Export optimized premultiply and unpremultiply methods

This patch optimizes the unpremultiply method further by using a
lookup table to avoid any divisions at all.

The opportunity is taken to export both premultiply and unpremultiply
since they are commonly used methods relevant to the exported QRgb type
that can be both premultiplied and unpremultipled ARGB.

[ChangeLog][QtGui][QColor] Exported highly optimized methods for
premultiply and unpremultiply of QRgb values.

Change-Id: I658bcf57b0bc73c34c1765b64617d43b63ae820b
Reviewed-by: Thiago Macieira <thiago.macieira@intel.com>
Reviewed-by: Gunnar Sletta <gunnar.sletta@jollamobile.com>

1 files changed, 4 insertions, 31 deletions

diff --git a/src/gui/painting/qdrawhelper_p.h b/src/gui/painting/qdrawhelper_p.h
index 0f98b07229..bbeb73f0af 100644
--- a/src/gui/painting/qdrawhelper_p.h
+++ b/src/gui/painting/qdrawhelper_p.h
@@ -599,14 +599,6 @@ static Q_ALWAYS_INLINE uint BYTE_MUL(uint x, uint a) {
     return (uint(t)) | (uint(t >> 24));
 }
 
-static Q_ALWAYS_INLINE uint PREMUL(uint x) {
-    uint a = x >> 24;
-    quint64 t = (((quint64(x)) | ((quint64(x)) << 24)) & 0x00ff00ff00ff00ff) * a;
-    t = (t + ((t >> 8) & 0xff00ff00ff00ff) + 0x80008000800080) >> 8;
-    t &= 0x000000ff00ff00ff;
-    return (uint(t)) | (uint(t >> 24)) | (a << 24);
-}
-
 #else // 32-bit versions
 
 static Q_ALWAYS_INLINE uint INTERPOLATE_PIXEL_256(uint x, uint a, uint y, uint b) {
@@ -639,20 +631,9 @@ static Q_ALWAYS_INLINE uint BYTE_MUL(uint x, uint a) {
 #  pragma pop
 #endif
 
-static Q_ALWAYS_INLINE uint PREMUL(uint x) {
-    uint a = x >> 24;
-    uint t = (x & 0xff00ff) * a;
-    t = (t + ((t >> 8) & 0xff00ff) + 0x800080) >> 8;
-    t &= 0xff00ff;
-
-    x = ((x >> 8) & 0xff) * a;
-    x = (x + ((x >> 8) & 0xff) + 0x80);
-    x &= 0xff00;
-    x |= t | (a << 24);
-    return x;
-}
 #endif
 
+
 #if Q_BYTE_ORDER == Q_BIG_ENDIAN
 static Q_ALWAYS_INLINE quint32 RGBA2ARGB(quint32 x) {
     quint32 rgb = x >> 8;
@@ -691,17 +672,9 @@ static Q_ALWAYS_INLINE uint BYTE_MUL_RGB16_32(uint x, uint a) {
     return t;
 }
 
-static Q_ALWAYS_INLINE uint INV_PREMUL(uint p) {
-    const uint alpha = qAlpha(p);
-    if (alpha == 255)
-        return p;
-    if (alpha == 0)
-        return 0;
-    // (p*(0x00ff00ff/alpha)) >> 16 == (p*255)/alpha for all p and alpha <= 256.
-    const uint invAlpha = 0x00ff00ffU / alpha;
-    // We add 0x8000 to get even rounding. The rounding also ensures that PREMUL(INV_PREMUL(p)) == p for all p.
-    return qRgba((qRed(p)*invAlpha + 0x8000)>>16, (qGreen(p)*invAlpha + 0x8000)>>16, (qBlue(p)*invAlpha + 0x8000)>>16, alpha);
-}
+// FIXME: Remove when all Qt modules have stopped using PREMUL and INV_PREMUL
+#define PREMUL(x) qPremultiply(x)
+#define INV_PREMUL(p) qUnpremultiply(p)
 
 struct quint24 {
     quint24(uint value);