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 > 17
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 > 17
90 
91 _LIBCPP_END_NAMESPACE_STD
92 
93 _LIBCPP_POP_MACROS
94 
95 #endif // _LIBCPP___NUMERIC_MIDPOINT_H
96