Unduplicate the implementations of next power of two

Qtbase contains four identical implementations of next power of two,
these should be shared and the implementation made available to other
qt modules, as it is also used many places outside of qtbase.

[ChangeLog][QtCore][QtMath] Introduced qNextPowerOfTwo methods.

Change-Id: Id23fbe5ad6bae647b30d5a4212c0330e48a50278
Reviewed-by: Thiago Macieira <thiago.macieira@intel.com>

2 files changed, 6 insertions, 33 deletions

diff --git a/src/gui/opengl/qopengltexturecache.cpp b/src/gui/opengl/qopengltexturecache.cpp
index f4aa29ac0f..d8b44016b9 100644
--- a/src/gui/opengl/qopengltexturecache.cpp
+++ b/src/gui/opengl/qopengltexturecache.cpp
@@ -40,6 +40,7 @@
 ****************************************************************************/
 
 #include "qopengltexturecache_p.h"
+#include <qmath.h>
 #include <qopenglfunctions.h>
 #include <private/qopenglcontext_p.h>
 #include <private/qimagepixmapcleanuphooks_p.h>
@@ -129,20 +130,6 @@ GLuint QOpenGLTextureCache::bindTexture(QOpenGLContext *context, const QPixmap &
     return id;
 }
 
-// returns the highest number closest to v, which is a power of 2
-// NB! assumes 32 bit ints
-static int qt_next_power_of_two(int v)
-{
-    v--;
-    v |= v >> 1;
-    v |= v >> 2;
-    v |= v >> 4;
-    v |= v >> 8;
-    v |= v >> 16;
-    ++v;
-    return v;
-}
-
 GLuint QOpenGLTextureCache::bindTexture(QOpenGLContext *context, const QImage &image)
 {
     if (image.isNull())
@@ -164,8 +151,8 @@ GLuint QOpenGLTextureCache::bindTexture(QOpenGLContext *context, const QImage &i
         // Scale the pixmap if needed. GL textures needs to have the
         // dimensions 2^n+2(border) x 2^m+2(border), unless we're using GL
         // 2.0 or use the GL_TEXTURE_RECTANGLE texture target
-        int tx_w = qt_next_power_of_two(image.width());
-        int tx_h = qt_next_power_of_two(image.height());
+        int tx_w = qNextPowerOfTwo(image.width() - 1);
+        int tx_h = qNextPowerOfTwo(image.height() - 1);
         if (tx_w != image.width() || tx_h != image.height()) {
             img = img.scaled(tx_w, tx_h);
         }
diff --git a/src/gui/painting/qtextureglyphcache.cpp b/src/gui/painting/qtextureglyphcache.cpp
index 83edeb41a6..fb8c23835d 100644
--- a/src/gui/painting/qtextureglyphcache.cpp
+++ b/src/gui/painting/qtextureglyphcache.cpp
@@ -50,20 +50,6 @@ QT_BEGIN_NAMESPACE
 
 // #define CACHE_DEBUG
 
-// returns the highest number closest to v, which is a power of 2
-// NB! assumes 32 bit ints
-static inline int qt_next_power_of_two(int v)
-{
-    v--;
-    v |= v >> 1;
-    v |= v >> 2;
-    v |= v >> 4;
-    v |= v >> 8;
-    v |= v >> 16;
-    ++v;
-    return v;
-}
-
 int QTextureGlyphCache::calculateSubPixelPositionCount(glyph_t glyph) const
 {
     // Test 12 different subpixel positions since it factors into 3*4 so it gives
@@ -199,7 +185,7 @@ bool QTextureGlyphCache::populate(QFontEngine *fontEngine, int numGlyphs, const
         if (fontEngine->maxCharWidth() <= QT_DEFAULT_TEXTURE_GLYPH_CACHE_WIDTH)
             m_w = QT_DEFAULT_TEXTURE_GLYPH_CACHE_WIDTH;
         else
-            m_w = qt_next_power_of_two(fontEngine->maxCharWidth());
+            m_w = qNextPowerOfTwo(qCeil(fontEngine->maxCharWidth()) - 1);
     }
 
     // now actually use the coords and paint the wanted glyps into cache.
@@ -261,9 +247,9 @@ void QTextureGlyphCache::fillInPendingGlyphs()
 
     if (isNull() || requiredHeight > m_h || requiredWidth > m_w) {
         if (isNull())
-            createCache(qt_next_power_of_two(requiredWidth), qt_next_power_of_two(requiredHeight));
+            createCache(qNextPowerOfTwo(requiredWidth - 1), qNextPowerOfTwo(requiredHeight - 1));
         else
-            resizeCache(qt_next_power_of_two(requiredWidth), qt_next_power_of_two(requiredHeight));
+            resizeCache(qNextPowerOfTwo(requiredWidth - 1), qNextPowerOfTwo(requiredHeight - 1));
     }
 
     {