libcxx/include/__numeric/midpoint.h

   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