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110 lines
2.8 KiB
C++
110 lines
2.8 KiB
C++
/**
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* \file libimp/uninitialized.h
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* \author mutouyun (orz@orzz.org)
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* \brief Uninitialized memory algorithms.
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* \date 2022-02-27
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*/
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#pragma once
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#include <new> // placement-new
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#include <type_traits> // std::enable_if_t
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#include <utility> // std::forward
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#include <memory> // std::construct_at, std::destroy_at, std::addressof
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#include <cstddef>
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#include "libimp/def.h"
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#include "libimp/detect_plat.h"
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#include "libimp/horrible_cast.h"
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LIBIMP_NAMESPACE_BEG_
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/**
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* \brief Creates an object at a given address, like 'construct_at' in c++20
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* \see https://en.cppreference.com/w/cpp/memory/construct_at
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*/
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template <typename T, typename... A>
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auto construct(void *p, A &&...args)
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-> std::enable_if_t<::std::is_constructible<T, A...>::value, T *> {
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#if defined(LIBIMP_CPP_20)
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return std::construct_at(static_cast<T *>(p), std::forward<A>(args)...);
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#else
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return ::new (p) T(std::forward<A>(args)...);
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#endif
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}
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template <typename T, typename... A>
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auto construct(void *p, A &&...args)
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-> std::enable_if_t<!::std::is_constructible<T, A...>::value, T *> {
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return ::new (p) T{std::forward<A>(args)...};
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}
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/**
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* \brief Destroys an object at a given address, like 'destroy_at' in c++17
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* \see https://en.cppreference.com/w/cpp/memory/destroy_at
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*/
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template <typename T>
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void *destroy(T *p) noexcept {
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if (p == nullptr) return nullptr;
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#if defined(LIBIMP_CPP_17)
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std::destroy_at(p);
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#else
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p->~T();
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#endif
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return p;
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}
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template <typename T, std::size_t N>
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void *destroy(T (*p)[N]) noexcept {
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if (p == nullptr) return nullptr;
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#if defined(LIBIMP_CPP_20)
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std::destroy_at(p);
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#elif defined(LIBIMP_CPP_17)
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std::destroy(std::begin(*p), std::end(*p));
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#else
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for (auto &elem : *p) destroy(std::addressof(elem));
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#endif
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return p;
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}
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/**
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* \brief Destroys a range of objects.
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* \see https://en.cppreference.com/w/cpp/memory/destroy
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*/
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template <typename ForwardIt>
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void destroy(ForwardIt first, ForwardIt last) noexcept {
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#if defined(LIBIMP_CPP_17)
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std::destroy(first, last);
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#else
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for (; first != last; ++first) {
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destroy(std::addressof(*first));
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}
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#endif
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}
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/**
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* \brief Constructs objects by default-initialization
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* in an uninitialized area of memory, defined by a start and a count.
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* \see https://en.cppreference.com/w/cpp/memory/uninitialized_default_construct_n
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*/
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template <typename ForwardIt, typename Size>
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ForwardIt uninitialized_default_construct_n(ForwardIt first, Size n) {
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#if defined(LIBIMP_CPP_17)
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return std::uninitialized_default_construct_n(first, n);
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#else
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using T = typename std::iterator_traits<ForwardIt>::value_type;
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ForwardIt current = first;
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LIBIMP_TRY {
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for (; n > 0; (void) ++current, --n)
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::new (horrible_cast<void *>(std::addressof(*current))) T;
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return current;
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} LIBIMP_CATCH(...) {
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destroy(first, current);
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LIBIMP_THROW(, first);
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}
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#endif
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}
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LIBIMP_NAMESPACE_END_
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