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368faacac7
This commit reverts 5aaefa51 (and also partly 7f285f48e77 and b6d75682f9, which were related to the original commit). As landed, 5aaefa51 had unintended consequences on some downstream bots and didn't have proper coverage upstream due to a few subtle things. Implementing this is something we should do in libc++, however we'll first need to address a few issues listed in https://reviews.llvm.org/D106124#3349710. Differential Revision: https://reviews.llvm.org/D120683
86 lines
2.6 KiB
C++
86 lines
2.6 KiB
C++
// -*- C++ -*-
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//===----------------------------------------------------------------------===//
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//
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// Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
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// See https://llvm.org/LICENSE.txt for license information.
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// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
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//
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//===----------------------------------------------------------------------===//
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#ifndef _LIBCPP___NUMERIC_MIDPOINT_H
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#define _LIBCPP___NUMERIC_MIDPOINT_H
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#include <__config>
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#include <limits>
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#include <type_traits>
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#if !defined(_LIBCPP_HAS_NO_PRAGMA_SYSTEM_HEADER)
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# pragma GCC system_header
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#endif
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_LIBCPP_PUSH_MACROS
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#include <__undef_macros>
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_LIBCPP_BEGIN_NAMESPACE_STD
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#if _LIBCPP_STD_VER > 17
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template <class _Tp>
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_LIBCPP_INLINE_VISIBILITY constexpr
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enable_if_t<is_integral_v<_Tp> && !is_same_v<bool, _Tp> && !is_null_pointer_v<_Tp>, _Tp>
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midpoint(_Tp __a, _Tp __b) noexcept
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_LIBCPP_DISABLE_UBSAN_UNSIGNED_INTEGER_CHECK
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{
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using _Up = make_unsigned_t<_Tp>;
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constexpr _Up __bitshift = numeric_limits<_Up>::digits - 1;
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_Up __diff = _Up(__b) - _Up(__a);
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_Up __sign_bit = __b < __a;
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_Up __half_diff = (__diff / 2) + (__sign_bit << __bitshift) + (__sign_bit & __diff);
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return __a + __half_diff;
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}
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template <class _TPtr>
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_LIBCPP_INLINE_VISIBILITY constexpr
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enable_if_t<is_pointer_v<_TPtr>
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&& is_object_v<remove_pointer_t<_TPtr>>
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&& ! is_void_v<remove_pointer_t<_TPtr>>
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&& (sizeof(remove_pointer_t<_TPtr>) > 0), _TPtr>
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midpoint(_TPtr __a, _TPtr __b) noexcept
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{
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return __a + _VSTD::midpoint(ptrdiff_t(0), __b - __a);
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}
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template <typename _Tp>
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constexpr int __sign(_Tp __val) {
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return (_Tp(0) < __val) - (__val < _Tp(0));
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}
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template <typename _Fp>
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constexpr _Fp __fp_abs(_Fp __f) { return __f >= 0 ? __f : -__f; }
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template <class _Fp>
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_LIBCPP_INLINE_VISIBILITY constexpr
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enable_if_t<is_floating_point_v<_Fp>, _Fp>
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midpoint(_Fp __a, _Fp __b) noexcept
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{
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constexpr _Fp __lo = numeric_limits<_Fp>::min()*2;
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constexpr _Fp __hi = numeric_limits<_Fp>::max()/2;
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return __fp_abs(__a) <= __hi && __fp_abs(__b) <= __hi ? // typical case: overflow is impossible
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(__a + __b)/2 : // always correctly rounded
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__fp_abs(__a) < __lo ? __a + __b/2 : // not safe to halve a
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__fp_abs(__b) < __lo ? __a/2 + __b : // not safe to halve b
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__a/2 + __b/2; // otherwise correctly rounded
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}
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#endif // _LIBCPP_STD_VER > 17
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_LIBCPP_END_NAMESPACE_STD
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_LIBCPP_POP_MACROS
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#endif // _LIBCPP___NUMERIC_MIDPOINT_H
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