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libstdc++: define std::common_comparison_category for C++20

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* libsupc++/compare (common_comparison_category)
	(common_comparison_category_t): Define for C++20.
	* testsuite/18_support/comparisons/common/1.cc: New test.

From-SVN: r277943
This commit is contained in:
Jonathan Wakely 2019-11-08 00:37:08 +00:00 committed by Jonathan Wakely
parent 780bc8922b
commit 2966952166
3 changed files with 133 additions and 18 deletions
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4
libstdc++-v3/ChangeLog
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@ -1,5 +1,9 @@
2019-11-07 Jonathan Wakely <jwakely@redhat.com>
* libsupc++/compare (common_comparison_category)
(common_comparison_category_t): Define for C++20.
* testsuite/18_support/comparisons/common/1.cc: New test.
* include/bits/stl_algo.h (for_each_n): Handle negative count.
* testsuite/25_algorithms/for_each/for_each_n_debug.cc: New test.

67
libstdc++-v3/libsupc++/compare
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@ -385,18 +385,81 @@ namespace std
is_gteq(partial_ordering __cmp) noexcept
{ return __cmp >= 0; }
#if __cpp_lib_concepts
namespace __detail
{
template<typename _Tp>
inline constexpr unsigned __cmp_cat_id = 1;
template<>
inline constexpr unsigned __cmp_cat_id<strong_ordering> = 2;
template<>
inline constexpr unsigned __cmp_cat_id<weak_ordering> = 4;
template<>
inline constexpr unsigned __cmp_cat_id<partial_ordering> = 8;
template<typename... _Ts>
constexpr unsigned __cmp_cat_ids()
{ return (__cmp_cat_id<_Ts> | ...); }
template<unsigned>
struct __common_cmp_cat;
// If any Ti is not a comparison category type, U is void.
template<unsigned _Bits>
requires ((_Bits & 1) == 1)
struct __common_cmp_cat<_Bits> { using type = void; };
// Otherwise, if at least one Ti is std::partial_ordering,
// U is std::partial_ordering.
template<unsigned _Bits>
requires ((_Bits & 0b1001) == 0b1000)
struct __common_cmp_cat<_Bits> { using type = partial_ordering; };
// Otherwise, if at least one Ti is std::weak_ordering,
// U is std::weak_ordering.
template<unsigned _Bits>
requires ((_Bits & 0b1101) == 0b0100)
struct __common_cmp_cat<_Bits> { using type = weak_ordering; };
// Otherwise, U is std::strong_ordering.
template<>
struct __common_cmp_cat<0b0010> { using type = strong_ordering; };
} // namespace __detail
// [cmp.common], common comparison category type
template<typename... _Ts>
struct common_comparison_category
{
// using type = TODO
using type
= __detail::__common_cmp_cat<__detail::__cmp_cat_ids<_Ts...>()>::type;
};
// Partial specializations for one and zero argument cases.
template<typename _Tp>
struct common_comparison_category<_Tp>
{ using type = void; };
template<>
struct common_comparison_category<partial_ordering>
{ using type = partial_ordering; };
template<>
struct common_comparison_category<weak_ordering>
{ using type = weak_ordering; };
template<>
struct common_comparison_category<strong_ordering>
{ using type = strong_ordering; };
template<>
struct common_comparison_category<>
{ using type = strong_ordering; };
template<typename... _Ts>
using common_comparison_category_t
= typename common_comparison_category<_Ts...>::type;
#if __cpp_lib_concepts
namespace __detail
{
template<typename _Tp, typename _Cat>

48
libstdc++-v3/testsuite/18_support/comparisons/common/1.cc Normal file
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@ -0,0 +1,48 @@
// Copyright (C) 2019 Free Software Foundation, Inc.
//
// This file is part of the GNU ISO C++ Library. This library 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, or (at your option)
// any later version.
// This library 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 library; see the file COPYING3. If not see
// <http://www.gnu.org/licenses/>.
// { dg-options "-std=gnu++2a" }
// { dg-do compile { target c++2a } }
#include <compare>
template<typename Cat, typename... T>
constexpr bool check()
{
return std::same_as<Cat, std::common_comparison_category_t<T...>>;
}
using std::partial_ordering;
using std::weak_ordering;
using std::strong_ordering;
static_assert(check<strong_ordering>());
static_assert(check<void, int>());
static_assert(check<void, int, int>());
static_assert(check<void, weak_ordering, int>());
static_assert(check<void, int, partial_ordering>());
static_assert(check<partial_ordering, partial_ordering>());
static_assert(check<partial_ordering, weak_ordering, partial_ordering>());
using PO = std::partial_ordering;
using WO = std::weak_ordering;
using SO = std::strong_ordering;
static_assert(check<PO, SO, PO, SO, SO>());
static_assert(check<PO, SO, PO, SO, WO>());
static_assert(check<WO, SO, WO, SO, WO>());
static_assert(check<SO, SO, SO, SO, SO>());