xref: /openbsd-src/gnu/llvm/libcxx/include/__compare/strong_order.h (revision 4bdff4bed0e3d54e55670334c7d0077db4170f86)

//===----------------------------------------------------------------------===//
//
// Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
// See https://llvm.org/LICENSE.txt for license information.
// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
//
//===----------------------------------------------------------------------===//

#ifndef _LIBCPP___COMPARE_STRONG_ORDER
#define _LIBCPP___COMPARE_STRONG_ORDER

#include <__bit/bit_cast.h>
#include <__compare/compare_three_way.h>
#include <__compare/ordering.h>
#include <__config>
#include <__type_traits/conditional.h>
#include <__type_traits/decay.h>
#include <__utility/forward.h>
#include <__utility/priority_tag.h>
#include <cmath>
#include <cstdint>
#include <limits>

#ifndef _LIBCPP_HAS_NO_PRAGMA_SYSTEM_HEADER
#  pragma GCC system_header
#endif

_LIBCPP_PUSH_MACROS
#include <__undef_macros>

_LIBCPP_BEGIN_NAMESPACE_STD

#if _LIBCPP_STD_VER > 17

// [cmp.alg]
namespace __strong_order {
    struct __fn {
    // NOLINTBEGIN(libcpp-robust-against-adl) strong_order should use ADL, but only here
        template<class _Tp, class _Up>
            requires is_same_v<decay_t<_Tp>, decay_t<_Up>>
        _LIBCPP_HIDE_FROM_ABI static constexpr auto
        __go(_Tp&& __t, _Up&& __u, __priority_tag<2>)
            noexcept(noexcept(strong_ordering(strong_order(_VSTD::forward<_Tp>(__t), _VSTD::forward<_Up>(__u)))))
            -> decltype(      strong_ordering(strong_order(_VSTD::forward<_Tp>(__t), _VSTD::forward<_Up>(__u))))
            { return          strong_ordering(strong_order(_VSTD::forward<_Tp>(__t), _VSTD::forward<_Up>(__u))); }
    // NOLINTEND(libcpp-robust-against-adl)

        template<class _Tp, class _Up, class _Dp = decay_t<_Tp>>
            requires is_same_v<_Dp, decay_t<_Up>> && is_floating_point_v<_Dp>
        _LIBCPP_HIDE_FROM_ABI static constexpr strong_ordering
        __go(_Tp&& __t, _Up&& __u, __priority_tag<1>) noexcept
        {
            if constexpr (numeric_limits<_Dp>::is_iec559 && sizeof(_Dp) == sizeof(int32_t)) {
                int32_t __rx = _VSTD::bit_cast<int32_t>(__t);
                int32_t __ry = _VSTD::bit_cast<int32_t>(__u);
                __rx = (__rx < 0) ? (numeric_limits<int32_t>::min() - __rx - 1) : __rx;
                __ry = (__ry < 0) ? (numeric_limits<int32_t>::min() - __ry - 1) : __ry;
                return (__rx <=> __ry);
            } else if constexpr (numeric_limits<_Dp>::is_iec559 && sizeof(_Dp) == sizeof(int64_t)) {
                int64_t __rx = _VSTD::bit_cast<int64_t>(__t);
                int64_t __ry = _VSTD::bit_cast<int64_t>(__u);
                __rx = (__rx < 0) ? (numeric_limits<int64_t>::min() - __rx - 1) : __rx;
                __ry = (__ry < 0) ? (numeric_limits<int64_t>::min() - __ry - 1) : __ry;
                return (__rx <=> __ry);
            } else if (__t < __u) {
                return strong_ordering::less;
            } else if (__t > __u) {
                return strong_ordering::greater;
            } else if (__t == __u) {
                if constexpr (numeric_limits<_Dp>::radix == 2) {
                    return _VSTD::signbit(__u) <=> _VSTD::signbit(__t);
                } else {
                    // This is bullet 3 of the IEEE754 algorithm, relevant
                    // only for decimal floating-point;
                    // see https://stackoverflow.com/questions/69068075/
                    if (__t == 0 || _VSTD::isinf(__t)) {
                        return _VSTD::signbit(__u) <=> _VSTD::signbit(__t);
                    } else {
                        int __texp, __uexp;
                        (void)_VSTD::frexp(__t, &__texp);
                        (void)_VSTD::frexp(__u, &__uexp);
                        return (__t < 0) ? (__texp <=> __uexp) : (__uexp <=> __texp);
                    }
                }
            } else {
                // They're unordered, so one of them must be a NAN.
                // The order is -QNAN, -SNAN, numbers, +SNAN, +QNAN.
                bool __t_is_nan = _VSTD::isnan(__t);
                bool __u_is_nan = _VSTD::isnan(__u);
                bool __t_is_negative = _VSTD::signbit(__t);
                bool __u_is_negative = _VSTD::signbit(__u);
                using _IntType = conditional_t<
                    sizeof(__t) == sizeof(int32_t), int32_t, conditional_t<
                    sizeof(__t) == sizeof(int64_t), int64_t, void>
                >;
                if constexpr (is_same_v<_IntType, void>) {
                    static_assert(sizeof(_Dp) == 0, "std::strong_order is unimplemented for this floating-point type");
                } else if (__t_is_nan && __u_is_nan) {
                    // Order by sign bit, then by "payload bits" (we'll just use bit_cast).
                    if (__t_is_negative != __u_is_negative) {
                        return (__u_is_negative <=> __t_is_negative);
                    } else {
                        return _VSTD::bit_cast<_IntType>(__t) <=> _VSTD::bit_cast<_IntType>(__u);
                    }
                } else if (__t_is_nan) {
                    return __t_is_negative ? strong_ordering::less : strong_ordering::greater;
                } else {
                    return __u_is_negative ? strong_ordering::greater : strong_ordering::less;
                }
            }
        }

        template<class _Tp, class _Up>
            requires is_same_v<decay_t<_Tp>, decay_t<_Up>>
        _LIBCPP_HIDE_FROM_ABI static constexpr auto
        __go(_Tp&& __t, _Up&& __u, __priority_tag<0>)
            noexcept(noexcept(strong_ordering(compare_three_way()(_VSTD::forward<_Tp>(__t), _VSTD::forward<_Up>(__u)))))
            -> decltype(      strong_ordering(compare_three_way()(_VSTD::forward<_Tp>(__t), _VSTD::forward<_Up>(__u))))
            { return          strong_ordering(compare_three_way()(_VSTD::forward<_Tp>(__t), _VSTD::forward<_Up>(__u))); }

        template<class _Tp, class _Up>
        _LIBCPP_HIDE_FROM_ABI constexpr auto operator()(_Tp&& __t, _Up&& __u) const
            noexcept(noexcept(__go(_VSTD::forward<_Tp>(__t), _VSTD::forward<_Up>(__u), __priority_tag<2>())))
            -> decltype(      __go(_VSTD::forward<_Tp>(__t), _VSTD::forward<_Up>(__u), __priority_tag<2>()))
            { return          __go(_VSTD::forward<_Tp>(__t), _VSTD::forward<_Up>(__u), __priority_tag<2>()); }
    };
} // namespace __strong_order

inline namespace __cpo {
    inline constexpr auto strong_order = __strong_order::__fn{};
} // namespace __cpo

#endif // _LIBCPP_STD_VER > 17

_LIBCPP_END_NAMESPACE_STD

_LIBCPP_POP_MACROS

#endif // _LIBCPP___COMPARE_STRONG_ORDER