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Correct handling of -qfloat16(0) 

It is finite and normal; it classifies as a zero; and it should not be > qfloat16(0).
Added tests to match.

Change-Id: I7874fb54f622b4cdf28b0894050ad3e75cf5d77c
Reviewed-by: Thiago Macieira <thiago.macieira@intel.com>
bb10
Edward Welbourne 2019-09-23 16:46:07 +02:00
parent a978d21dac
commit d448f2ecb8
3 changed files with 15 additions and 4 deletions
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2
src/corelib/global/qfloat16.cpp
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@ -155,7 +155,7 @@ QT_BEGIN_NAMESPACE
int qfloat16::fpClassify() const noexcept
{
return isInf() ? FP_INFINITE : isNaN() ? FP_NAN
: !b16 ? FP_ZERO : isNormal() ? FP_NORMAL : FP_SUBNORMAL;
: !(b16 & 0x7fff) ? FP_ZERO : isNormal() ? FP_NORMAL : FP_SUBNORMAL;
}
/*! \fn int qRound(qfloat16 value)

4
src/corelib/global/qfloat16.h
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@ -94,7 +94,7 @@ public:
static constexpr qfloat16 _limit_quiet_NaN() noexcept { return qfloat16(Wrap(0x7e00)); }
// Signalling NaN is 0x7f00
inline constexpr bool isNormal() const noexcept
{ return b16 == 0 || ((b16 & 0x7c00) && (b16 & 0x7c00) != 0x7c00); }
{ return (b16 & 0x7fff) == 0 || ((b16 & 0x7c00) && (b16 & 0x7c00) != 0x7c00); }
private:
quint16 b16;
constexpr inline explicit qfloat16(Wrap nibble) noexcept : b16(nibble.b16) {}
@ -296,7 +296,7 @@ class numeric_limits<QT_PREPEND_NAMESPACE(qfloat16)> : public numeric_limits<flo
public:
/*
Treat quint16 b16 as if it were:
uint S: 1; // b16 >> 15 (sign)
uint S: 1; // b16 >> 15 (sign); can be set for zero
uint E: 5; // (b16 >> 10) & 0x1f (offset exponent)
uint M: 10; // b16 & 0x3ff (adjusted mantissa)

13
tests/auto/corelib/global/qfloat16/tst_qfloat16.cpp
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@ -107,6 +107,7 @@ void tst_qfloat16::ltgt_data()
QTest::addColumn<float>("val2");
QTest::newRow("zero") << 0.0f << 0.0f;
QTest::newRow("-zero") << -0.0f << 0.0f;
QTest::newRow("ten") << 10.0f << 10.0f;
QTest::newRow("large") << 100000.0f << 100000.0f;
QTest::newRow("small") << 0.0000001f << 0.0000001f;
@ -405,6 +406,7 @@ void tst_qfloat16::finite_data()
QTest::addColumn<int>("mode");
QTest::newRow("zero") << qfloat16(0) << FP_ZERO;
QTest::newRow("-zero") << -qfloat16(0) << FP_ZERO;
QTest::newRow("one") << qfloat16(1) << FP_NORMAL;
QTest::newRow("-one") << qfloat16(-1) << FP_NORMAL;
QTest::newRow("ten") << qfloat16(10) << FP_NORMAL;
@ -459,6 +461,12 @@ void tst_qfloat16::limits() // See also: qNaN() and infinity()
// A few useful values:
const qfloat16 zero(0), one(1), ten(10);
// The specifics of minus zero:
// (IEEE 754 seems to want -zero < zero, but -0. == 0. and -0.f == 0.f in C++.)
QVERIFY(-zero <= zero);
QVERIFY(-zero == zero);
QVERIFY(!(-zero > zero));
// digits in the mantissa, including the implicit 1 before the binary dot at its left:
QVERIFY(qfloat16(1 << (Bounds::digits - 1)) + one > qfloat16(1 << (Bounds::digits - 1)));
QVERIFY(qfloat16(1 << Bounds::digits) + one == qfloat16(1 << Bounds::digits));
@ -523,7 +531,10 @@ void tst_qfloat16::limits() // See also: qNaN() and infinity()
QVERIFY(Bounds::denorm_min() > zero);
if (overOptimized)
QEXPECT_FAIL("", "Over-optimized on ARM", Continue);
QCOMPARE(Bounds::denorm_min() / rose, zero);
QVERIFY(Bounds::denorm_min() / rose == zero);
if (overOptimized)
QEXPECT_FAIL("", "Over-optimized on ARM", Continue);
QVERIFY(-Bounds::denorm_min() / rose == -zero);
}
QTEST_APPLESS_MAIN(tst_qfloat16)