1 // -*- C++ -*- 2 //===----------------------------------------------------------------------===// 3 // 4 // Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions. 5 // See https://llvm.org/LICENSE.txt for license information. 6 // SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception 7 // 8 //===----------------------------------------------------------------------===// 9 10 #ifndef _LIBCPP___NUMERIC_MIDPOINT_H 11 #define _LIBCPP___NUMERIC_MIDPOINT_H 12 13 #include <__config> 14 #include <__type_traits/enable_if.h> 15 #include <__type_traits/is_floating_point.h> 16 #include <__type_traits/is_integral.h> 17 #include <__type_traits/is_null_pointer.h> 18 #include <__type_traits/is_object.h> 19 #include <__type_traits/is_pointer.h> 20 #include <__type_traits/is_same.h> 21 #include <__type_traits/is_void.h> 22 #include <__type_traits/make_unsigned.h> 23 #include <__type_traits/remove_pointer.h> 24 #include <cstddef> 25 #include <limits> 26 27 #if !defined(_LIBCPP_HAS_NO_PRAGMA_SYSTEM_HEADER) 28 # pragma GCC system_header 29 #endif 30 31 _LIBCPP_PUSH_MACROS 32 #include <__undef_macros> 33 34 _LIBCPP_BEGIN_NAMESPACE_STD 35 36 #if _LIBCPP_STD_VER >= 20 37 template <class _Tp> 38 _LIBCPP_HIDE_FROM_ABI constexpr enable_if_t<is_integral_v<_Tp> && !is_same_v<bool, _Tp> && !is_null_pointer_v<_Tp>, _Tp> 39 midpoint(_Tp __a, _Tp __b) noexcept _LIBCPP_DISABLE_UBSAN_UNSIGNED_INTEGER_CHECK { 40 using _Up = make_unsigned_t<_Tp>; 41 constexpr _Up __bitshift = numeric_limits<_Up>::digits - 1; 42 43 _Up __diff = _Up(__b) - _Up(__a); 44 _Up __sign_bit = __b < __a; 45 46 _Up __half_diff = (__diff / 2) + (__sign_bit << __bitshift) + (__sign_bit & __diff); 47 48 return __a + __half_diff; 49 } 50 51 template <class _Tp, enable_if_t<is_object_v<_Tp> && !is_void_v<_Tp> && (sizeof(_Tp) > 0), int> = 0> 52 _LIBCPP_HIDE_FROM_ABI constexpr _Tp* midpoint(_Tp* __a, _Tp* __b) noexcept { 53 return __a + std::midpoint(ptrdiff_t(0), __b - __a); 54 } 55 56 template <typename _Tp> 57 _LIBCPP_HIDE_FROM_ABI constexpr int __sign(_Tp __val) { 58 return (_Tp(0) < __val) - (__val < _Tp(0)); 59 } 60 61 template <typename _Fp> 62 _LIBCPP_HIDE_FROM_ABI constexpr _Fp __fp_abs(_Fp __f) { 63 return __f >= 0 ? __f : -__f; 64 } 65 66 template <class _Fp> 67 _LIBCPP_HIDE_FROM_ABI constexpr enable_if_t<is_floating_point_v<_Fp>, _Fp> midpoint(_Fp __a, _Fp __b) noexcept { 68 constexpr _Fp __lo = numeric_limits<_Fp>::min() * 2; 69 constexpr _Fp __hi = numeric_limits<_Fp>::max() / 2; 70 return std::__fp_abs(__a) <= __hi && std::__fp_abs(__b) <= __hi 71 ? // typical case: overflow is impossible 72 (__a + __b) / 2 73 : // always correctly rounded 74 std::__fp_abs(__a) < __lo ? __a + __b / 2 : // not safe to halve a 75 std::__fp_abs(__b) < __lo ? __a / 2 + __b 76 : // not safe to halve b 77 __a / 2 + __b / 2; // otherwise correctly rounded 78 } 79 80 #endif // _LIBCPP_STD_VER >= 20 81 82 _LIBCPP_END_NAMESPACE_STD 83 84 _LIBCPP_POP_MACROS 85 86 #endif // _LIBCPP___NUMERIC_MIDPOINT_H 87