libcxx/include/__cxx03/__algorithm/half_positive.h

   1 //===----------------------------------------------------------------------===//
   2 //
   3 // Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
   4 // See https://llvm.org/LICENSE.txt for license information.
   5 // SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
   6 //
   7 //===----------------------------------------------------------------------===//
   8
   9 #ifndef _LIBCPP___ALGORITHM_HALF_POSITIVE_H
  10 #define _LIBCPP___ALGORITHM_HALF_POSITIVE_H
  11
  12 #include <__cxx03/__config>
  13 #include <__cxx03/__type_traits/enable_if.h>
  14 #include <__cxx03/__type_traits/is_integral.h>
  15 #include <__cxx03/__type_traits/make_unsigned.h>
  16
  17 #if !defined(_LIBCPP_HAS_NO_PRAGMA_SYSTEM_HEADER)
  18 #  pragma GCC system_header
  19 #endif
  20
  21 _LIBCPP_BEGIN_NAMESPACE_STD
  22
  23 // Perform division by two quickly for positive integers (llvm.org/PR39129)
  24
  25 template <typename _Integral, __enable_if_t<is_integral<_Integral>::value, int> = 0>
  26 _LIBCPP_HIDE_FROM_ABI _LIBCPP_CONSTEXPR _Integral __half_positive(_Integral __value) {
  27   return static_cast<_Integral>(static_cast<__make_unsigned_t<_Integral> >(__value) / 2);
  28 }
  29
  30 template <typename _Tp, __enable_if_t<!is_integral<_Tp>::value, int> = 0>
  31 _LIBCPP_HIDE_FROM_ABI _LIBCPP_CONSTEXPR _Tp __half_positive(_Tp __value) {
  32   return __value / 2;
  33 }
  34
  35 _LIBCPP_END_NAMESPACE_STD
  36
  37 #endif // _LIBCPP___ALGORITHM_HALF_POSITIVE_H