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_HIDE_FROM_ABI constexpr enable_if_t<is_integral_v<_Tp> && !is_same_v<bool, _Tp> && !is_null_pointer_v<_Tp>, _Tp>
  39 midpoint(_Tp __a, _Tp __b) noexcept _LIBCPP_DISABLE_UBSAN_UNSIGNED_INTEGER_CHECK {
  40   using _Up                = make_unsigned_t<_Tp>;
  41   constexpr _Up __bitshift = numeric_limits<_Up>::digits - 1;
  42
  43   _Up __diff     = _Up(__b) - _Up(__a);
  44   _Up __sign_bit = __b < __a;
  45
  46   _Up __half_diff = (__diff / 2) + (__sign_bit << __bitshift) + (__sign_bit & __diff);
  47
  48   return __a + __half_diff;
  49 }
  50
  51 template <class _Tp, enable_if_t<is_object_v<_Tp> && !is_void_v<_Tp> && (sizeof(_Tp) > 0), int> = 0>
  52 _LIBCPP_HIDE_FROM_ABI constexpr _Tp* midpoint(_Tp* __a, _Tp* __b) noexcept {
  53   return __a + std::midpoint(ptrdiff_t(0), __b - __a);
  54 }
  55
  56 template <typename _Tp>
  57 _LIBCPP_HIDE_FROM_ABI constexpr int __sign(_Tp __val) {
  58   return (_Tp(0) < __val) - (__val < _Tp(0));
  59 }
  60
  61 template <typename _Fp>
  62 _LIBCPP_HIDE_FROM_ABI constexpr _Fp __fp_abs(_Fp __f) {
  63   return __f >= 0 ? __f : -__f;
  64 }
  65
  66 template <class _Fp>
  67 _LIBCPP_HIDE_FROM_ABI constexpr enable_if_t<is_floating_point_v<_Fp>, _Fp> midpoint(_Fp __a, _Fp __b) noexcept {
  68   constexpr _Fp __lo = numeric_limits<_Fp>::min() * 2;
  69   constexpr _Fp __hi = numeric_limits<_Fp>::max() / 2;
  70   return std::__fp_abs(__a) <= __hi && std::__fp_abs(__b) <= __hi
  71            ? // typical case: overflow is impossible
  72              (__a + __b) / 2
  73            :                                             // always correctly rounded
  74              std::__fp_abs(__a) < __lo ? __a + __b / 2 : // not safe to halve a
  75                  std::__fp_abs(__b) < __lo ? __a / 2 + __b
  76                                            : // not safe to halve b
  77                  __a / 2 + __b / 2;          // otherwise correctly rounded
  78 }
  79
  80 #endif // _LIBCPP_STD_VER >= 20
  81
  82 _LIBCPP_END_NAMESPACE_STD
  83
  84 _LIBCPP_POP_MACROS
  85
  86 #endif // _LIBCPP___NUMERIC_MIDPOINT_H