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_INLINE_VISIBILITY constexpr 39 enable_if_t<is_integral_v<_Tp> && !is_same_v<bool, _Tp> && !is_null_pointer_v<_Tp>, _Tp> 40 midpoint(_Tp __a, _Tp __b) noexcept 41 _LIBCPP_DISABLE_UBSAN_UNSIGNED_INTEGER_CHECK 42 { 43 using _Up = make_unsigned_t<_Tp>; 44 constexpr _Up __bitshift = numeric_limits<_Up>::digits - 1; 45 46 _Up __diff = _Up(__b) - _Up(__a); 47 _Up __sign_bit = __b < __a; 48 49 _Up __half_diff = (__diff / 2) + (__sign_bit << __bitshift) + (__sign_bit & __diff); 50 51 return __a + __half_diff; 52 } 53 54 55 template <class _TPtr> 56 _LIBCPP_INLINE_VISIBILITY constexpr 57 enable_if_t<is_pointer_v<_TPtr> 58 && is_object_v<remove_pointer_t<_TPtr>> 59 && ! is_void_v<remove_pointer_t<_TPtr>> 60 && (sizeof(remove_pointer_t<_TPtr>) > 0), _TPtr> 61 midpoint(_TPtr __a, _TPtr __b) noexcept 62 { 63 return __a + _VSTD::midpoint(ptrdiff_t(0), __b - __a); 64 } 65 66 67 template <typename _Tp> 68 _LIBCPP_HIDE_FROM_ABI constexpr int __sign(_Tp __val) { 69 return (_Tp(0) < __val) - (__val < _Tp(0)); 70 } 71 72 template <typename _Fp> 73 _LIBCPP_HIDE_FROM_ABI constexpr _Fp __fp_abs(_Fp __f) { return __f >= 0 ? __f : -__f; } 74 75 template <class _Fp> 76 _LIBCPP_INLINE_VISIBILITY constexpr 77 enable_if_t<is_floating_point_v<_Fp>, _Fp> 78 midpoint(_Fp __a, _Fp __b) noexcept 79 { 80 constexpr _Fp __lo = numeric_limits<_Fp>::min()*2; 81 constexpr _Fp __hi = numeric_limits<_Fp>::max()/2; 82 return std::__fp_abs(__a) <= __hi && std::__fp_abs(__b) <= __hi ? // typical case: overflow is impossible 83 (__a + __b)/2 : // always correctly rounded 84 std::__fp_abs(__a) < __lo ? __a + __b/2 : // not safe to halve a 85 std::__fp_abs(__b) < __lo ? __a/2 + __b : // not safe to halve b 86 __a/2 + __b/2; // otherwise correctly rounded 87 } 88 89 #endif // _LIBCPP_STD_VER >= 20 90 91 _LIBCPP_END_NAMESPACE_STD 92 93 _LIBCPP_POP_MACROS 94 95 #endif // _LIBCPP___NUMERIC_MIDPOINT_H 96