/*
 *  yosys -- Yosys Open SYnthesis Suite
 *
 *  Copyright (C) 2019-2020  whitequark <whitequark@whitequark.org>
 *
 *  Permission to use, copy, modify, and/or distribute this software for any
 *  purpose with or without fee is hereby granted.
 *
 *  THE SOFTWARE IS PROVIDED "AS IS" AND THE AUTHOR DISCLAIMS ALL WARRANTIES
 *  WITH REGARD TO THIS SOFTWARE INCLUDING ALL IMPLIED WARRANTIES OF
 *  MERCHANTABILITY AND FITNESS. IN NO EVENT SHALL THE AUTHOR BE LIABLE FOR
 *  ANY SPECIAL, DIRECT, INDIRECT, OR CONSEQUENTIAL DAMAGES OR ANY DAMAGES
 *  WHATSOEVER RESULTING FROM LOSS OF USE, DATA OR PROFITS, WHETHER IN AN
 *  ACTION OF CONTRACT, NEGLIGENCE OR OTHER TORTIOUS ACTION, ARISING OUT OF
 *  OR IN CONNECTION WITH THE USE OR PERFORMANCE OF THIS SOFTWARE.
 *
 */

// This file is included by the designs generated with `write_cxxrtl`. It is not used in Yosys itself.

#ifndef CXXRTL_H
#define CXXRTL_H

#include <cstddef>
#include <cstdint>
#include <cassert>
#include <limits>
#include <type_traits>
#include <tuple>
#include <vector>
#include <map>
#include <algorithm>
#include <memory>
#include <sstream>

// The cxxrtl support library implements compile time specialized arbitrary width arithmetics, as well as provides
// composite lvalues made out of bit slices and concatenations of lvalues. This allows the `write_cxxrtl` pass
// to perform a straightforward translation of RTLIL structures to readable C++, relying on the C++ compiler
// to unwrap the abstraction and generate efficient code.
namespace cxxrtl {

// All arbitrary-width values in cxxrtl are backed by arrays of unsigned integers called chunks. The chunk size
// is the same regardless of the value width to simplify manipulating values via FFI interfaces, e.g. driving
// and introspecting the simulation in Python.
//
// It is practical to use chunk sizes between 32 bits and platform register size because when arithmetics on
// narrower integer types is legalized by the C++ compiler, it inserts code to clear the high bits of the register.
// However, (a) most of our operations do not change those bits in the first place because of invariants that are
// invisible to the compiler, (b) we often operate on non-power-of-2 values and have to clear the high bits anyway.
// Therefore, using relatively wide chunks and clearing the high bits explicitly and only when we know they may be
// clobbered results in simpler generated code.
template<typename T>
struct chunk_traits {
	static_assert(std::is_integral<T>::value && std::is_unsigned<T>::value,
	              "chunk type must be an unsigned integral type");
	using type = T;
	static constexpr size_t bits = std::numeric_limits<T>::digits;
	static constexpr T mask = std::numeric_limits<T>::max();
};

template<class T>
struct expr_base;

template<size_t Bits>
struct value : public expr_base<value<Bits>> {
	static constexpr size_t bits = Bits;

	using chunk = chunk_traits<uint32_t>;
	static constexpr chunk::type msb_mask = (Bits % chunk::bits == 0) ? chunk::mask
		: chunk::mask >> (chunk::bits - (Bits % chunk::bits));

	static constexpr size_t chunks = (Bits + chunk::bits - 1) / chunk::bits;
	chunk::type data[chunks] = {};

	value() = default;
	template<typename... Init>
	explicit constexpr value(Init ...init) : data{init...} {}

	value(const value<Bits> &) = default;
	value(value<Bits> &&) = default;
	value<Bits> &operator=(const value<Bits> &) = default;

	// A (no-op) helper that forces the cast to value<>.
	const value<Bits> &val() const {
		return *this;
	}

	std::string str() const {
		std::stringstream ss;
		ss << *this;
		return ss.str();
	}

	// Operations with compile-time parameters.
	//
	// These operations are used to implement slicing, concatenation, and blitting.
	// The trunc, zext and sext operations add or remove most significant bits (i.e. on the left);
	// the rtrunc and rzext operations add or remove least significant bits (i.e. on the right).
	template<size_t NewBits>
	value<NewBits> trunc() const {
		static_assert(NewBits <= Bits, "trunc() may not increase width");
		value<NewBits> result;
		for (size_t n = 0; n < result.chunks; n++)
			result.data[n] = data[n];
		result.data[result.chunks - 1] &= result.msb_mask;
		return result;
	}

	template<size_t NewBits>
	value<NewBits> zext() const {
		static_assert(NewBits >= Bits, "zext() may not decrease width");
		value<NewBits> result;
		for (size_t n = 0; n < chunks; n++)
			result.data[n] = data[n];
		return result;
	}

	template<size_t NewBits>
	value<NewBits> sext() const {
		static_assert(NewBits >= Bits, "sext() may not decrease width");
		value<NewBits> result;
		for (size_t n = 0; n < chunks; n++)
			result.data[n] = data[n];
		if (is_neg()) {
			result.data[chunks - 1] |= ~msb_mask;
			for (size_t n = chunks; n < result.chunks; n++)
				result.data[n] = chunk::mask;
			result.data[result.chunks - 1] &= result.msb_mask;
		}
		return result;
	}

	template<size_t NewBits>
	value<NewBits> rtrunc() const {
		static_assert(NewBits <= Bits, "rtrunc() may not increase width");
		value<NewBits> result;
		constexpr size_t shift_chunks = (Bits - NewBits) / chunk::bits;
		constexpr size_t shift_bits   = (Bits - NewBits) % chunk::bits;
		chunk::type carry = 0;
		if (shift_chunks + result.chunks < chunks) {
			carry = (shift_bits == 0) ? 0
				: data[shift_chunks + result.chunks] << (chunk::bits - shift_bits);
		}
		for (size_t n = result.chunks; n > 0; n--) {
			result.data[n - 1] = carry | (data[shift_chunks + n - 1] >> shift_bits);
			carry = (shift_bits == 0) ? 0
				: data[shift_chunks + n - 1] << (chunk::bits - shift_bits);
		}
		return result;
	}

	template<size_t NewBits>
	value<NewBits> rzext() const {
		static_assert(NewBits >= Bits, "rzext() may not decrease width");
		value<NewBits> result;
		constexpr size_t shift_chunks = (NewBits - Bits) / chunk::bits;
		constexpr size_t shift_bits   = (NewBits - Bits) % chunk::bits;
		chunk::type carry = 0;
		for (size_t n = 0; n < chunks; n++) {
			result.data[shift_chunks + n] = (data[n] << shift_bits) | carry;
			carry = (shift_bits == 0) ? 0
				: data[n] >> (chunk::bits - shift_bits);
		}
		if (carry != 0)
			result.data[result.chunks - 1] = carry;
		return result;
	}

	// Bit blit operation, i.e. a partial read-modify-write.
	template<size_t Stop, size_t Start>
	value<Bits> blit(const value<Stop - Start + 1> &source) const {
		static_assert(Stop >= Start, "blit() may not reverse bit order");
		constexpr chunk::type start_mask = ~(chunk::mask << (Start % chunk::bits));
		constexpr chunk::type stop_mask = (Stop % chunk::bits + 1 == chunk::bits) ? 0
			: (chunk::mask << (Stop % chunk::bits + 1));
		value<Bits> masked = *this;
		if (Start / chunk::bits == Stop / chunk::bits) {
			masked.data[Start / chunk::bits] &= stop_mask | start_mask;
		} else {
			masked.data[Start / chunk::bits] &= start_mask;
			for (size_t n = Start / chunk::bits + 1; n < Stop / chunk::bits; n++)
				masked.data[n] = 0;
			masked.data[Stop / chunk::bits] &= stop_mask;
		}
		value<Bits> shifted = source
			.template rzext<Stop + 1>()
			.template zext<Bits>();
		return masked.bit_or(shifted);
	}

	// Helpers for selecting extending or truncating operation depending on whether the result is wider or narrower
	// than the operand. In C++17 these can be replaced with `if constexpr`.
	template<size_t NewBits, typename = void>
	struct zext_cast {
		value<NewBits> operator()(const value<Bits> &val) {
			return val.template zext<NewBits>();
		}
	};

	template<size_t NewBits>
	struct zext_cast<NewBits, typename std::enable_if<(NewBits < Bits)>::type> {
		value<NewBits> operator()(const value<Bits> &val) {
			return val.template trunc<NewBits>();
		}
	};

	template<size_t NewBits, typename = void>
	struct sext_cast {
		value<NewBits> operator()(const value<Bits> &val) {
			return val.template sext<NewBits>();
		}
	};

	template<size_t NewBits>
	struct sext_cast<NewBits, typename std::enable_if<(NewBits < Bits)>::type> {
		value<NewBits> operator()(const value<Bits> &val) {
			return val.template trunc<NewBits>();
		}
	};

	template<size_t NewBits>
	value<NewBits> zcast() const {
		return zext_cast<NewBits>()(*this);
	}

	template<size_t NewBits>
	value<NewBits> scast() const {
		return sext_cast<NewBits>()(*this);
	}

	// Operations with run-time parameters (offsets, amounts, etc).
	//
	// These operations are used for computations.
	bool bit(size_t offset) const {
		return data[offset / chunk::bits] & (1 << (offset % chunk::bits));
	}

	void set_bit(size_t offset, bool value = true) {
		size_t offset_chunks = offset / chunk::bits;
		size_t offset_bits = offset % chunk::bits;
		data[offset_chunks] &= ~(1 << offset_bits);
		data[offset_chunks] |= value ? 1 << offset_bits : 0;
	}

	bool is_zero() const {
		for (size_t n = 0; n < chunks; n++)
			if (data[n] != 0)
				return false;
		return true;
	}

	explicit operator bool() const {
		return !is_zero();
	}

	bool is_neg() const {
		return data[chunks - 1] & (1 << ((Bits - 1) % chunk::bits));
	}

	bool operator ==(const value<Bits> &other) const {
		for (size_t n = 0; n < chunks; n++)
			if (data[n] != other.data[n])
				return false;
		return true;
	}

	bool operator !=(const value<Bits> &other) const {
		return !(*this == other);
	}

	value<Bits> bit_not() const {
		value<Bits> result;
		for (size_t n = 0; n < chunks; n++)
			result.data[n] = ~data[n];
		result.data[chunks - 1] &= msb_mask;
		return result;
	}

	value<Bits> bit_and(const value<Bits> &other) const {
		value<Bits> result;
		for (size_t n = 0; n < chunks; n++)
			result.data[n] = data[n] & other.data[n];
		return result;
	}

	value<Bits> bit_or(const value<Bits> &other) const {
		value<Bits> result;
		for (size_t n = 0; n < chunks; n++)
			result.data[n] = data[n] | other.data[n];
		return result;
	}

	value<Bits> bit_xor(const value<Bits> &other) const {
		value<Bits> result;
		for (size_t n = 0; n < chunks; n++)
			result.data[n] = data[n] ^ other.data[n];
		return result;
	}

	value<Bits> update(const value<Bits> &val, const value<Bits> &mask) const {
		return bit_and(mask.bit_not()).bit_or(val.bit_and(mask));
	}

	template<size_t AmountBits>
	value<Bits> shl(const value<AmountBits> &amount) const {
		// Ensure our early return is correct by prohibiting values larger than 4 Gbit.
		static_assert(Bits <= chunk::mask, "shl() of unreasonably large values is not supported");
		// Detect shifts definitely large than Bits early.
		for (size_t n = 1; n < amount.chunks; n++)
			if (amount.data[n] != 0)
				return {};
		// Past this point we can use the least significant chunk as the shift size.
		size_t shift_chunks = amount.data[0] / chunk::bits;
		size_t shift_bits   = amount.data[0] % chunk::bits;
		if (shift_chunks >= chunks)
			return {};
		value<Bits> result;
		chunk::type carry = 0;
		for (size_t n = 0; n < chunks - shift_chunks; n++) {
			result.data[shift_chunks + n] = (data[n] << shift_bits) | carry;
			carry = (shift_bits == 0) ? 0
				: data[n] >> (chunk::bits - shift_bits);
		}
		return result;
	}

	template<size_t AmountBits, bool Signed = false>
	value<Bits> shr(const value<AmountBits> &amount) const {
		// Ensure our early return is correct by prohibiting values larger than 4 Gbit.
		static_assert(Bits <= chunk::mask, "shr() of unreasonably large values is not supported");
		// Detect shifts definitely large than Bits early.
		for (size_t n = 1; n < amount.chunks; n++)
			if (amount.data[n] != 0)
				return {};
		// Past this point we can use the least significant chunk as the shift size.
		size_t shift_chunks = amount.data[0] / chunk::bits;
		size_t shift_bits   = amount.data[0] % chunk::bits;
		if (shift_chunks >= chunks)
			return {};
		value<Bits> result;
		chunk::type carry = 0;
		for (size_t n = 0; n < chunks - shift_chunks; n++) {
			result.data[chunks - shift_chunks - 1 - n] = carry | (data[chunks - 1 - n] >> shift_bits);
			carry = (shift_bits == 0) ? 0
				: data[chunks - 1 - n] << (chunk::bits - shift_bits);
		}
		if (Signed && is_neg()) {
			for (size_t n = chunks - shift_chunks; n < chunks; n++)
				result.data[n] = chunk::mask;
			if (shift_bits != 0)
				result.data[chunks - shift_chunks] |= chunk::mask << (chunk::bits - shift_bits);
		}
		return result;
	}

	template<size_t AmountBits>
	value<Bits> sshr(const value<AmountBits> &amount) const {
		return shr<AmountBits, /*Signed=*/true>(amount);
	}

	size_t ctpop() const {
		size_t count = 0;
		for (size_t n = 0; n < chunks; n++) {
			// This loop implements the population count idiom as recognized by LLVM and GCC.
			for (chunk::type x = data[n]; x != 0; count++)
				x = x & (x - 1);
		}
		return count;
	}

	size_t ctlz() const {
		size_t count = 0;
		for (size_t n = 0; n < chunks; n++) {
			chunk::type x = data[chunks - 1 - n];
			if (x == 0) {
				count += (n == 0 ? Bits % chunk::bits : chunk::bits);
			} else {
				// This loop implements the find first set idiom as recognized by LLVM.
				for (; x != 0; count++)
					x >>= 1;
			}
		}
		return count;
	}

	template<bool Invert, bool CarryIn>
	std::pair<value<Bits>, bool /*CarryOut*/> alu(const value<Bits> &other) const {
		value<Bits> result;
		bool carry = CarryIn;
		for (size_t n = 0; n < result.chunks; n++) {
			result.data[n] = data[n] + (Invert ? ~other.data[n] : other.data[n]) + carry;
			carry = (result.data[n] <  data[n]) ||
			        (result.data[n] == data[n] && carry);
		}
		result.data[result.chunks - 1] &= result.msb_mask;
		return {result, carry};
	}

	value<Bits> add(const value<Bits> &other) const {
		return alu</*Invert=*/false, /*CarryIn=*/false>(other).first;
	}

	value<Bits> sub(const value<Bits> &other) const {
		return alu</*Invert=*/true, /*CarryIn=*/true>(other).first;
	}

	value<Bits> neg() const {
		return value<Bits> { 0u }.sub(*this);
	}

	bool ucmp(const value<Bits> &other) const {
		bool carry;
		std::tie(std::ignore, carry) = alu</*Invert=*/true, /*CarryIn=*/true>(other);
		return !carry; // a.ucmp(b) ≡ a u< b
	}

	bool scmp(const value<Bits> &other) const {
		value<Bits> result;
		bool carry;
		std::tie(result, carry) = alu</*Invert=*/true, /*CarryIn=*/true>(other);
		bool overflow = (is_neg() == !other.is_neg()) && (is_neg() != result.is_neg());
		return result.is_neg() ^ overflow; // a.scmp(b) ≡ a s< b
	}
};

// Expression template for a slice, usable as lvalue or rvalue, and composable with other expression templates here.
template<class T, size_t Stop, size_t Start>
struct slice_expr : public expr_base<slice_expr<T, Stop, Start>> {
	static_assert(Stop >= Start, "slice_expr() may not reverse bit order");
	static_assert(Start < T::bits && Stop < T::bits, "slice_expr() must be within bounds");
	static constexpr size_t bits = Stop - Start + 1;

	T &expr;

	slice_expr(T &expr) : expr(expr) {}
	slice_expr(const slice_expr<T, Stop, Start> &) = delete;

	operator value<bits>() const {
		return static_cast<const value<T::bits> &>(expr)
			.template rtrunc<T::bits - Start>()
			.template trunc<bits>();
	}

	slice_expr<T, Stop, Start> &operator=(const value<bits> &rhs) {
		// Generic partial assignment implemented using a read-modify-write operation on the sliced expression.
		expr = static_cast<const value<T::bits> &>(expr)
			.template blit<Stop, Start>(rhs);
		return *this;
	}

	// A helper that forces the cast to value<>, which allows deduction to work.
	value<bits> val() const {
		return static_cast<const value<bits> &>(*this);
	}
};

// Expression template for a concatenation, usable as lvalue or rvalue, and composable with other expression templates here.
template<class T, class U>
struct concat_expr : public expr_base<concat_expr<T, U>> {
	static constexpr size_t bits = T::bits + U::bits;

	T &ms_expr;
	U &ls_expr;

	concat_expr(T &ms_expr, U &ls_expr) : ms_expr(ms_expr), ls_expr(ls_expr) {}
	concat_expr(const concat_expr<T, U> &) = delete;

	operator value<bits>() const {
		value<bits> ms_shifted = static_cast<const value<T::bits> &>(ms_expr)
			.template rzext<bits>();
		value<bits> ls_extended = static_cast<const value<U::bits> &>(ls_expr)
			.template zext<bits>();
		return ms_shifted.bit_or(ls_extended);
	}

	concat_expr<T, U> &operator=(const value<bits> &rhs) {
		ms_expr = rhs.template rtrunc<T::bits>();
		ls_expr = rhs.template trunc<U::bits>();
		return *this;
	}

	// A helper that forces the cast to value<>, which allows deduction to work.
	value<bits> val() const {
		return static_cast<const value<bits> &>(*this);
	}
};

// Base class for expression templates, providing helper methods for operations that are valid on both rvalues and lvalues.
//
// Note that expression objects (slices and concatenations) constructed in this way should NEVER be captured because
// they refer to temporaries that will, in general, only live until the end of the statement. For example, both of
// these snippets perform use-after-free:
//
//    const auto &a = val.slice<7,0>().slice<1>();
//    value<1> b = a;
//
//    auto &&c = val.slice<7,0>().slice<1>();
//    c = value<1>{1u};
//
// An easy way to write code using slices and concatenations safely is to follow two simple rules:
//   * Never explicitly name any type except `value<W>` or `const value<W> &`.
//   * Never use a `const auto &` or `auto &&` in any such expression.
// Then, any code that compiles will be well-defined.
template<class T>
struct expr_base {
	template<size_t Stop, size_t Start = Stop>
	slice_expr<const T, Stop, Start> slice() const {
		return {*static_cast<const T *>(this)};
	}

	template<size_t Stop, size_t Start = Stop>
	slice_expr<T, Stop, Start> slice() {
		return {*static_cast<T *>(this)};
	}

	template<class U>
	concat_expr<const T, typename std::remove_reference<const U>::type> concat(const U &other) const {
		return {*static_cast<const T *>(this), other};
	}

	template<class U>
	concat_expr<T, typename std::remove_reference<U>::type> concat(U &&other) {
		return {*static_cast<T *>(this), other};
	}
};

template<size_t Bits>
std::ostream &operator<<(std::ostream &os, const value<Bits> &val) {
	auto old_flags = os.flags(std::ios::right);
	auto old_width = os.width(0);
	auto old_fill  = os.fill('0');
	os << val.bits << '\'' << std::hex;
	for (size_t n = val.chunks - 1; n != (size_t)-1; n--) {
		if (n == val.chunks - 1 && Bits % value<Bits>::chunk::bits != 0)
			os.width((Bits % value<Bits>::chunk::bits + 3) / 4);
		else
			os.width((value<Bits>::chunk::bits + 3) / 4);
		os << val.data[n];
	}
	os.fill(old_fill);
	os.width(old_width);
	os.flags(old_flags);
	return os;
}

template<size_t Bits>
struct wire {
	static constexpr size_t bits = Bits;

	value<Bits> curr;
	value<Bits> next;

	wire() = default;
	constexpr wire(const value<Bits> &init) : curr(init), next(init) {}
	template<typename... Init>
	explicit constexpr wire(Init ...init) : curr{init...}, next{init...} {}

	wire(const wire<Bits> &) = delete;
	wire(wire<Bits> &&) = default;
	wire<Bits> &operator=(const wire<Bits> &) = delete;

	bool commit() {
		if (curr != next) {
			curr = next;
			return true;
		}
		return false;
	}
};

template<size_t Bits>
std::ostream &operator<<(std::ostream &os, const wire<Bits> &val) {
	os << val.curr;
	return os;
}

template<size_t Width>
struct memory {
	std::vector<value<Width>> data;

	size_t depth() const {
		return data.size();
	}

	memory() = delete;
	explicit memory(size_t depth) : data(depth) {}

	memory(const memory<Width> &) = delete;
	memory<Width> &operator=(const memory<Width> &) = delete;

	// The only way to get the compiler to put the initializer in .rodata and do not copy it on stack is to stuff it
	// into a plain array. You'd think an std::initializer_list would work here, but it doesn't, because you can't
	// construct an initializer_list in a constexpr (or something) and so if you try to do that the whole thing is
	// first copied on the stack (probably overflowing it) and then again into `data`.
	template<size_t Size>
	struct init {
		size_t offset;
		value<Width> data[Size];
	};

	template<size_t... InitSize>
	explicit memory(size_t depth, const init<InitSize> &...init) : data(depth) {
		data.resize(depth);
		// This utterly reprehensible construct is the most reasonable way to apply a function to every element
		// of a parameter pack, if the elements all have different types and so cannot be cast to an initializer list.
		auto _ = {std::move(std::begin(init.data), std::end(init.data), data.begin() + init.offset)...};
	}

	// An operator for direct memory reads. May be used at any time during the simulation.
	const value<Width> &operator [](size_t index) const {
		assert(index < data.size());
		return data[index];
	}

	// An operator for direct memory writes. May only be used before the simulation is started. If used
	// after the simulation is started, the design may malfunction.
	value<Width> &operator [](size_t index) {
		assert(index < data.size());
		return data[index];
	}

	// A simple way to make a writable memory would be to use an array of wires instead of an array of values.
	// However, there are two significant downsides to this approach: first, it has large overhead (2× space
	// overhead, and O(depth) time overhead during commit); second, it does not simplify handling write port
	// priorities. Although in principle write ports could be ordered or conditionally enabled in generated
	// code based on their priorities and selected addresses, the feedback arc set problem is computationally
	// expensive, and the heuristic based algorithms are not easily modified to guarantee (rather than prefer)
	// a particular write port evaluation order.
	//
	// The approach used here instead is to queue writes into a buffer during the eval phase, then perform
	// the writes during the commit phase in the priority order. This approach has low overhead, with both space
	// and time proportional to the amount of write ports. Because virtually every memory in a practical design
	// has at most two write ports, linear search is used on every write, being the fastest and simplest approach.
	struct write {
		size_t index;
		value<Width> val;
		value<Width> mask;
		int priority;
	};
	std::vector<write> write_queue;

	void update(size_t index, const value<Width> &val, const value<Width> &mask, int priority = 0) {
		assert(index < data.size());
		// Queue up the write while keeping the queue sorted by priority.
		write_queue.insert(
			std::upper_bound(write_queue.begin(), write_queue.end(), priority,
				[](const int a, const write& b) { return a < b.priority; }),
			write { index, val, mask, priority });
	}

	bool commit() {
		bool changed = false;
		for (const write &entry : write_queue) {
			value<Width> elem = data[entry.index];
			elem = elem.update(entry.val, entry.mask);
			changed |= (data[entry.index] != elem);
			data[entry.index] = elem;
		}
		write_queue.clear();
		return changed;
	}
};

struct metadata {
	const enum {
		MISSING = 0,
		UINT   	= 1,
		SINT   	= 2,
		STRING 	= 3,
		DOUBLE 	= 4,
	} value_type;

	// In debug mode, using the wrong .as_*() function will assert.
	// In release mode, using the wrong .as_*() function will safely return a default value.
	union {
		const unsigned  uint_value = 0;
		const signed    sint_value;
	};
	const std::string string_value = "";
	const double      double_value = 0.0;

	metadata() : value_type(MISSING) {}
	metadata(unsigned value) : value_type(UINT), uint_value(value) {}
	metadata(signed value) : value_type(SINT), sint_value(value) {}
	metadata(const std::string &value) : value_type(STRING), string_value(value) {}
	metadata(const char *value) : value_type(STRING), string_value(value) {}
	metadata(double value) : value_type(DOUBLE), double_value(value) {}

	metadata(const metadata &) = default;
	metadata &operator=(const metadata &) = delete;

	unsigned as_uint() const {
		assert(value_type == UINT);
		return uint_value;
	}

	signed as_sint() const {
		assert(value_type == SINT);
		return sint_value;
	}

	const std::string &as_string() const {
		assert(value_type == STRING);
		return string_value;
	}

	double as_double() const {
		assert(value_type == DOUBLE);
		return double_value;
	}
};

typedef std::map<std::string, metadata> metadata_map;

struct module {
	module() {}
	virtual ~module() {}

	module(const module &) = delete;
	module &operator=(const module &) = delete;

	virtual bool eval() = 0;
	virtual bool commit() = 0;

	size_t step() {
		size_t deltas = 0;
		bool converged = false;
		do {
			converged = eval();
			deltas++;
		} while (commit() && !converged);
		return deltas;
	}
};

} // namespace cxxrtl

// Definitions of internal Yosys cells. Other than the functions in this namespace, cxxrtl is fully generic
// and indepenent of Yosys implementation details.
//
// The `write_cxxrtl` pass translates internal cells (cells with names that start with `$`) to calls of these
// functions. All of Yosys arithmetic and logical cells perform sign or zero extension on their operands,
// whereas basic operations on arbitrary width values require operands to be of the same width. These functions
// bridge the gap by performing the necessary casts. They are named similar to `cell_A[B]`, where A and B are `u`
// if the corresponding operand is unsigned, and `s` if it is signed.
namespace cxxrtl_yosys {

using namespace cxxrtl;

// std::max isn't constexpr until C++14 for no particular reason (it's an oversight), so we define our own.
template<class T>
constexpr T max(const T &a, const T &b) {
	return a > b ? a : b;
}

// Logic operations
template<size_t BitsY, size_t BitsA>
value<BitsY> not_u(const value<BitsA> &a) {
	return a.template zcast<BitsY>().bit_not();
}

template<size_t BitsY, size_t BitsA>
value<BitsY> not_s(const value<BitsA> &a) {
	return a.template scast<BitsY>().bit_not();
}

template<size_t BitsY, size_t BitsA>
value<BitsY> logic_not_u(const value<BitsA> &a) {
	return value<BitsY> { a ? 0u : 1u };
}

template<size_t BitsY, size_t BitsA>
value<BitsY> logic_not_s(const value<BitsA> &a) {
	return value<BitsY> { a ? 0u : 1u };
}

template<size_t BitsY, size_t BitsA>
value<BitsY> reduce_and_u(const value<BitsA> &a) {
	return value<BitsY> { a.bit_not().is_zero() ? 1u : 0u };
}

template<size_t BitsY, size_t BitsA>
value<BitsY> reduce_and_s(const value<BitsA> &a) {
	return value<BitsY> { a.bit_not().is_zero() ? 1u : 0u };
}

template<size_t BitsY, size_t BitsA>
value<BitsY> reduce_or_u(const value<BitsA> &a) {
	return value<BitsY> { a ? 1u : 0u };
}

template<size_t BitsY, size_t BitsA>
value<BitsY> reduce_or_s(const value<BitsA> &a) {
	return value<BitsY> { a ? 1u : 0u };
}

template<size_t BitsY, size_t BitsA>
value<BitsY> reduce_xor_u(const value<BitsA> &a) {
	return value<BitsY> { (a.ctpop() % 2) ? 1u : 0u };
}

template<size_t BitsY, size_t BitsA>
value<BitsY> reduce_xor_s(const value<BitsA> &a) {
	return value<BitsY> { (a.ctpop() % 2) ? 1u : 0u };
}

template<size_t BitsY, size_t BitsA>
value<BitsY> reduce_xnor_u(const value<BitsA> &a) {
	return value<BitsY> { (a.ctpop() % 2) ? 0u : 1u };
}

template<size_t BitsY, size_t BitsA>
value<BitsY> reduce_xnor_s(const value<BitsA> &a) {
	return value<BitsY> { (a.ctpop() % 2) ? 0u : 1u };
}

template<size_t BitsY, size_t BitsA>
value<BitsY> reduce_bool_u(const value<BitsA> &a) {
	return value<BitsY> { a ? 1u : 0u };
}

template<size_t BitsY, size_t BitsA>
value<BitsY> reduce_bool_s(const value<BitsA> &a) {
	return value<BitsY> { a ? 1u : 0u };
}

template<size_t BitsY, size_t BitsA, size_t BitsB>
value<BitsY> and_uu(const value<BitsA> &a, const value<BitsB> &b) {
	return a.template zcast<BitsY>().bit_and(b.template zcast<BitsY>());
}

template<size_t BitsY, size_t BitsA, size_t BitsB>
value<BitsY> and_ss(const value<BitsA> &a, const value<BitsB> &b) {
	return a.template scast<BitsY>().bit_and(b.template scast<BitsY>());
}

template<size_t BitsY, size_t BitsA, size_t BitsB>
value<BitsY> or_uu(const value<BitsA> &a, const value<BitsB> &b) {
	return a.template zcast<BitsY>().bit_or(b.template zcast<BitsY>());
}

template<size_t BitsY, size_t BitsA, size_t BitsB>
value<BitsY> or_ss(const value<BitsA> &a, const value<BitsB> &b) {
	return a.template scast<BitsY>().bit_or(b.template scast<BitsY>());
}

template<size_t BitsY, size_t BitsA, size_t BitsB>
value<BitsY> xor_uu(const value<BitsA> &a, const value<BitsB> &b) {
	return a.template zcast<BitsY>().bit_xor(b.template zcast<BitsY>());
}

template<size_t BitsY, size_t BitsA, size_t BitsB>
value<BitsY> xor_ss(const value<BitsA> &a, const value<BitsB> &b) {
	return a.template scast<BitsY>().bit_xor(b.template scast<BitsY>());
}

template<size_t BitsY, size_t BitsA, size_t BitsB>
value<BitsY> xnor_uu(const value<BitsA> &a, const value<BitsB> &b) {
	return a.template zcast<BitsY>().bit_xor(b.template zcast<BitsY>()).bit_not();
}

template<size_t BitsY, size_t BitsA, size_t BitsB>
value<BitsY> xnor_ss(const value<BitsA> &a, const value<BitsB> &b) {
	return a.template scast<BitsY>().bit_xor(b.template scast<BitsY>()).bit_not();
}

template<size_t BitsY, size_t BitsA, size_t BitsB>
value<BitsY> logic_and_uu(const value<BitsA> &a, const value<BitsB> &b) {
	return value<BitsY> { (bool(a) & bool(b)) ? 1u : 0u };
}

template<size_t BitsY, size_t BitsA, size_t BitsB>
value<BitsY> logic_and_ss(const value<BitsA> &a, const value<BitsB> &b) {
	return value<BitsY> { (bool(a) & bool(b)) ? 1u : 0u };
}

template<size_t BitsY, size_t BitsA, size_t BitsB>
value<BitsY> logic_or_uu(const value<BitsA> &a, const value<BitsB> &b) {
	return value<BitsY> { (bool(a) | bool(b)) ? 1u : 0u };
}

template<size_t BitsY, size_t BitsA, size_t BitsB>
value<BitsY> logic_or_ss(const value<BitsA> &a, const value<BitsB> &b) {
	return value<BitsY> { (bool(a) | bool(b)) ? 1u : 0u };
}

template<size_t BitsY, size_t BitsA, size_t BitsB>
value<BitsY> shl_uu(const value<BitsA> &a, const value<BitsB> &b) {
	return a.template zcast<BitsY>().template shl(b);
}

template<size_t BitsY, size_t BitsA, size_t BitsB>
value<BitsY> shl_su(const value<BitsA> &a, const value<BitsB> &b) {
	return a.template scast<BitsY>().template shl(b);
}

template<size_t BitsY, size_t BitsA, size_t BitsB>
value<BitsY> sshl_uu(const value<BitsA> &a, const value<BitsB> &b) {
	return a.template zcast<BitsY>().template shl(b);
Basics

Mutual exclusion by System Locks

Advantages

Disadvantages

When use Locks

Example

Mutual exclusion by Semaphores

Advantages

Disadvantages

When use Semaphores

Example

Mutual exclusion by Mutexes

Advantages

Disadvantages

When use Mutexes

Example

Mutual exclusion by priority boost

Advantages

Disadvantages

Example

Mutual exclusion by message passing

Advantages

Disadvantages
