cairooverlay: Optimize premultiplication/unpremultiplication loops

Pull in video frame fields into local variables. Without this the
compiler must assume that they could've changed on every use and read
them from memory again.

This reduces the inner loop from 6 memory reads per pixels to 4, and the
number of writes stays at 3.

diff --git a/ext/cairo/gstcairooverlay.c b/ext/cairo/gstcairooverlay.c
index b5acc12..6cea06f 100644 (file)
--- a/ext/cairo/gstcairooverlay.c
+++ b/ext/cairo/gstcairooverlay.c
@@ -230,12 +230,17 @@ static void
 gst_video_overlay_rectangle_premultiply_0 (GstVideoFrame * frame)
 {
   int i, j;
-  for (j = 0; j < GST_VIDEO_FRAME_HEIGHT (frame); ++j) {
+  int width = GST_VIDEO_FRAME_WIDTH (frame);
+  int height = GST_VIDEO_FRAME_HEIGHT (frame);
+  int stride = GST_VIDEO_FRAME_PLANE_STRIDE (frame, 0);
+  guint8 *data = GST_VIDEO_FRAME_PLANE_DATA (frame, 0);
+
+  for (j = 0; j < height; ++j) {
     guint8 *line;
 
-    line = GST_VIDEO_FRAME_PLANE_DATA (frame, 0);
-    line += GST_VIDEO_FRAME_PLANE_STRIDE (frame, 0) * j;
-    for (i = 0; i < GST_VIDEO_FRAME_WIDTH (frame); ++i) {
+    line = data;
+    line += stride * j;
+    for (i = 0; i < width; ++i) {
       int a = line[0];
       line[1] = line[1] * a / 255;
       line[2] = line[2] * a / 255;
@@ -250,12 +255,17 @@ static void
 gst_video_overlay_rectangle_premultiply_3 (GstVideoFrame * frame)
 {
   int i, j;
-  for (j = 0; j < GST_VIDEO_FRAME_HEIGHT (frame); ++j) {
+  int width = GST_VIDEO_FRAME_WIDTH (frame);
+  int height = GST_VIDEO_FRAME_HEIGHT (frame);
+  int stride = GST_VIDEO_FRAME_PLANE_STRIDE (frame, 0);
+  guint8 *data = GST_VIDEO_FRAME_PLANE_DATA (frame, 0);
+
+  for (j = 0; j < height; ++j) {
     guint8 *line;
 
-    line = GST_VIDEO_FRAME_PLANE_DATA (frame, 0);
-    line += GST_VIDEO_FRAME_PLANE_STRIDE (frame, 0) * j;
-    for (i = 0; i < GST_VIDEO_FRAME_WIDTH (frame); ++i) {
+    line = data;
+    line += stride * j;
+    for (i = 0; i < width; ++i) {
       int a = line[3];
       line[0] = line[0] * a / 255;
       line[1] = line[1] * a / 255;
@@ -290,12 +300,17 @@ static void
 gst_video_overlay_rectangle_unpremultiply_0 (GstVideoFrame * frame)
 {
   int i, j;
-  for (j = 0; j < GST_VIDEO_FRAME_HEIGHT (frame); ++j) {
+  int width = GST_VIDEO_FRAME_WIDTH (frame);
+  int height = GST_VIDEO_FRAME_HEIGHT (frame);
+  int stride = GST_VIDEO_FRAME_PLANE_STRIDE (frame, 0);
+  guint8 *data = GST_VIDEO_FRAME_PLANE_DATA (frame, 0);
+
+  for (j = 0; j < height; ++j) {
     guint8 *line;
 
-    line = GST_VIDEO_FRAME_PLANE_DATA (frame, 0);
-    line += GST_VIDEO_FRAME_PLANE_STRIDE (frame, 0) * j;
-    for (i = 0; i < GST_VIDEO_FRAME_WIDTH (frame); ++i) {
+    line = data;
+    line += stride * j;
+    for (i = 0; i < width; ++i) {
       int a = line[0];
       if (a) {
         line[1] = MIN ((line[1] * 255 + a / 2) / a, 255);
@@ -312,12 +327,17 @@ static void
 gst_video_overlay_rectangle_unpremultiply_3 (GstVideoFrame * frame)
 {
   int i, j;
-  for (j = 0; j < GST_VIDEO_FRAME_HEIGHT (frame); ++j) {
+  int width = GST_VIDEO_FRAME_WIDTH (frame);
+  int height = GST_VIDEO_FRAME_HEIGHT (frame);
+  int stride = GST_VIDEO_FRAME_PLANE_STRIDE (frame, 0);
+  guint8 *data = GST_VIDEO_FRAME_PLANE_DATA (frame, 0);
+
+  for (j = 0; j < height; ++j) {
     guint8 *line;
 
-    line = GST_VIDEO_FRAME_PLANE_DATA (frame, 0);
-    line += GST_VIDEO_FRAME_PLANE_STRIDE (frame, 0) * j;
-    for (i = 0; i < GST_VIDEO_FRAME_WIDTH (frame); ++i) {
+    line = data;
+    line += stride * j;
+    for (i = 0; i < width; ++i) {
       int a = line[3];
       if (a) {
         line[0] = MIN ((line[0] * 255 + a / 2) / a, 255);