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 <__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