Github user SolidWallOfCode commented on a diff in the pull request:
https://github.com/apache/trafficserver/pull/286#discussion_r38672458
--- Diff: lib/ts/Vec.h ---
@@ -964,41 +965,71 @@ qsort_Vec(C *left, C *right, bool (*lt)(C, C))
}
}
} else {
- C *i = left + 1, *j = right - 1;
- C x = *left;
- for (;;) {
- while (lt(x, *j))
- j--;
- while (i < j && lt(*i, x))
- i++;
- if (i >= j)
- break;
- C t = *i;
- *i = *j;
- *j = t;
- i++;
- j--;
+ C *center = left + ((right - left) / 2);
+ C median;
+
+ // find the median
+ if (lt(*center, *left)){ // order left and center
+ swap(center, left);
+ }
+ if (lt(*(right-1), *left)){ // order left and right
+ swap(right-1, left);
+ }
+ if (lt(*(right-1), *center)){ // order right and center
+ swap((right-1), center);
+ }
+ swap(center, right-2); // stash the median one from the right for
now
+ median = *(right-2); // and that's the median of the 3
+
+ // now partition, pivoting on the median value
+ // l ptr is +1 b/c we already put the lowest in there, ignore it for
now
+ // r ptr is -2 b/c we already put the biggest and the median there
+ C *l = left + 1, *r = right-2;
+
+ // move l and r until they have something to do
+ while (lt(median, *(r-1))) {
--- End diff --
Note the original code doesn't check the bounds because we know the `lt`
check will stop before `l < r` in any case (since !(median < median).
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