histogram_read(): speed up calculations by 20%.

diff --git a/src/histogram.c b/src/histogram.c
index e9b18ee..6e01f5a 100644 (file)
--- a/src/histogram.c
+++ b/src/histogram.c
@@ -104,7 +104,7 @@ const gchar *histogram_label(Histogram *histogram)
 
 gulong histogram_read(Histogram *histogram, GdkPixbuf *imgpixbuf)
 {
-       gint w, h, i, j, srs, has_alpha;
+       gint w, h, i, j, srs, has_alpha, step;
        guchar *s_pix;
 
        if (!histogram) return 0;
@@ -117,25 +117,40 @@ gulong histogram_read(Histogram *histogram, GdkPixbuf *imgpixbuf)
 
        memset(histogram->histmap, 0, sizeof(histogram->histmap));
 
-       for (i = 0; i < h; i++)
+       /* code duplication is here to speed up the calculation */
+       step = 3 + !!(has_alpha);
+       if (histogram->histogram_chan == HCHAN_MAX)
                {
-               guchar *sp = s_pix + (i * srs); /* 8bit */
-               for (j = 0; j < w; j++)
+               for (i = 0; i < h; i++)
                        {
-                       histogram->histmap[sp[0] + 0 * HISTOGRAM_SIZE]++;
-                       histogram->histmap[sp[1] + 1 * HISTOGRAM_SIZE]++;
-                       histogram->histmap[sp[2] + 2 * HISTOGRAM_SIZE]++;
-                       if (histogram->histogram_chan == HCHAN_MAX)
+                       guchar *sp = s_pix + (i * srs); /* 8bit */
+                       for (j = 0; j < w; j++)
                                {
                                guchar t = sp[0];
                                if (sp[1]>t) t = sp[1];
                                if (sp[2]>t) t = sp[2];
-                               histogram->histmap[t + 3 * HISTOGRAM_SIZE]++;
+
+                               histogram->histmap[sp[0] + 0 * HISTOGRAM_SIZE]++;
+                               histogram->histmap[sp[1] + 1 * HISTOGRAM_SIZE]++;
+                               histogram->histmap[sp[2] + 2 * HISTOGRAM_SIZE]++;
+                               histogram->histmap[t + 3 * HISTOGRAM_SIZE]++;
+                               sp += step;
+                               }
+                       }
+               }
+       else
+               {
+               for (i = 0; i < h; i++)
+                       {
+                       guchar *sp = s_pix + (i * srs); /* 8bit */
+                       for (j = 0; j < w; j++)
+                               {
+                               histogram->histmap[sp[0] + 0 * HISTOGRAM_SIZE]++;
+                               histogram->histmap[sp[1] + 1 * HISTOGRAM_SIZE]++;
+                               histogram->histmap[sp[2] + 2 * HISTOGRAM_SIZE]++;
+                               histogram->histmap[3 * HISTOGRAM_SIZE + (sp[0]+sp[1]+sp[2])/3]++;
+                               sp += step;
                                }
-                       else
-                               histogram->histmap[3 * HISTOGRAM_SIZE + (sp[0]+sp[1]+sp[2])/3]++;
-                       sp += 3;
-                       if (has_alpha) sp++;
                        }
                }