fixed gaps calculations

interval.go

@@ -18,3 +18,10 @@ type ByLow []*Interval
 func (itvls ByLow) Len() int           { return len(itvls) }
 func (itvls ByLow) Swap(i, j int)      { itvls[i], itvls[j] = itvls[j], itvls[i] }
 func (itvls ByLow) Less(i, j int) bool { return itvls[i].Low < itvls[j].Low }
+
+// ByHigh implements sort.Interface for []Interval based on the High field.
+type ByHigh []*Interval
+
+func (itvls ByHigh) Len() int           { return len(itvls) }
+func (itvls ByHigh) Swap(i, j int)      { itvls[i], itvls[j] = itvls[j], itvls[i] }
+func (itvls ByHigh) Less(i, j int) bool { return itvls[i].High > itvls[j].High }