optimize end of row check for images

Doing profiles reveals that the check for "is this pixel at end of row?"

  if ((cur_pix + 1 - lines) % width == 0)

leads to 2 divisions, one to compute (cur_pix + 1 - lines) (divided by
sizeof(*cur_pix) which could be 3) and one for (x % width).
Although the substituted code looks more long is faster as it does not
involve divisions.

Signed-off-by: Frediano Ziglio <fziglio@redhat.com>

1 files changed, 7 insertions, 2 deletions

diff --git a/server/spice-bitmap-utils.tmpl.c b/server/spice-bitmap-utils.tmpl.c
index a104cb27..7033476b 100644
--- a/server/spice-bitmap-utils.tmpl.c
+++ b/server/spice-bitmap-utils.tmpl.c
@@ -118,7 +118,8 @@ static void FNAME(compute_lines_gradual_score)(PIXEL *lines, int width, int num_
                                                double *o_samples_sum_score, int *o_num_samples)
 {
     int jump = (SAMPLE_JUMP % width) ? SAMPLE_JUMP : SAMPLE_JUMP - 1;
-    PIXEL *cur_pix = lines + width / 2;
+    int cur_x = width / 2;
+    PIXEL *cur_pix = lines + cur_x;
     PIXEL *bottom_pix;
     PIXEL *last_line = lines + (num_lines - 1) * width;
     int num_samples = 0;
@@ -131,13 +132,17 @@ static void FNAME(compute_lines_gradual_score)(PIXEL *lines, int width, int num_
     }
 
     while (cur_pix < last_line) {
-        if ((cur_pix + 1 - lines) % width == 0) { // last pixel in the row
+        if (cur_x + 1 == width) { // last pixel in the row
             cur_pix--; // jump is bigger than 1 so we will not enter endless loop
+            cur_x--;
         }
         bottom_pix = cur_pix + width;
         samples_sum_score += FNAME(pixels_square_score)(cur_pix, bottom_pix);
         num_samples++;
         cur_pix += jump;
+        cur_x += jump;
+        while (cur_x >= width)
+            cur_x -= width;
     }
 
     (*o_samples_sum_score) = samples_sum_score;