			dest.l = temporary;
		} break;

		case Operation::SWAP: {
			uint16_t *const words = reinterpret_cast<uint16_t *>(&src.l);
			const auto temporary = words[0];
			words[0] = words[1];
			words[1] = temporary;

			status.zero_result = src.l;
			status.negative_flag = temporary & 0x8000;
			status.overflow_flag = status.carry_flag = 0;
		} break;

		/*
			Shifts and rotates.
		*/
#define set_neg_zero(v, m)														\
	status.zero_result = Status::FlagT(v);						\
	status.negative_flag = status.zero_result & Status::FlagT(m);

#define set_neg_zero_overflow(v, m)									\
	set_neg_zero(v, m);												\
	status.overflow_flag = (Status::FlagT(value) ^ status.zero_result) & Status::FlagT(m);

#define decode_shift_count(type)	\
	int shift_count = src.l & 63;	\
	flow_controller.template did_shift<type>(shift_count);

#define set_flags_w(t) set_flags(src.w, 0x8000, t)

#define asl(destination, size)	{\
	decode_shift_count(decltype(destination)); \
	const auto value = destination;	\
	\
	if(!shift_count) {	\
		status.carry_flag = status.overflow_flag = 0;	\
	} else {	\
		destination = (shift_count < size) ? decltype(destination)(value << shift_count) : 0;	\
		status.extend_flag = status.carry_flag = Status::FlagT(value) & Status::FlagT( (1u << (size - 1)) >> (shift_count - 1) );	\
		\
		if(shift_count >= size) status.overflow_flag = value && (value != decltype(value)(-1));	\
		else {	\
			const auto mask = decltype(destination)(0xffffffff << (size - shift_count));	\
			status.overflow_flag = mask & value && ((mask & value) != mask);	\
		}	\
	}	\
	\
	set_neg_zero(destination, 1 << (size - 1));	\
}

		case Operation::ASLm: {
			const auto value = src.w;
			src.w = uint16_t(value << 1);
			status.extend_flag = status.carry_flag = value & 0x8000;
			set_neg_zero_overflow(src.w, 0x8000);
		} break;
		case Operation::ASLb: asl(dest.b, 8);	break;
		case Operation::ASLw: asl(dest.w, 16); 	break;
		case Operation::ASLl: asl(dest.l, 32); 	break;

#define asr(destination, size)	{\
	decode_shift_count(decltype(destination));	\
	const auto value = destination;	\
	\
	if(!shift_count) {	\
		status.carry_flag = 0;	\
	} else {	\
		destination = (shift_count < size) ?	\
		decltype(destination)(\
			(value >> shift_count) |	\
			((value & decltype(value)(1 << (size - 1)) ? 0xffffffff : 0x000000000) << (size - shift_count))	\
		) :	\
			decltype(destination)(	\
			(value & decltype(value)(1 << (size - 1))) ? 0xffffffff : 0x000000000	\
		);	\
		status.extend_flag = status.carry_flag = Status::FlagT(value) & Status::FlagT(1 << (shift_count - 1));	\
	}	\
	\
	set_neg_zero_overflow(destination, 1 << (size - 1));	\
}

		case Operation::ASRm: {
			const auto value = src.w;
			src.w = (value&0x8000) | (value >> 1);
			status.extend_flag = status.carry_flag = value & 1;
			set_neg_zero_overflow(src.w, 0x8000);
		} break;
		case Operation::ASRb: asr(dest.b, 8);	break;
		case Operation::ASRw: asr(dest.w, 16); 	break;
		case Operation::ASRl: asr(dest.l, 32); 	break;


#undef set_neg_zero_overflow
#define set_neg_zero_overflow(v, m)	\
	set_neg_zero(v, m);	\
	status.overflow_flag = 0;

#undef set_flags
#define set_flags(v, m, t)	\
	status.zero_result = v;	\
	status.negative_flag = status.zero_result & (m);	\
	status.overflow_flag = 0;	\
	status.carry_flag = value & (t);

#define lsl(destination, size)	{\
	decode_shift_count(decltype(destination));	\
	const auto value = destination;	\
	\
	if(!shift_count) {	\
		status.carry_flag = 0;	\
	} else {	\
		destination = (shift_count < size) ? decltype(destination)(value << shift_count) : 0;	\
		status.extend_flag = status.carry_flag = Status::FlagT(value) & Status::FlagT( (1u << (size - 1)) >> (shift_count - 1) );	\
	}	\
	\
	set_neg_zero_overflow(destination, 1 << (size - 1));	\
}

		case Operation::LSLm: {
			const auto value = src.w;
			src.w = uint16_t(value << 1);
			status.extend_flag = status.carry_flag = value & 0x8000;
			set_neg_zero_overflow(src.w, 0x8000);
		} break;
		case Operation::LSLb: lsl(dest.b, 8);	break;
		case Operation::LSLw: lsl(dest.w, 16); 	break;
		case Operation::LSLl: lsl(dest.l, 32); 	break;

#define lsr(destination, size)	{\
	decode_shift_count(decltype(destination));	\
	const auto value = destination;	\
	\
	if(!shift_count) {	\
		status.carry_flag = 0;	\
	} else {	\
		destination = (shift_count < size) ? (value >> shift_count) : 0;	\
		status.extend_flag = status.carry_flag = value & Status::FlagT(1 << (shift_count - 1));	\
	}	\
	\
	set_neg_zero_overflow(destination, 1 << (size - 1));	\
}

		case Operation::LSRm: {
			const auto value = src.w;
			src.w = value >> 1;
			status.extend_flag = status.carry_flag = value & 1;
			set_neg_zero_overflow(src.w, 0x8000);
		} break;
		case Operation::LSRb: lsr(dest.b, 8);	break;
		case Operation::LSRw: lsr(dest.w, 16); 	break;
		case Operation::LSRl: lsr(dest.l, 32); 	break;

#define rol(destination, size)	{ \
	decode_shift_count(decltype(destination));	\
	const auto value = destination;	\
	\
	if(!shift_count) {	\
		status.carry_flag = 0;	\
	} else {	\
		shift_count &= (size - 1);	\
		destination = decltype(destination)(	\
			(value << shift_count) |	\
			(value >> (size - shift_count))	\
		);	\
		status.carry_flag = Status::FlagT(destination & 1);	\
	}	\
	\
	set_neg_zero_overflow(destination, 1 << (size - 1));	\
}

		case Operation::ROLm: {
			const auto value = src.w;
			src.w = uint16_t((value << 1) | (value >> 15));
			status.carry_flag = src.w & 1;
			set_neg_zero_overflow(src.w, 0x8000);
		} break;
		case Operation::ROLb: rol(dest.b, 8);	break;
		case Operation::ROLw: rol(dest.w, 16); 	break;
		case Operation::ROLl: rol(dest.l, 32); 	break;

#define ror(destination, size)	{ \
	decode_shift_count(decltype(destination));	\
	const auto value = destination;	\
	\
	if(!shift_count) {	\
		status.carry_flag = 0;	\
	} else {	\
		shift_count &= (size - 1);	\
		destination = decltype(destination)(\
			(value >> shift_count) |	\
			(value << (size - shift_count))	\
		);\
		status.carry_flag = destination & Status::FlagT(1 << (size - 1));	\
	}	\
	\
	set_neg_zero_overflow(destination, 1 << (size - 1));	\
}

		case Operation::RORm: {
			const auto value = src.w;
			src.w = uint16_t((value >> 1) | (value << 15));
			status.carry_flag = src.w & 0x8000;
			set_neg_zero_overflow(src.w, 0x8000);
		} break;
		case Operation::RORb: ror(dest.b, 8);	break;
		case Operation::RORw: ror(dest.w, 16); 	break;
		case Operation::RORl: ror(dest.l, 32); 	break;

#define roxl(destination, size)	{ \
	decode_shift_count(decltype(destination));	\
	\
	shift_count %= (size + 1);	\
	uint64_t compound = uint64_t(destination) | (status.extend_flag ? (1ull << size) : 0);	\
	compound = \
		(compound << shift_count) |	\
		(compound >> (size + 1 - shift_count));	\
	status.carry_flag = status.extend_flag = Status::FlagT((compound >> size) & 1);	\
	destination = decltype(destination)(compound);	\
	\
	set_neg_zero_overflow(destination, 1 << (size - 1));	\
}

		case Operation::ROXLm: {
			const auto value = src.w;
			src.w = uint16_t((value << 1) | (status.extend_flag ? 0x0001 : 0x0000));
			status.extend_flag = value & 0x8000;
			set_flags_w(0x8000);
		} break;
		case Operation::ROXLb: roxl(dest.b, 8);		break;
		case Operation::ROXLw: roxl(dest.w, 16); 	break;
		case Operation::ROXLl: roxl(dest.l, 32); 	break;

#define roxr(destination, size)	{ \
	decode_shift_count(decltype(destination));	\
	\
	shift_count %= (size + 1);	\
	uint64_t compound = uint64_t(destination) | (status.extend_flag ? (1ull << size) : 0);	\
	compound = \
		(compound >> shift_count) |	\
		(compound << (size + 1 - shift_count));	\
		status.carry_flag = status.extend_flag = Status::FlagT((compound >> size) & 1);	\
	destination = decltype(destination)(compound);	\
	\
	set_neg_zero_overflow(destination, 1 << (size - 1));	\
}

		case Operation::ROXRm: {
			const auto value = src.w;
			src.w = (value >> 1) | (status.extend_flag ? 0x8000 : 0x0000);
			status.extend_flag = value & 0x0001;
			set_flags_w(0x0001);
		} break;
		case Operation::ROXRb: roxr(dest.b, 8);		break;
		case Operation::ROXRw: roxr(dest.w, 16); 	break;
		case Operation::ROXRl: roxr(dest.l, 32); 	break;

#undef roxr
#undef roxl
#undef ror
#undef rol
#undef asr
#undef lsr
#undef lsl
#undef asl

#undef set_flags
#undef decode_shift_count
#undef set_flags_w
#undef set_neg_zero_overflow
#undef set_neg_zero

		case Operation::MOVEPl:
			flow_controller.template movep<uint32_t>(instruction, src.l, dest.l);
		break;

		case Operation::MOVEPw:
			flow_controller.template movep<uint16_t>(instruction, src.l, dest.l);
		break;

		case Operation::MOVEMtoRl:
			flow_controller.template movem_toR<uint32_t>(instruction, src.l, dest.l);
		break;

		case Operation::MOVEMtoMl:
			flow_controller.template movem_toM<uint32_t>(instruction, src.l, dest.l);
		break;

		case Operation::MOVEMtoRw:
			flow_controller.template movem_toR<uint16_t>(instruction, src.l, dest.l);
		break;

		case Operation::MOVEMtoMw:
			flow_controller.template movem_toM<uint16_t>(instruction, src.l, dest.l);
		break;

		/*
			RTE and RTR share an implementation.
		*/
		case Operation::RTR:
			flow_controller.rtr();
		break;

		case Operation::RTE:
			flow_controller.rte();
		break;

		case Operation::RTS:
			flow_controller.rts();
		break;

		/*
			TSTs: compare to zero.
		*/

		case Operation::TSTb:
			status.carry_flag = status.overflow_flag = 0;
			status.zero_result = src.b;
			status.negative_flag = status.zero_result & 0x80;
		break;

		case Operation::TSTw:
			status.carry_flag = status.overflow_flag = 0;
			status.zero_result = src.w;
			status.negative_flag = status.zero_result & 0x8000;
		break;

		case Operation::TSTl:
			status.carry_flag = status.overflow_flag = 0;
			status.zero_result = src.l;
			status.negative_flag = status.zero_result & 0x80000000;
		break;

		case Operation::STOP:
			status.set_status(src.w);
			flow_controller.did_update_status();
			flow_controller.stop();
		break;

		case Operation::RESET:
			flow_controller.reset();
		break;

		/*
			Development period debugging.
		*/
		default:
			assert(false);
		break;
	}

#undef u_extend16
#undef s_extend16

}

}
}

#endif /* InstructionSets_M68k_PerformImplementation_h */