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Centralize the check that the floating point implementation follows IEEE754 

C++ does not specify which kind of floating point implementation is
being used. The C Standard doesn't either, but it includes a normative
reference for implementations adoping it (ISO/IEC 9899:2011 Annex F).

There are a few existing checks in qfloat16.cpp; move them to qglobal.cpp
(next to the other, similar checks), and improve them by actually
checking that the radix used for floating point numbers is 2.

Change-Id: I704a3a8efeb51014b3be23fb236654d647a6f44f
Reviewed-by: Lars Knoll <lars.knoll@qt.io>
bb10
Giuseppe D'Angelo 2017-04-20 22:30:56 +02:00
parent 07942adb77
commit 759af3e5ad
2 changed files with 27 additions and 18 deletions
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18
src/corelib/global/qfloat16.cpp
View File

@ -59,24 +59,6 @@ QT_BEGIN_NAMESPACE
\since 5.9
*/
Q_STATIC_ASSERT_X(sizeof(float) == sizeof(quint32),
"qfloat16 assumes that floats are 32 bits wide");
// There are a few corner cases regarding denormals where GHS compiler is relying
// hardware behavior that is not IEC 559 compliant. Therefore the compiler
// reports std::numeric_limits<float>::is_iec559 as false. This is all right
// according to our needs.
#if !defined(Q_CC_GHS)
Q_STATIC_ASSERT_X(std::numeric_limits<float>::is_iec559,
"Only works with IEEE 754 floating point");
#endif
Q_STATIC_ASSERT_X(std::numeric_limits<float>::has_infinity &&
std::numeric_limits<float>::has_quiet_NaN &&
std::numeric_limits<float>::has_signaling_NaN,
"Only works with IEEE 754 floating point");
/*!
Returns true if the \c qfloat16 \a {f} is equivalent to infinity.
\relates <QFloat16>

27
src/corelib/global/qglobal.cpp
View File

@ -112,6 +112,33 @@ Q_CORE_EXPORT void *qMemSet(void *dest, int c, size_t n);
Q_STATIC_ASSERT_X(sizeof(int) == 4, "Qt assumes that int is 32 bits");
Q_STATIC_ASSERT_X(UCHAR_MAX == 255, "Qt assumes that char is 8 bits");
Q_STATIC_ASSERT_X(QT_POINTER_SIZE == sizeof(void *), "QT_POINTER_SIZE defined incorrectly");
Q_STATIC_ASSERT_X(sizeof(float) == 4, "Qt assumes that float is 32 bits");
// While we'd like to check for __STDC_IEC_559__, as per ISO/IEC 9899:2011
// Annex F (C11, normative for C++11), there are a few corner cases regarding
// denormals where GHS compiler is relying hardware behavior that is not IEC
// 559 compliant. So split the check in several subchecks.
// On GHC the compiler reports std::numeric_limits<float>::is_iec559 as false.
// This is all right according to our needs.
#if !defined(Q_CC_GHS)
Q_STATIC_ASSERT_X(std::numeric_limits<float>::is_iec559,
"Qt assumes IEEE 754 floating point");
#endif
// Technically, presence of NaN and infinities are implied from the above check,
// but double checking our environment doesn't hurt...
Q_STATIC_ASSERT_X(std::numeric_limits<float>::has_infinity &&
std::numeric_limits<float>::has_quiet_NaN &&
std::numeric_limits<float>::has_signaling_NaN,
"Qt assumes IEEE 754 floating point");
// is_iec559 checks for ISO/IEC/IEEE 60559:2011 (aka IEEE 754-2008) compliance,
// but that allows for a non-binary radix. We need to recheck that.
// Note how __STDC_IEC_559__ would instead check for IEC 60559:1989, aka
// ANSI/IEEE 754−1985, which specifically implies binary floating point numbers.
Q_STATIC_ASSERT_X(std::numeric_limits<float>::radix == 2,
"Qt assumes binary IEEE 754 floating point");
/*!
\class QFlag