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 <limits> 15 #include <type_traits> 16 17 #if !defined(_LIBCPP_HAS_NO_PRAGMA_SYSTEM_HEADER) 18 # pragma GCC system_header 19 #endif 20 21 _LIBCPP_PUSH_MACROS 22 #include <__undef_macros> 23 24 _LIBCPP_BEGIN_NAMESPACE_STD 25 26 #if _LIBCPP_STD_VER > 17 27 template <class _Tp> 28 _LIBCPP_INLINE_VISIBILITY constexpr 29 enable_if_t<is_integral_v<_Tp> && !is_same_v<bool, _Tp> && !is_null_pointer_v<_Tp>, _Tp> 30 midpoint(_Tp __a, _Tp __b) noexcept 31 _LIBCPP_DISABLE_UBSAN_UNSIGNED_INTEGER_CHECK 32 { 33 using _Up = make_unsigned_t<_Tp>; 34 constexpr _Up __bitshift = numeric_limits<_Up>::digits - 1; 35 36 _Up __diff = _Up(__b) - _Up(__a); 37 _Up __sign_bit = __b < __a; 38 39 _Up __half_diff = (__diff / 2) + (__sign_bit << __bitshift) + (__sign_bit & __diff); 40 41 return __a + __half_diff; 42 } 43 44 45 template <class _TPtr> 46 _LIBCPP_INLINE_VISIBILITY constexpr 47 enable_if_t<is_pointer_v<_TPtr> 48 && is_object_v<remove_pointer_t<_TPtr>> 49 && ! is_void_v<remove_pointer_t<_TPtr>> 50 && (sizeof(remove_pointer_t<_TPtr>) > 0), _TPtr> 51 midpoint(_TPtr __a, _TPtr __b) noexcept 52 { 53 return __a + _VSTD::midpoint(ptrdiff_t(0), __b - __a); 54 } 55 56 57 template <typename _Tp> 58 constexpr int __sign(_Tp __val) { 59 return (_Tp(0) < __val) - (__val < _Tp(0)); 60 } 61 62 template <typename _Fp> 63 constexpr _Fp __fp_abs(_Fp __f) { return __f >= 0 ? __f : -__f; } 64 65 template <class _Fp> 66 _LIBCPP_INLINE_VISIBILITY constexpr 67 enable_if_t<is_floating_point_v<_Fp>, _Fp> 68 midpoint(_Fp __a, _Fp __b) noexcept 69 { 70 constexpr _Fp __lo = numeric_limits<_Fp>::min()*2; 71 constexpr _Fp __hi = numeric_limits<_Fp>::max()/2; 72 return __fp_abs(__a) <= __hi && __fp_abs(__b) <= __hi ? // typical case: overflow is impossible 73 (__a + __b)/2 : // always correctly rounded 74 __fp_abs(__a) < __lo ? __a + __b/2 : // not safe to halve a 75 __fp_abs(__b) < __lo ? __a/2 + __b : // not safe to halve b 76 __a/2 + __b/2; // otherwise correctly rounded 77 } 78 79 #endif // _LIBCPP_STD_VER > 17 80 81 _LIBCPP_END_NAMESPACE_STD 82 83 _LIBCPP_POP_MACROS 84 85 #endif // _LIBCPP___NUMERIC_MIDPOINT_H 86