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Improve the Latin1 conversion in QString a little

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First, use Qt::Uninitialized, since we're about to overwrite the memory
anyway with the new Latin 1 string.

Second, move the actual body of the conversion to a static void
function, which seems to improve code generation a little and, of
course, paves the way for the in-place conversion.

Change-Id: Iaed99ba1e52facad676510aa98443223e188d70a
Reviewed-by: Konstantin Ritt <ritt.ks@gmail.com>
Reviewed-by: Olivier Goffart <ogoffart@woboq.com>
This commit is contained in:
Thiago Macieira 2013-10-10 20:02:15 -07:00 committed by The Qt Project
parent b0afad8f0b
commit 8892e3d0fc
1 changed files with 8 additions and 7 deletions
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15
src/corelib/tools/qstring.cpp
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@ -3946,13 +3946,9 @@ static inline __m128i mergeQuestionMarks(__m128i chunk)
} }
#endif #endif
static QByteArray toLatin1_helper(const QChar *data, int length) static void toLatin1_helper(uchar *dst, const ushort *src, int length)
{ {
QByteArray ba;
if (length) { if (length) {
ba.resize(length);
const ushort *src = reinterpret_cast<const ushort *>(data);
uchar *dst = (uchar*) ba.data();
#if defined(__SSE2__) #if defined(__SSE2__)
if (length >= 16) { if (length >= 16) {
const int chunkCount = length >> 4; // divided by 16 const int chunkCount = length >> 4; // divided by 16
@ -4003,7 +3999,6 @@ static QByteArray toLatin1_helper(const QChar *data, int length)
++src; ++src;
} }
} }
return ba;
} }
QByteArray QString::toLatin1_helper(const QString &string) QByteArray QString::toLatin1_helper(const QString &string)
@ -4016,7 +4011,13 @@ QByteArray QString::toLatin1_helper(const QString &string)
QByteArray QString::toLatin1_helper(const QChar *data, int length) QByteArray QString::toLatin1_helper(const QChar *data, int length)
{ {
return QT_PREPEND_NAMESPACE(toLatin1_helper)(data, length); QByteArray ba(length, Qt::Uninitialized);
// since we own the only copy, we're going to const_cast the constData;
// that avoids an unnecessary call to detach() and expansion code that will never get used
QT_PREPEND_NAMESPACE(toLatin1_helper)(reinterpret_cast<uchar *>(const_cast<char *>(ba.constData())),
reinterpret_cast<const ushort *>(data), length);
return ba;
} }
/*! /*!