libcxx/include/__random/clamp_to_integral.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___RANDOM_CLAMP_TO_INTEGRAL_H
  10 #define _LIBCPP___RANDOM_CLAMP_TO_INTEGRAL_H
  11
  12 #include <__config>
  13 #include <cmath>
  14 #include <limits>
  15
  16 #if !defined(_LIBCPP_HAS_NO_PRAGMA_SYSTEM_HEADER)
  17 #  pragma GCC system_header
  18 #endif
  19
  20 _LIBCPP_PUSH_MACROS
  21 #include <__undef_macros>
  22
  23 _LIBCPP_BEGIN_NAMESPACE_STD
  24
  25 template <class _IntT, class _FloatT,
  26     bool _FloatBigger = (numeric_limits<_FloatT>::digits > numeric_limits<_IntT>::digits),
  27     int _Bits = (numeric_limits<_IntT>::digits - numeric_limits<_FloatT>::digits)>
  28 _LIBCPP_INLINE_VISIBILITY
  29 _LIBCPP_CONSTEXPR _IntT __max_representable_int_for_float() _NOEXCEPT {
  30   static_assert(is_floating_point<_FloatT>::value, "must be a floating point type");
  31   static_assert(is_integral<_IntT>::value, "must be an integral type");
  32   static_assert(numeric_limits<_FloatT>::radix == 2, "FloatT has incorrect radix");
  33   static_assert((_IsSame<_FloatT, float>::value || _IsSame<_FloatT, double>::value
  34                  || _IsSame<_FloatT,long double>::value), "unsupported floating point type");
  35   return _FloatBigger ? numeric_limits<_IntT>::max() :  (numeric_limits<_IntT>::max() >> _Bits << _Bits);
  36 }
  37
  38 // Convert a floating point number to the specified integral type after
  39 // clamping to the integral type's representable range.
  40 //
  41 // The behavior is undefined if `__r` is NaN.
  42 template <class _IntT, class _RealT>
  43 _LIBCPP_INLINE_VISIBILITY
  44 _IntT __clamp_to_integral(_RealT __r) _NOEXCEPT {
  45   using _Lim = numeric_limits<_IntT>;
  46   const _IntT __max_val = __max_representable_int_for_float<_IntT, _RealT>();
  47   if (__r >= ::nextafter(static_cast<_RealT>(__max_val), INFINITY)) {
  48     return _Lim::max();
  49   } else if (__r <= _Lim::lowest()) {
  50     return _Lim::min();
  51   }
  52   return static_cast<_IntT>(__r);
  53 }
  54
  55 _LIBCPP_END_NAMESPACE_STD
  56
  57 _LIBCPP_POP_MACROS
  58
  59 #endif // _LIBCPP___RANDOM_CLAMP_TO_INTEGRAL_H