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Optimize QTextCodec::codecForUtfText a little 

Instead of doing byte comparisons, let the compiler do 16- and 32-bit
comparisons on its own.

Change-Id: If7e743cf8476463880ccfffd155f8629991b0b87
Reviewed-by: Olivier Goffart (Woboq GmbH) <ogoffart@woboq.com>
Reviewed-by: Tobias Hunger <tobias.hunger@qt.io>
bb10
Thiago Macieira 2018-10-20 21:45:10 -07:00
parent 66a2d15907
commit 99baa0d440
1 changed files with 14 additions and 14 deletions
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28
src/corelib/codecs/qtextcodec.cpp
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@ -45,8 +45,9 @@
#ifndef QT_NO_TEXTCODEC
#include "qbytearraymatcher.h"
#include "qlist.h"
#include "qendian.h"
#include "qfile.h"
#include "qlist.h"
#include "qstringlist.h"
#include "qvarlengtharray.h"
#if !defined(QT_BOOTSTRAPPED)
@ -1183,32 +1184,31 @@ QTextCodec *QTextCodec::codecForHtml(const QByteArray &ba)
QTextCodec *QTextCodec::codecForUtfText(const QByteArray &ba, QTextCodec *defaultCodec)
{
const int arraySize = ba.size();
const uchar *buf = reinterpret_cast<const uchar *>(ba.constData());
const uint bom = 0xfeff;
if (arraySize > 3) {
if ((uchar)ba[0] == 0x00
&& (uchar)ba[1] == 0x00
&& (uchar)ba[2] == 0xFE
&& (uchar)ba[3] == 0xFF)
uint uc = qFromUnaligned<uint>(buf);
if (uc == qToBigEndian(bom))
return QTextCodec::codecForMib(1018); // utf-32 be
else if ((uchar)ba[0] == 0xFF
&& (uchar)ba[1] == 0xFE
&& (uchar)ba[2] == 0x00
&& (uchar)ba[3] == 0x00)
else if (uc == qToLittleEndian(bom))
return QTextCodec::codecForMib(1019); // utf-32 le
}
if (arraySize < 2)
return defaultCodec;
if ((uchar)ba[0] == 0xfe && (uchar)ba[1] == 0xff)
ushort uc = qFromUnaligned<ushort>(buf);
if (uc == qToBigEndian(ushort(bom)))
return QTextCodec::codecForMib(1013); // utf16 be
else if ((uchar)ba[0] == 0xff && (uchar)ba[1] == 0xfe)
else if (uc == qToLittleEndian(ushort(bom)))
return QTextCodec::codecForMib(1014); // utf16 le
if (arraySize < 3)
return defaultCodec;
if ((uchar)ba[0] == 0xef
&& (uchar)ba[1] == 0xbb
&& (uchar)ba[2] == 0xbf)
static const char utf8bom[] = "\xef\xbb\xbf";
if (memcmp(buf, utf8bom, sizeof(utf8bom) - 1) == 0)
return QTextCodec::codecForMib(106); // utf-8
return defaultCodec;