lavfi/delogo: remember left and right samples when interpolating

The left and right samples are the same for the whole line, so store
their values and don't recompute them for every iteration of "y".

This simple optimization results in a speed improvement between 15%
and 20% in my tests (depending on the logo geometry.)

Result is obviously the same.
Signed-off-by: Jean Delvare <khali@linux-fr.org>
Reviewed-by: Stefano Sabatini <stefasab@gmail.com>
Signed-off-by: Michael Niedermayer <michaelni@gmx.at>

libavfilter/vf_delogo.c

@@ -65,6 +65,7 @@ static void apply_delogo(uint8_t *dst, int dst_linesize,
     uint8_t *xdst, *xsrc;
 
     uint8_t *topleft, *botleft, *topright;
+    unsigned int left_sample, right_sample;
     int xclipl, xclipr, yclipt, yclipb;
     int logo_x1, logo_x2, logo_y1, logo_y2;
 
@@ -89,6 +90,13 @@ static void apply_delogo(uint8_t *dst, int dst_linesize,
     src += (logo_y1 + 1) * src_linesize;
 
     for (y = logo_y1+1; y < logo_y2-1; y++) {
+        left_sample = topleft[src_linesize*(y-logo_y1)]   +
+                      topleft[src_linesize*(y-logo_y1-1)] +
+                      topleft[src_linesize*(y-logo_y1+1)];
+        right_sample = topright[src_linesize*(y-logo_y1)]   +
+                       topright[src_linesize*(y-logo_y1-1)] +
+                       topright[src_linesize*(y-logo_y1+1)];
+
         for (x = logo_x1+1,
              xdst = dst+logo_x1+1,
              xsrc = src+logo_x1+1; x < logo_x2-1; x++, xdst++, xsrc++) {
@@ -100,13 +108,9 @@ static void apply_delogo(uint8_t *dst, int dst_linesize,
             weightb = (uint64_t)(x-logo_x1) * (logo_x2-1-x) * (y-logo_y1)                 * sar.num;
 
             interp =
-                (topleft[src_linesize*(y-logo_y1)]    +
-                 topleft[src_linesize*(y-logo_y1-1)]  +
-                 topleft[src_linesize*(y-logo_y1+1)]) * weightl
+                left_sample * weightl
                 +
-                (topright[src_linesize*(y-logo_y1)]    +
-                 topright[src_linesize*(y-logo_y1-1)]  +
-                 topright[src_linesize*(y-logo_y1+1)]) * weightr
+                right_sample * weightr
                 +
                 (topleft[x-logo_x1]    +
                  topleft[x-logo_x1-1]  +