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