Optimize fallback RGB888 to RGB32 conversion

Improves the conversion from RGB888 to RGB32 on platforms without SIMD
versions. This includes the fallback used on non-neon ARM devices.

Besides image conversion the routine is also used for decoding JPEG.

On x86 this version is within 0.7x of the speed of the SSSE3 version.

Change-Id: Id131994d7c3c4f879d89e80f9d6c435bb5535ed7
Reviewed-by: Gunnar Sletta <gunnar@sletta.org>

1 files changed, 22 insertions, 2 deletions

diff --git a/tests/benchmarks/gui/image/qimageconversion/tst_qimageconversion.cpp b/tests/benchmarks/gui/image/qimageconversion/tst_qimageconversion.cpp
index d4834a04e2..2d4a453b58 100644
--- a/tests/benchmarks/gui/image/qimageconversion/tst_qimageconversion.cpp
+++ b/tests/benchmarks/gui/image/qimageconversion/tst_qimageconversion.cpp
@@ -43,6 +43,9 @@ private slots:
     void convertRgb888ToRgb32_data();
     void convertRgb888ToRgb32();
 
+    void convertRgb888ToRgbx8888_data();
+    void convertRgb888ToRgbx8888();
+
     void convertRgb32ToRgb888_data();
     void convertRgb32ToRgb888();
 
@@ -74,8 +77,8 @@ void tst_QImageConversion::convertRgb888ToRgb32_data()
     // 16 pixels, minimum for the SSSE3 implementation
     QTest::newRow("width: 16px; height: 5000px;") << generateImageRgb888(16, 5000);
 
-    // 50 pixels, more realistic use case
-    QTest::newRow("width: 50px; height: 5000px;") << generateImageRgb888(50, 5000);
+    // 200 pixels, more realistic use case
+    QTest::newRow("width: 200px; height: 5000px;") << generateImageRgb888(200, 5000);
 
     // 2000 pixels -> typical values for pictures
     QTest::newRow("width: 2000px; height: 2000px;") << generateImageRgb888(2000, 2000);
@@ -93,6 +96,23 @@ void tst_QImageConversion::convertRgb888ToRgb32()
     }
 }
 
+void tst_QImageConversion::convertRgb888ToRgbx8888_data()
+{
+    convertRgb888ToRgb32_data();
+}
+
+void tst_QImageConversion::convertRgb888ToRgbx8888()
+{
+    QFETCH(QImage, inputImage);
+
+    QBENCHMARK {
+        volatile QImage output = inputImage.convertToFormat(QImage::Format_RGBX8888);
+        // we need the volatile and the following to make sure the compiler does not do
+        // anything stupid :)
+        (void)output;
+    }
+}
+
 void tst_QImageConversion::convertRgb32ToRgb888_data()
 {
     QTest::addColumn<QImage>("inputImage");