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Replace implementation-specific zero test with plain comparison 

Various double-to-string converters carefully omit the sign from -0.0,
for which they need to test whether the double is zero. This was
tested by a function that looked at the bytes of the double in an
endian-specific way. Packaging a comparison to zero in a function
seems to avoid the compiler warnings over double-comparison, so retain
the function but make it simpler. The only available benchmark
(QString's number_double benchmark) consistently shows a negligible
improvement in performance.

Change-Id: Id994177e21e4770ced904881d7e84a95cb727605
Reviewed-by: Thiago Macieira <thiago.macieira@intel.com>
bb10
Edward Welbourne 2021-08-31 14:38:52 +02:00
parent f266381b1b
commit f645bb8880
1 changed files with 2 additions and 7 deletions
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9
src/corelib/text/qlocale_tools_p.h
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@ -76,14 +76,9 @@ void qt_doubleToAscii(double d, QLocaleData::DoubleForm form, int precision, cha
[[nodiscard]] QByteArray qdtoAscii(double d, QLocaleData::DoubleForm form,
int precision, bool uppercase);
[[nodiscard]] inline bool isZero(double d)
[[nodiscard]] constexpr inline bool isZero(double d)
{
uchar *ch = (uchar *)&d;
if (QSysInfo::ByteOrder == QSysInfo::BigEndian) {
return !(ch[0] & 0x7F || ch[1] || ch[2] || ch[3] || ch[4] || ch[5] || ch[6] || ch[7]);
} else {
return !(ch[7] & 0x7F || ch[6] || ch[5] || ch[4] || ch[3] || ch[2] || ch[1] || ch[0]);
}
return d == 0; // Amusingly, compilers do not grumble.
}
// Enough space for the digits before the decimal separator: