Featurize support for signaling NaN

One of our compilers for emscripten coerces all signaling NaNs to
quiet ones, so won't do any actual signaling. Anyone relying on them
to do so shall be disappointed, so it's better that they know about it
at compile-time - or, at least, have the ability to find it out.

Put the signaling NaN producers (and remaining (test) code using them)
under the control of a feature that's disabled when numeric_limits
claims double has no signaling NaN. Assume the bootstrap library
doesn't need signaling NaNs. Sadly, until C++20 <bit>, there's no
contexpr way to test that alleged signalling and quiet NaNs are
actually distinct.

Added some auto-tests for signaling NaN, including that it's distinct
from quiet NaN. Any platform on which the last fails should disable
this feature.

Task-number: QTBUG-77967
Change-Id: I57e9d14bfe276732cd313887adc9acc354d88f08
Reviewed-by: Joerg Bornemann <joerg.bornemann@qt.io>
This commit is contained in:
Edward Welbourne 2019-09-05 17:50:17 +02:00
parent 86876744f0
commit 4bd6cd1992
8 changed files with 47 additions and 3 deletions

View File

@ -484,6 +484,17 @@
]
}
},
"signaling_nan": {
"label": "Signaling NaN for doubles",
"type": "compile",
"test": {
"head": [ "#include <limits>" ],
"main": [
"using B = std::numeric_limits<double>;",
"static_assert(B::has_signaling_NaN, \"System lacks signaling NaN\");"
]
}
},
"sse2": {
"label": "SSE2 instructions",
"type": "x86Simd"
@ -1005,6 +1016,11 @@
{ "type": "define", "name": "QT_REDUCE_RELOCATIONS" }
]
},
"signaling_nan": {
"label": "Signaling NaN",
"condition": "tests.signaling_nan",
"output": [ "publicFeature" ]
},
"sse2": {
"label": "SSE2",
"condition": "(arch.i386 || arch.x86_64) && tests.sse2",

View File

@ -109,6 +109,7 @@
# define QT_FEATURE_renameat2 -1
#endif
#define QT_FEATURE_sharedmemory -1
#define QT_FEATURE_signaling_nan -1
#define QT_FEATURE_slog2 -1
#ifdef __GLIBC_PREREQ
# define QT_FEATURE_statx (__GLIBC_PREREQ(2, 28) ? 1 : -1)

View File

@ -81,11 +81,13 @@ Q_CORE_EXPORT bool qIsNaN(float f) { return qt_is_nan(f); }
*/
Q_CORE_EXPORT bool qIsFinite(float f) { return qt_is_finite(f); }
#if QT_CONFIG(signaling_nan)
/*!
Returns the bit pattern of a signalling NaN as a double.
\relates <QtGlobal>
*/
Q_CORE_EXPORT double qSNaN() { return qt_snan(); }
#endif
/*!
Returns the bit pattern of a quiet NaN as a double.

View File

@ -44,7 +44,6 @@
QT_BEGIN_NAMESPACE
Q_CORE_EXPORT Q_DECL_CONST_FUNCTION bool qIsInf(double d);
Q_CORE_EXPORT Q_DECL_CONST_FUNCTION bool qIsNaN(double d);
Q_CORE_EXPORT Q_DECL_CONST_FUNCTION bool qIsFinite(double d);
@ -53,7 +52,9 @@ Q_CORE_EXPORT Q_DECL_CONST_FUNCTION bool qIsInf(float f);
Q_CORE_EXPORT Q_DECL_CONST_FUNCTION bool qIsNaN(float f);
Q_CORE_EXPORT Q_DECL_CONST_FUNCTION bool qIsFinite(float f);
Q_CORE_EXPORT Q_DECL_CONST_FUNCTION int qFpClassify(float val);
#if QT_CONFIG(signaling_nan)
Q_CORE_EXPORT Q_DECL_CONST_FUNCTION double qSNaN();
#endif
Q_CORE_EXPORT Q_DECL_CONST_FUNCTION double qQNaN();
Q_CORE_EXPORT Q_DECL_CONST_FUNCTION double qInf();
@ -61,7 +62,9 @@ Q_CORE_EXPORT quint32 qFloatDistance(float a, float b);
Q_CORE_EXPORT quint64 qFloatDistance(double a, double b);
#define Q_INFINITY (QT_PREPEND_NAMESPACE(qInf)())
#define Q_SNAN (QT_PREPEND_NAMESPACE(qSNaN)())
#if QT_CONFIG(signaling_nan)
# define Q_SNAN (QT_PREPEND_NAMESPACE(qSNaN)())
#endif
#define Q_QNAN (QT_PREPEND_NAMESPACE(qQNaN)())
QT_END_NAMESPACE

View File

@ -133,13 +133,14 @@ Q_DECL_CONSTEXPR Q_DECL_CONST_FUNCTION static inline double qt_inf() noexcept
return std::numeric_limits<double>::infinity();
}
// Signaling NaN
#if QT_CONFIG(signaling_nan)
Q_DECL_CONSTEXPR Q_DECL_CONST_FUNCTION static inline double qt_snan() noexcept
{
Q_STATIC_ASSERT_X(std::numeric_limits<double>::has_signaling_NaN,
"platform has no definition for signaling NaN for type double");
return std::numeric_limits<double>::signaling_NaN();
}
#endif
// Quiet NaN
Q_DECL_CONSTEXPR Q_DECL_CONST_FUNCTION static inline double qt_qnan() noexcept

View File

@ -44,6 +44,9 @@ private slots:
void fuzzyCompare();
void rawNaN_data();
void rawNaN();
#if QT_CONFIG(signaling_nan)
void distinctNaN();
#endif
void generalNaN_data();
void generalNaN();
void infinity();
@ -139,6 +142,9 @@ void tst_QNumeric::rawNaN_data()
QTest::addColumn<double>("nan");
QTest::newRow("quiet") << qQNaN();
#if QT_CONFIG(signaling_nan)
QTest::newRow("signaling") << qSNaN();
#endif
}
void tst_QNumeric::rawNaN()
@ -147,6 +153,15 @@ void tst_QNumeric::rawNaN()
checkNaN(nan);
}
#if QT_CONFIG(signaling_nan)
void tst_QNumeric::distinctNaN()
{
const double qnan = qQNaN();
const double snan = qSNaN();
QVERIFY(memcmp(&qnan, &snan, sizeof(double)) != 0);
}
#endif
void tst_QNumeric::generalNaN_data()
{
QTest::addColumn<int>("most");

View File

@ -1413,10 +1413,12 @@ void tst_QCborValue::toCbor_data()
// The rest of these tests are conversions whose decoding does not yield
// back the same QCborValue.
#if QT_CONFIG(signaling_nan)
// Signalling NaN get normalized to quiet ones
QTest::newRow("Double:snan") << QCborValue(qSNaN()) << raw("\xfb\x7f\xf8\0""\0\0\0\0\0") << QCborValue::EncodingOptions();
QTest::newRow("Float:snan") << QCborValue(qSNaN()) << raw("\xfa\x7f\xc0\0\0") << QCborValue::EncodingOptions(QCborValue::UseFloat);
QTest::newRow("Float16:snan") << QCborValue(qSNaN()) << raw("\xf9\x7e\0") << QCborValue::EncodingOptions(QCborValue::UseFloat16);
#endif
// Floating point written as integers are read back as integers
QTest::newRow("UseInteger:0") << QCborValue(0.) << raw("\x00") << QCborValue::EncodingOptions(QCborValue::UseIntegers);

View File

@ -88,7 +88,9 @@ private slots:
void testToFillPolygons();
#if QT_CONFIG(signaling_nan)
void testNaNandInfinites();
#endif
void closing();
@ -1228,6 +1230,7 @@ void tst_QPainterPath::testToFillPolygons()
QCOMPARE(polygons.first().count(QPointF(70, 50)), 0);
}
#if QT_CONFIG(signaling_nan)
void tst_QPainterPath::testNaNandInfinites()
{
QPainterPath path1;
@ -1271,6 +1274,7 @@ void tst_QPainterPath::testNaNandInfinites()
path1.lineTo(QPointF(1, 1));
QVERIFY(path1 != path2);
}
#endif // signaling_nan
void tst_QPainterPath::connectPathDuplicatePoint()
{