/** finds median in unsorted set by sorting only minimum required */
static
f_pixel get_median(const box* b, hist_item achv[])
{
const uint median_start = (b->colors-1)/2;
hist_item_sort_range(&(achv[b->ind]), b->colors,
median_start,
b->colors&1 ? 1 : 2);
if (b->colors&1) return achv[b->ind + median_start].acolor;
return averagepixels(2, &achv[b->ind + median_start], 1.0);
}
/** finds median in unsorted set by sorting only minimum required */
static f_pixel get_median(const struct box *b, hist_item achv[])
{
const unsigned int median_start = (b->colors-1)/2;
hist_item_sort_range(&(achv[b->ind]), b->colors,
median_start);
if (b->colors&1) return achv[b->ind + median_start].acolor;
// technically the second color is not guaranteed to be sorted correctly
// but most of the time it is good enough to be useful
return averagepixels(2, &achv[b->ind + median_start], 1.0, (f_pixel){0.5,0.5,0.5,0.5});
}
/** this is a simple qsort that completely sorts only elements between sort_start and +sort_len. Used to find median of the set. */
static void hist_item_sort_range(hist_item *base, unsigned int len, int sort_start, const int sort_len)
{
do {
const unsigned int l = qsort_partition(base, len), r = l+1;
if (sort_start+sort_len > 0 && (signed)l >= sort_start && l > 0) {
hist_item_sort_range(base, l, sort_start, sort_len);
}
if (len > r && r < sort_start+sort_len && (signed)len > sort_start) {
base += r; len -= r; sort_start -= r; // tail-recursive "call"
} else return;
} while(1);
}