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libstdc++: Fix for non-constexpr math_errhandling

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Use SFINAE magic to support: "It is unspecified whether math_errhandling
is a macro or an identifier with external linkage." [C Standard]

Signed-off-by: Matthias Kretz <m.kretz@gsi.de>

libstdc++-v3/ChangeLog:

	* include/experimental/bits/simd.h (__floating_point_flags): Do
	not rely on math_errhandling to expand to a constant expression.
This commit is contained in:
Matthias Kretz 2022-01-18 17:04:06 +01:00
parent 2cef99175a
commit 39f581028c
1 changed files with 21 additions and 7 deletions
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28
libstdc++-v3/include/experimental/bits/simd.h
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@ -283,20 +283,34 @@ constexpr inline bool __have_power_vmx = __have_power_vsx;
namespace __detail
{
constexpr bool __handle_fpexcept =
#ifdef math_errhandling
math_errhandling & MATH_ERREXCEPT;
#elif defined __FAST_MATH__
false;
#else
true;
// Determines _S_handle_fpexcept from math_errhandling if it is defined and expands to a constant
// expression. math_errhandling may expand to an extern symbol, in which case a constexpr value
// must be guessed.
template <int = math_errhandling>
constexpr bool __handle_fpexcept_impl(int)
{ return math_errhandling & MATH_ERREXCEPT; }
#endif
// Fallback if math_errhandling doesn't work: with fast-math assume floating-point exceptions are
// ignored, otherwise implement correct exception behavior.
constexpr bool __handle_fpexcept_impl(float)
{
#if defined __FAST_MATH__
return false;
#else
return true;
#endif
}
/// True if math functions must raise floating-point exceptions as specified by C17.
static constexpr bool _S_handle_fpexcept = __handle_fpexcept_impl(0);
constexpr std::uint_least64_t
__floating_point_flags()
{
std::uint_least64_t __flags = 0;
if constexpr (__handle_fpexcept)
if constexpr (_S_handle_fpexcept)
__flags |= 1;
#ifdef __FAST_MATH__
__flags |= 1 << 1;