rexylib/include/rexy/allocator.hpp

/**
	This file is a part of rexy's general purpose library
	Copyright (C) 2020-2022 rexy712

	This program is free software: you can redistribute it and/or modify
	it under the terms of the GNU General Public License as published by
	the Free Software Foundation, either version 3 of the License, or
	(at your option) any later version.

	This program is distributed in the hope that it will be useful,
	but WITHOUT ANY WARRANTY; without even the implied warranty of
	MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
	GNU General Public License for more details.

	You should have received a copy of the GNU General Public License
	along with this program.  If not, see <http://www.gnu.org/licenses/>.
*/

#ifndef REXY_DEFAULT_ALLOCATOR_HPP
#define REXY_DEFAULT_ALLOCATOR_HPP

#include <cstddef> //ptrdiff_t, size_t
#include <type_traits> //true_type, false_type, is_constant_evaluated
#include <new>
#include <limits> //numeric_limits

#if __cplusplus >= 202002L
	#include <memory> //allocator
#endif

#ifdef __cpp_concepts
	#include "concepts/allocator.hpp"
	#define REXY_ALLOCATOR_CONCEPT Allocator
#else
	#define REXY_ALLOCATOR_CONCEPT class
#endif

#include "rexy.hpp"
#include "compat/standard.hpp"

#include <type_traits> //declval

namespace rexy{

	template<class T>
	struct allocator
	{
		using pointer = T*;
		using const_pointer = const T*;
		using void_pointer = void*;
		using const_void_pointer = const void*;
		using value_type = T;
		using size_type = size_t;
		using difference_type = ptrdiff_t;
		using is_always_equal = std::true_type;
		using propagate_on_container_copy_assignment = std::false_type;
		using propagate_on_container_move_assignment = std::false_type;
		using propagate_on_container_swap = std::false_type;

		template<class U>
		struct rebind{
			using other = allocator<U>;
		};

	private:
		constexpr bool has_overflow(size_type n)const{
			return n > max_size();
		}

	public:
		REXY_CPP20_CONSTEXPR allocator(void) = default;
		REXY_CPP20_CONSTEXPR allocator(const allocator&) = default;
		REXY_CPP20_CONSTEXPR allocator(allocator&&) = default;
		template<class U>
		constexpr allocator(const allocator<U>&)noexcept{}
		REXY_CPP20_CONSTEXPR ~allocator(void) = default;

		//'::operator new' is never a constexpr call as of C++23. However, 'std::allocator::allocate' *is* transiently constexpr as of C++20,
		//even though it directly calls '::operator new' as is stated in the standard. Therefore, when evaluating this call with support for
		//'if consteval', we can use the 'std::allocator::allocate' constexpr-ness when this is in a constant evaluation context.
#if __cplusplus >= 202002L
		REXY_CPP20_CONSTEXPR pointer allocate(size_type n){
			size_type bytes = has_overflow(n) ? std::numeric_limits<size_type>::max() : n*sizeof(T);

			#ifdef __cpp_if_consteval
				if consteval{  //} //makes my braces matcher in nano not upset ;)
			#else
				if(std::is_constant_evaluated()){
			#endif //__cpp_if_consteval
					std::allocator<value_type> a;
					const size_type num_items = n / sizeof(value_type);
					return a.allocate(num_items);
				}else{
					if constexpr(alignof(T) <= __STDCPP_DEFAULT_NEW_ALIGNMENT__){
						return reinterpret_cast<pointer>(::operator new(bytes));
					}else{
						return reinterpret_cast<pointer>(::operator new(bytes, static_cast<std::align_val_t>(alignof(T))));
					}
				} //if consteval
		}


		REXY_CPP20_CONSTEXPR void deallocate(pointer p, size_type n){
			#ifdef __cpp_if_consteval
				if consteval{  //} //makes my braces matcher in nano not upset ;)
			#else
				if(std::is_constant_evaluated()){
			#endif
					std::allocator<value_type> a;
					const size_type num_items = n / sizeof(value_type);
					return a.deallocate(p, num_items);
				}else{

				#if !defined(__cpp_sized_deallocation)
					//clang does not enable ::operator delete(void* ptr, std::size_t sz) by default for some reason
					if constexpr(alignof(T) <= __STDCPP_DEFAULT_NEW_ALIGNMENT__){
						::operator delete(p);
					}else{
						::operator delete(p, static_cast<std::align_val_t>(alignof(T)));
					}
				#else //__cpp_sized_deallocation
					size_type bytes = has_overflow(n) ? std::numeric_limits<size_type>::max() : n*sizeof(T);
					if constexpr(alignof(T) <= __STDCPP_DEFAULT_NEW_ALIGNMENT__){
						::operator delete(p, bytes);
					}else{
						::operator delete(p, bytes, static_cast<std::align_val_t>(alignof(T)));
					}
				#endif //__cpp_sized_deallocation

			} //if consteval

		}
#else //__cplusplus
		REXY_CPP20_CONSTEXPR pointer allocate(size_type n){
			size_type bytes = has_overflow(n) ? std::numeric_limits<size_type>::max() : n*sizeof(T);

			if constexpr(alignof(T) <= __STDCPP_DEFAULT_NEW_ALIGNMENT__){
				return reinterpret_cast<pointer>(::operator new(bytes));
			}else{
				return reinterpret_cast<pointer>(::operator new(bytes, static_cast<std::align_val_t>(alignof(T))));
			}
		}
		REXY_CPP20_CONSTEXPR void deallocate(pointer p, size_type n){
			#if !defined(__cpp_sized_deallocation)
				//clang does not enable ::operator delete(void* ptr, std::size_t sz) by default for some reason
				if constexpr(alignof(T) <= __STDCPP_DEFAULT_NEW_ALIGNMENT__){
					::operator delete(p);
				}else{
					::operator delete(p, static_cast<std::align_val_t>(alignof(T)));
				}
			#else //__cpp_sized_deallocation
			size_type bytes = has_overflow(n) ? std::numeric_limits<size_type>::max() : n*sizeof(T);
				if constexpr(alignof(T) <= __STDCPP_DEFAULT_NEW_ALIGNMENT__){
					::operator delete(p, bytes);
				}else{
					::operator delete(p, bytes, static_cast<std::align_val_t>(alignof(T)));
				}
			#endif //__cpp_sized_deallocation

		}
#endif //__cplusplus
		constexpr size_type max_size(void)const{
			return std::numeric_limits<size_type>::max()/sizeof(T);
		}
	};
	template<class T, class U>
	constexpr bool operator==(const allocator<T>&, const allocator<U>&){
		return true;
	}
	template<class T, class U>
	constexpr bool operator!=(const allocator<T>&, const allocator<U>&){
		return false;
	}

	template<REXY_ALLOCATOR_CONCEPT T>
	struct is_nothrow_allocator{
		static constexpr bool value = noexcept(std::declval<T>().allocate(0)) && noexcept(std::declval<T>().deallocate(nullptr, 0));
	};
	template<REXY_ALLOCATOR_CONCEPT T>
	static constexpr bool is_nothrow_allocator_v = is_nothrow_allocator<T>::value;

}

#endif