Improve the median filter performance.

git-svn-id: file:///srv/caca.zoy.org/var/lib/svn/libpipi/trunk@3563 92316355-f0b4-4df1-b90c-862c8a59935f

pipi/filter/median.c

@@ -28,7 +28,13 @@
 
 static int cmpint(void const *i1, void const *i2)
 {
-    return *(double const *)i1 < *(double const *)i2;
+    /* On Linux amd64, this is 20 to 30 % faster than using a real
+     * comparison (which wouldn't work on Windows since it expects both
+     * negative and positive values), a ternary operator, or floats instead
+     * of doubles. */
+    union { int32_t i; double d; } u;
+    u.d = *(double const *)i1 - *(double const *)i2;
+    return u.i;
 }
 
 pipi_image_t *pipi_median(pipi_image_t *src, int radius)