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, 4 insertions, 1 deletions

diff --git a/src/gui/image/qxpmhandler.cpp b/src/gui/image/qxpmhandler.cpp
index ce7f7b8a0f..9c54b9ada4 100644
--- a/src/gui/image/qxpmhandler.cpp
+++ b/src/gui/image/qxpmhandler.cpp
@@ -42,6 +42,7 @@
 #ifndef QT_NO_IMAGEFORMAT_XPM
 
 #include <private/qcolor_p.h>
+#include <qbytearraymatcher.h>
 #include <qimage.h>
 #include <qmap.h>
 #include <qtextstream.h>
@@ -1041,7 +1042,9 @@ bool qt_read_xpm_image_or_array(QIODevice *device, const char * const * source,
         if ((readBytes = device->readLine(buf.data(), buf.size())) < 0)
             return false;
 
-        if (buf.indexOf("/* XPM") != 0) {
+        static Q_RELAXED_CONSTEXPR auto matcher = qMakeStaticByteArrayMatcher("/* XPM");
+
+        if (matcher.indexIn(buf) != 0) {
             while (readBytes > 0) {
                 device->ungetChar(buf.at(readBytes - 1));
                 --readBytes;