[gtk+/gtk-3-16] gtkcairoblur: Unroll inner loop for common radius values

[Matthias Clasen <matthiasc src gnome org>]

commit c96df5a3507a24cb270f26b4e48bd9838211ed1d
Author: Alexander Larsson <alexl redhat com>
Date:   Thu Mar 19 16:29:32 2015 +0100

    gtkcairoblur: Unroll inner loop for common radius values
    
    This unrolls the inner blur loop for radius 1-10, allowing
    the compiler to use a divide-by-constant operation instead
    of a generic division.
    
    Here is the blur-performance output before:
    
    Radius  1: 124.95 msec, 32.01 kpixels/msec:
    Radius  2: 117.27 msec, 34.11 kpixels/msec:
    Radius  3: 123.57 msec, 32.37 kpixels/msec:
    Radius  4: 118.17 msec, 33.85 kpixels/msec:
    Radius  5: 119.32 msec, 33.52 kpixels/msec:
    Radius  6: 124.17 msec, 32.21 kpixels/msec:
    Radius  7: 121.04 msec, 33.05 kpixels/msec:
    Radius  8: 130.64 msec, 30.62 kpixels/msec:
    Radius  9: 119.47 msec, 33.48 kpixels/msec:
    Radius 10: 117.95 msec, 33.91 kpixels/msec:
    Radius 11: 122.38 msec, 32.68 kpixels/msec:
    Radius 12: 121.92 msec, 32.81 kpixels/msec:
    Radius 13: 125.45 msec, 31.89 kpixels/msec:
    Radius 14: 121.63 msec, 32.89 kpixels/msec:
    Radius 15: 120.18 msec, 33.28 kpixels/msec:
    
    And after:
    
    Radius  1: 42.26 msec, 94.65 kpixels/msec:
    Radius  2: 59.15 msec, 67.62 kpixels/msec:
    Radius  3: 60.29 msec, 66.35 kpixels/msec:
    Radius  4: 64.53 msec, 61.99 kpixels/msec:
    Radius  5: 60.07 msec, 66.59 kpixels/msec:
    Radius  6: 62.43 msec, 64.07 kpixels/msec:
    Radius  7: 60.36 msec, 66.27 kpixels/msec:
    Radius  8: 59.59 msec, 67.13 kpixels/msec:
    Radius  9: 76.17 msec, 52.51 kpixels/msec:
    Radius 10: 79.41 msec, 50.37 kpixels/msec:
    Radius 11: 118.92 msec, 33.64 kpixels/msec:
    Radius 12: 121.31 msec, 32.97 kpixels/msec:
    Radius 13: 118.30 msec, 33.81 kpixels/msec:
    Radius 14: 116.82 msec, 34.24 kpixels/msec:
    Radius 15: 116.99 msec, 34.19 kpixels/msec:
    
    I.e. almost double performance for the unrolled radius values.
    
    https://bugzilla.gnome.org/show_bug.cgi?id=746468

 gtk/gtkcairoblur.c |   39 +++++++++++++++++++++++++++++----------
 1 files changed, 29 insertions(+), 10 deletions(-)
---
diff --git a/gtk/gtkcairoblur.c b/gtk/gtkcairoblur.c
index 82f5d33..170f460 100644
--- a/gtk/gtkcairoblur.c
+++ b/gtk/gtkcairoblur.c
@@ -73,18 +73,37 @@ blur_xspan (guchar *row,
    * only divide down after all three passes. (SSE parallel implementation
    * of the divide step is possible.)
    */
-  for (i = -d + offset; i < row_width + offset; i++)
-    {
-      if (i >= 0 && i < row_width)
-        sum += row[i];
-
-      if (i >= offset)
-        {
-          if (i >= d)
-            sum -= row[i - d];
 
-          tmp_buffer[i - offset] = (sum + d / 2) / d;
-        }
+#define BLUR_ROW_KERNEL(D)                                      \
+  for (i = -(D) + offset; i < row_width + offset; i++)         \
+    {                                                           \
+      if (i >= 0 && i < row_width)                              \
+        sum += row[i];                                          \
+                                                                \
+      if (i >= offset)                                         \
+       {                                                       \
+         if (i >= (D))                                         \
+           sum -= row[i - (D)];                                \
+                                                                \
+         tmp_buffer[i - offset] = (sum + (D) / 2) / (D);       \
+       }                                                       \
+    }                                                          \
+  break;
+
+  /* We unroll the values for d for radius 2-10 to avoid a generic
+   * divide operation (not radius 1, because its a no-op) */
+  switch (d)
+    {
+    case get_box_filter_size (2): BLUR_ROW_KERNEL (get_box_filter_size (2));
+    case get_box_filter_size (3): BLUR_ROW_KERNEL (get_box_filter_size (3));
+    case get_box_filter_size (4): BLUR_ROW_KERNEL (get_box_filter_size (4));
+    case get_box_filter_size (5): BLUR_ROW_KERNEL (get_box_filter_size (5));
+    case get_box_filter_size (6): BLUR_ROW_KERNEL (get_box_filter_size (6));
+    case get_box_filter_size (7): BLUR_ROW_KERNEL (get_box_filter_size (7));
+    case get_box_filter_size (8): BLUR_ROW_KERNEL (get_box_filter_size (8));
+    case get_box_filter_size (9): BLUR_ROW_KERNEL (get_box_filter_size (9));
+    case get_box_filter_size (10): BLUR_ROW_KERNEL (get_box_filter_size (10));
+    default: BLUR_ROW_KERNEL (d);
     }
 
   memcpy (row, tmp_buffer, row_width);