569 lines
14 KiB
C++
569 lines
14 KiB
C++
// The -*- C++ -*- type traits classes for internal use in libstdc++
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// Copyright (C) 2000-2022 Free Software Foundation, Inc.
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//
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// This file is part of the GNU ISO C++ Library. This library is free
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// software; you can redistribute it and/or modify it under the
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// terms of the GNU General Public License as published by the
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// Free Software Foundation; either version 3, or (at your option)
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// any later version.
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// This library is distributed in the hope that it will be useful,
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// but WITHOUT ANY WARRANTY; without even the implied warranty of
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// MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
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// GNU General Public License for more details.
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// Under Section 7 of GPL version 3, you are granted additional
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// permissions described in the GCC Runtime Library Exception, version
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// 3.1, as published by the Free Software Foundation.
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// You should have received a copy of the GNU General Public License and
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// a copy of the GCC Runtime Library Exception along with this program;
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// see the files COPYING3 and COPYING.RUNTIME respectively. If not, see
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// <http://www.gnu.org/licenses/>.
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/** @file bits/cpp_type_traits.h
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* This is an internal header file, included by other library headers.
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* Do not attempt to use it directly. @headername{ext/type_traits}
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*/
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// Written by Gabriel Dos Reis <dosreis@cmla.ens-cachan.fr>
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#ifndef _CPP_TYPE_TRAITS_H
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#define _CPP_TYPE_TRAITS_H 1
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#pragma GCC system_header
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#include <bits/c++config.h>
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//
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// This file provides some compile-time information about various types.
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// These representations were designed, on purpose, to be constant-expressions
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// and not types as found in <bits/type_traits.h>. In particular, they
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// can be used in control structures and the optimizer hopefully will do
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// the obvious thing.
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//
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// Why integral expressions, and not functions nor types?
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// Firstly, these compile-time entities are used as template-arguments
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// so function return values won't work: We need compile-time entities.
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// We're left with types and constant integral expressions.
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// Secondly, from the point of view of ease of use, type-based compile-time
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// information is -not- *that* convenient. One has to write lots of
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// overloaded functions and to hope that the compiler will select the right
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// one. As a net effect, the overall structure isn't very clear at first
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// glance.
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// Thirdly, partial ordering and overload resolution (of function templates)
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// is highly costly in terms of compiler-resource. It is a Good Thing to
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// keep these resource consumption as least as possible.
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//
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// See valarray_array.h for a case use.
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//
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// -- Gaby (dosreis@cmla.ens-cachan.fr) 2000-03-06.
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//
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// Update 2005: types are also provided and <bits/type_traits.h> has been
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// removed.
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//
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extern "C++" {
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namespace std _GLIBCXX_VISIBILITY(default)
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{
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_GLIBCXX_BEGIN_NAMESPACE_VERSION
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struct __true_type { };
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struct __false_type { };
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template<bool>
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struct __truth_type
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{ typedef __false_type __type; };
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template<>
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struct __truth_type<true>
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{ typedef __true_type __type; };
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// N.B. The conversions to bool are needed due to the issue
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// explained in c++/19404.
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template<class _Sp, class _Tp>
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struct __traitor
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{
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enum { __value = bool(_Sp::__value) || bool(_Tp::__value) };
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typedef typename __truth_type<__value>::__type __type;
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};
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// Compare for equality of types.
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template<typename, typename>
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struct __are_same
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{
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enum { __value = 0 };
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typedef __false_type __type;
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};
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template<typename _Tp>
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struct __are_same<_Tp, _Tp>
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{
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enum { __value = 1 };
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typedef __true_type __type;
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};
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// Holds if the template-argument is a void type.
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template<typename _Tp>
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struct __is_void
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{
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enum { __value = 0 };
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typedef __false_type __type;
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};
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template<>
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struct __is_void<void>
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{
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enum { __value = 1 };
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typedef __true_type __type;
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};
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//
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// Integer types
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//
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template<typename _Tp>
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struct __is_integer
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{
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enum { __value = 0 };
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typedef __false_type __type;
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};
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// Thirteen specializations (yes there are eleven standard integer
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// types; <em>long long</em> and <em>unsigned long long</em> are
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// supported as extensions). Up to four target-specific __int<N>
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// types are supported as well.
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template<>
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struct __is_integer<bool>
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{
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enum { __value = 1 };
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typedef __true_type __type;
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};
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template<>
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struct __is_integer<char>
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{
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enum { __value = 1 };
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typedef __true_type __type;
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};
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template<>
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struct __is_integer<signed char>
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{
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enum { __value = 1 };
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typedef __true_type __type;
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};
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template<>
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struct __is_integer<unsigned char>
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{
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enum { __value = 1 };
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typedef __true_type __type;
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};
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# ifdef __WCHAR_TYPE__
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template<>
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struct __is_integer<wchar_t>
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{
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enum { __value = 1 };
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typedef __true_type __type;
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};
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# endif
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#ifdef _GLIBCXX_USE_CHAR8_T
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template<>
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struct __is_integer<char8_t>
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{
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enum { __value = 1 };
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typedef __true_type __type;
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};
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#endif
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#if __cplusplus >= 201103L
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template<>
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struct __is_integer<char16_t>
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{
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enum { __value = 1 };
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typedef __true_type __type;
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};
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template<>
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struct __is_integer<char32_t>
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{
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enum { __value = 1 };
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typedef __true_type __type;
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};
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#endif
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template<>
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struct __is_integer<short>
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{
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enum { __value = 1 };
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typedef __true_type __type;
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};
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template<>
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struct __is_integer<unsigned short>
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{
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enum { __value = 1 };
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typedef __true_type __type;
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};
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template<>
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struct __is_integer<int>
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{
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enum { __value = 1 };
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typedef __true_type __type;
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};
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template<>
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struct __is_integer<unsigned int>
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{
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enum { __value = 1 };
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typedef __true_type __type;
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};
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template<>
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struct __is_integer<long>
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{
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enum { __value = 1 };
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typedef __true_type __type;
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};
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template<>
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struct __is_integer<unsigned long>
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{
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enum { __value = 1 };
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typedef __true_type __type;
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};
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template<>
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struct __is_integer<long long>
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{
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enum { __value = 1 };
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typedef __true_type __type;
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};
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template<>
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struct __is_integer<unsigned long long>
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{
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enum { __value = 1 };
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typedef __true_type __type;
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};
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#define __INT_N(TYPE) \
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__extension__ \
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template<> \
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struct __is_integer<TYPE> \
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{ \
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enum { __value = 1 }; \
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typedef __true_type __type; \
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}; \
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__extension__ \
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template<> \
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struct __is_integer<unsigned TYPE> \
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{ \
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enum { __value = 1 }; \
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typedef __true_type __type; \
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};
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#ifdef __GLIBCXX_TYPE_INT_N_0
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__INT_N(__GLIBCXX_TYPE_INT_N_0)
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#endif
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#ifdef __GLIBCXX_TYPE_INT_N_1
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__INT_N(__GLIBCXX_TYPE_INT_N_1)
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#endif
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#ifdef __GLIBCXX_TYPE_INT_N_2
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__INT_N(__GLIBCXX_TYPE_INT_N_2)
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#endif
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#ifdef __GLIBCXX_TYPE_INT_N_3
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__INT_N(__GLIBCXX_TYPE_INT_N_3)
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#endif
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#undef __INT_N
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//
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// Floating point types
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//
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template<typename _Tp>
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struct __is_floating
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{
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enum { __value = 0 };
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typedef __false_type __type;
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};
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// three specializations (float, double and 'long double')
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template<>
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struct __is_floating<float>
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{
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enum { __value = 1 };
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typedef __true_type __type;
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};
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template<>
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struct __is_floating<double>
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{
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enum { __value = 1 };
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typedef __true_type __type;
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};
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template<>
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struct __is_floating<long double>
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{
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enum { __value = 1 };
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typedef __true_type __type;
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};
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//
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// Pointer types
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//
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template<typename _Tp>
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struct __is_pointer
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{
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enum { __value = 0 };
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typedef __false_type __type;
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};
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template<typename _Tp>
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struct __is_pointer<_Tp*>
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{
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enum { __value = 1 };
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typedef __true_type __type;
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};
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//
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// An arithmetic type is an integer type or a floating point type
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//
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template<typename _Tp>
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struct __is_arithmetic
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: public __traitor<__is_integer<_Tp>, __is_floating<_Tp> >
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{ };
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//
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// A scalar type is an arithmetic type or a pointer type
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//
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template<typename _Tp>
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struct __is_scalar
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: public __traitor<__is_arithmetic<_Tp>, __is_pointer<_Tp> >
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{ };
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//
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// For use in std::copy and std::find overloads for streambuf iterators.
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//
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template<typename _Tp>
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struct __is_char
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{
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enum { __value = 0 };
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typedef __false_type __type;
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};
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template<>
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struct __is_char<char>
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{
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enum { __value = 1 };
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typedef __true_type __type;
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};
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#ifdef __WCHAR_TYPE__
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template<>
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struct __is_char<wchar_t>
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{
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enum { __value = 1 };
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typedef __true_type __type;
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};
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#endif
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template<typename _Tp>
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struct __is_byte
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{
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enum { __value = 0 };
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typedef __false_type __type;
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};
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template<>
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struct __is_byte<char>
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{
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enum { __value = 1 };
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typedef __true_type __type;
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};
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template<>
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struct __is_byte<signed char>
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{
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enum { __value = 1 };
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typedef __true_type __type;
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};
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template<>
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struct __is_byte<unsigned char>
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{
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enum { __value = 1 };
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typedef __true_type __type;
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};
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#if __cplusplus >= 201703L
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enum class byte : unsigned char;
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template<>
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struct __is_byte<byte>
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{
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enum { __value = 1 };
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typedef __true_type __type;
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};
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#endif // C++17
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#ifdef _GLIBCXX_USE_CHAR8_T
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template<>
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struct __is_byte<char8_t>
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{
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enum { __value = 1 };
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typedef __true_type __type;
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};
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#endif
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template<typename> struct iterator_traits;
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// A type that is safe for use with memcpy, memmove, memcmp etc.
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template<typename _Tp>
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struct __is_nonvolatile_trivially_copyable
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{
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enum { __value = __is_trivially_copyable(_Tp) };
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};
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// Cannot use memcpy/memmove/memcmp on volatile types even if they are
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// trivially copyable, so ensure __memcpyable<volatile int*, volatile int*>
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// and similar will be false.
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template<typename _Tp>
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struct __is_nonvolatile_trivially_copyable<volatile _Tp>
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{
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enum { __value = 0 };
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};
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// Whether two iterator types can be used with memcpy/memmove.
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template<typename _OutputIter, typename _InputIter>
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struct __memcpyable
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{
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enum { __value = 0 };
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};
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template<typename _Tp>
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struct __memcpyable<_Tp*, _Tp*>
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: __is_nonvolatile_trivially_copyable<_Tp>
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{ };
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template<typename _Tp>
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struct __memcpyable<_Tp*, const _Tp*>
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: __is_nonvolatile_trivially_copyable<_Tp>
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{ };
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// Whether two iterator types can be used with memcmp.
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// This trait only says it's well-formed to use memcmp, not that it
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// gives the right answer for a given algorithm. So for example, std::equal
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// needs to add additional checks that the types are integers or pointers,
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// because other trivially copyable types can overload operator==.
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template<typename _Iter1, typename _Iter2>
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struct __memcmpable
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{
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enum { __value = 0 };
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};
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// OK to use memcmp with pointers to trivially copyable types.
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template<typename _Tp>
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struct __memcmpable<_Tp*, _Tp*>
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: __is_nonvolatile_trivially_copyable<_Tp>
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{ };
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template<typename _Tp>
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struct __memcmpable<const _Tp*, _Tp*>
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: __is_nonvolatile_trivially_copyable<_Tp>
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{ };
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template<typename _Tp>
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struct __memcmpable<_Tp*, const _Tp*>
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: __is_nonvolatile_trivially_copyable<_Tp>
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{ };
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// Whether memcmp can be used to determine ordering for a type
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// e.g. in std::lexicographical_compare or three-way comparisons.
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// True for unsigned integer-like types where comparing each byte in turn
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// as an unsigned char yields the right result. This is true for all
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// unsigned integers on big endian targets, but only unsigned narrow
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// character types (and std::byte) on little endian targets.
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template<typename _Tp, bool _TreatAsBytes =
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#if __BYTE_ORDER__ == __ORDER_BIG_ENDIAN__
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__is_integer<_Tp>::__value
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#else
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__is_byte<_Tp>::__value
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#endif
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>
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struct __is_memcmp_ordered
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{
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static const bool __value = _Tp(-1) > _Tp(1); // is unsigned
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};
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template<typename _Tp>
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struct __is_memcmp_ordered<_Tp, false>
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{
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static const bool __value = false;
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};
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// Whether two types can be compared using memcmp.
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template<typename _Tp, typename _Up, bool = sizeof(_Tp) == sizeof(_Up)>
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struct __is_memcmp_ordered_with
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{
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static const bool __value = __is_memcmp_ordered<_Tp>::__value
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&& __is_memcmp_ordered<_Up>::__value;
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};
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template<typename _Tp, typename _Up>
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struct __is_memcmp_ordered_with<_Tp, _Up, false>
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{
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static const bool __value = false;
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};
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#if __cplusplus >= 201703L
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#if __BYTE_ORDER__ == __ORDER_BIG_ENDIAN__
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// std::byte is not an integer, but it can be compared using memcmp.
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template<>
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struct __is_memcmp_ordered<std::byte, false>
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{ static constexpr bool __value = true; };
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#endif
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// std::byte can only be compared to itself, not to other types.
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template<>
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struct __is_memcmp_ordered_with<std::byte, std::byte, true>
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{ static constexpr bool __value = true; };
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template<typename _Tp, bool _SameSize>
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struct __is_memcmp_ordered_with<_Tp, std::byte, _SameSize>
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{ static constexpr bool __value = false; };
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template<typename _Up, bool _SameSize>
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struct __is_memcmp_ordered_with<std::byte, _Up, _SameSize>
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{ static constexpr bool __value = false; };
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#endif
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//
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// Move iterator type
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//
|
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template<typename _Tp>
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struct __is_move_iterator
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{
|
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enum { __value = 0 };
|
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typedef __false_type __type;
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};
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|
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// Fallback implementation of the function in bits/stl_iterator.h used to
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// remove the move_iterator wrapper.
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template<typename _Iterator>
|
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_GLIBCXX20_CONSTEXPR
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inline _Iterator
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__miter_base(_Iterator __it)
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{ return __it; }
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|
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_GLIBCXX_END_NAMESPACE_VERSION
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|
} // namespace
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} // extern "C++"
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|
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#endif //_CPP_TYPE_TRAITS_H
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