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DO NOT MERGE: [libc++] Add __truncating_cast for safely casting float types to integers

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This is needed anytime we need to clamp an arbitrary floating point
value to an integer type.

Thanks to Eric Fiselier for the patch.

Differential Revision: https://reviews.llvm.org/D66836

git-svn-id: https://llvm.org/svn/llvm-project/libcxx/trunk@370891 91177308-0d34-0410-b5e6-96231b3b80d8
(cherry picked from commit c9ac8d533010d8915bcfdecab891fb451f71ce74)
(cherry picked from commit 4561f55204960c0b3bc4594089ddcf56e5655cad)

Bug: https://bugs.chromium.org/p/chromium/issues/detail?id=994957
Bug: http://b/139690488
Change-Id: Ibfa9f6465214466511e3d35b02eb3b77488050e7
This commit is contained in:
Louis Dionne
2019-09-04 12:48:32 +00:00
committed by Dan Albert
parent 82c0df65eb
commit baeddde44d
2 changed files with 124 additions and 0 deletions
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34
include/math.h
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@@ -1426,6 +1426,40 @@ trunc(_A1 __lcpp_x) _NOEXCEPT {return ::trunc((double)__lcpp_x);}
#endif // !(defined(_LIBCPP_MSVCRT) && ((_VC_CRT_MAJOR_VERSION-0) < 14))
_LIBCPP_BEGIN_NAMESPACE_STD
template <class _IntT, class _FloatT,
bool _FloatBigger = (numeric_limits<_FloatT>::digits > numeric_limits<_IntT>::digits),
int _Bits = (numeric_limits<_IntT>::digits - numeric_limits<_FloatT>::digits)>
_LIBCPP_INLINE_VISIBILITY
_LIBCPP_CONSTEXPR _IntT __max_representable_int_for_float() _NOEXCEPT {
static_assert(is_floating_point<_FloatT>::value, "must be a floating point type");
static_assert(is_integral<_IntT>::value, "must be an integral type");
static_assert(numeric_limits<_FloatT>::radix == 2, "FloatT has incorrect radix");
static_assert(_IsSame<_FloatT, float>::value || _IsSame<_FloatT, double>::value
|| _IsSame<_FloatT,long double>::value, "unsupported floating point type");
return _FloatBigger ? numeric_limits<_IntT>::max() : (numeric_limits<_IntT>::max() >> _Bits << _Bits);
}
// Convert a floating point number to the specified integral type after
// clamping to the integral types representable range.
//
// The behavior is undefined if `__r` is NaN.
template <class _IntT, class _RealT>
_LIBCPP_INLINE_VISIBILITY
_IntT __clamp_to_integral(_RealT __r) _NOEXCEPT {
using _Lim = std::numeric_limits<_IntT>;
const _IntT _MaxVal = std::__max_representable_int_for_float<_IntT, _RealT>();
if (__r >= ::nextafter(static_cast<_RealT>(_MaxVal), INFINITY)) {
return _Lim::max();
} else if (__r <= _Lim::lowest()) {
return _Lim::min();
}
return static_cast<_IntT>(__r);
}
_LIBCPP_END_NAMESPACE_STD
} // extern "C++"
#endif // __cplusplus