QtBase: use new QStaticByteArrayMatcher where applicable

Even for compilers that don't yet support C++14 constexpr,
this should improve performance of searches a lot, if,
indeed, Boyer-Moore still is an optimization over linear
searching at all in these days of hardware prefetchers
and deep CPU pipelines, because the setup cost is only
incurred once. As function-statics, we also don't care
about startup ordering and cost.

It's a pity that the platform that would benefit the most
- Windows - doesn't have constexpr support, yet.

Change-Id: I827df135854fd6fbd6546e248dc37ef0fbaf1792
Reviewed-by: Friedemann Kleint <Friedemann.Kleint@qt.io>
Reviewed-by: Milian Wolff <milian.wolff@kdab.com>

1 files changed, 5 insertions, 2 deletions

diff --git a/src/corelib/codecs/qtextcodec.cpp b/src/corelib/codecs/qtextcodec.cpp
index d9c092bb4c..4f0cd914ca 100644
--- a/src/corelib/codecs/qtextcodec.cpp
+++ b/src/corelib/codecs/qtextcodec.cpp
@@ -43,6 +43,7 @@
 
 #ifndef QT_NO_TEXTCODEC
 
+#include "qbytearraymatcher.h"
 #include "qlist.h"
 #include "qfile.h"
 #include "qstringlist.h"
@@ -1092,10 +1093,12 @@ QTextCodec *QTextCodec::codecForHtml(const QByteArray &ba, QTextCodec *defaultCo
     // determine charset
     QTextCodec *c = QTextCodec::codecForUtfText(ba, 0);
     if (!c) {
+        static Q_RELAXED_CONSTEXPR auto matcher = qMakeStaticByteArrayMatcher("meta ");
         QByteArray header = ba.left(1024).toLower();
-        int pos = header.indexOf("meta ");
+        int pos = matcher.indexIn(header);
         if (pos != -1) {
-            pos = header.indexOf("charset=", pos);
+            static Q_RELAXED_CONSTEXPR auto matcher = qMakeStaticByteArrayMatcher("charset=");
+            pos = matcher.indexIn(header, pos);
             if (pos != -1) {
                 pos += qstrlen("charset=");