Add qPopulationCount() function, extracted from QBitArray

This functionality is used in multiple places in Qt itself, so it makes
sense to have a global function for this. This also allows to map this
onto specialized assembler instructions, should an architecture provide
them, later on.

Also added comprehensive tests, using a 4-bit lookup-table implementation
as a reference.

Change-Id: I8c4ea72cce54506ebb9fbe61141dbb5f1b7a660f
Reviewed-by: Stephen Kelly <stephen.kelly@kdab.com>

1 files changed, 3 insertions, 14 deletions

diff --git a/src/platformsupport/eglconvenience/qxlibeglintegration.cpp b/src/platformsupport/eglconvenience/qxlibeglintegration.cpp
index 58f24c0a04..80453816fc 100644
--- a/src/platformsupport/eglconvenience/qxlibeglintegration.cpp
+++ b/src/platformsupport/eglconvenience/qxlibeglintegration.cpp
@@ -41,17 +41,6 @@
 
 #include "qxlibeglintegration_p.h"
 
-static int countBits(unsigned long mask)
-{
-    int count = 0;
-    while (mask != 0) {
-        if (mask & 1)
-            ++count;
-        mask >>= 1;
-    }
-    return count;
-}
-
 VisualID QXlibEglIntegration::getCompatibleVisualId(Display *display, EGLDisplay eglDisplay, EGLConfig config)
 {
     VisualID    visualId = 0;
@@ -92,9 +81,9 @@ VisualID QXlibEglIntegration::getCompatibleVisualId(Display *display, EGLDisplay
                 return visualId;
             }
 
-            int visualRedSize = countBits(chosenVisualInfo->red_mask);
-            int visualGreenSize = countBits(chosenVisualInfo->green_mask);
-            int visualBlueSize = countBits(chosenVisualInfo->blue_mask);
+            int visualRedSize = qPopulationCount(chosenVisualInfo->red_mask);
+            int visualGreenSize = qPopulationCount(chosenVisualInfo->green_mask);
+            int visualBlueSize = qPopulationCount(chosenVisualInfo->blue_mask);
             int visualAlphaSize = -1; // Need XRender to tell us the alpha channel size
 
             bool visualMatchesConfig = false;