Minor rtree package cleanup

These are just some minor fixes that were identified while working on
unrelated parts of the `rtree` package.

rtree/bulk.go

@@ -188,20 +188,11 @@ func quickPartition(items []BulkItem, k int, horizontal bool) {
 }
 
 func itemsAreHorizontal(items []BulkItem) bool {
-	// fastMin and fastMax are used rather than Box's combine method to avoid
-	// math.Min and math.Max calls (which are more expensive).
-	minX := items[0].Box.MinX
-	maxX := items[0].Box.MaxX
-	minY := items[0].Box.MinY
-	maxY := items[0].Box.MaxY
+	box := items[0].Box
 	for _, item := range items[1:] {
-		box := item.Box
-		minX = fastMin(minX, box.MinX)
-		maxX = fastMax(maxX, box.MaxX)
-		minY = fastMin(minY, box.MinY)
-		maxY = fastMax(maxY, box.MaxY)
+		box = combine(box, item.Box)
 	}
-	return maxX-minX > maxY-minY
+	return box.MaxX-box.MinX > box.MaxY-box.MinY
 }
 
 // fastMin is a faster but not functionally identical version of math.Min.

rtree/nearest.go

@@ -16,11 +16,11 @@ func (t *RTree) Nearest(box Box) (recordID int, found bool) {
 }
 
 // PrioritySearch iterates over the records in the RTree in priority order of
-// distance from the input box (shortest distanace first using the Euclidean
+// distance from the input box (shortest distance first using the Euclidean
 // metric).  The callback is called for every element iterated over. If an
 // error is returned from the callback, then iteration stops immediately. Any
 // error returned from the callback is returned by PrioritySearch, except for
-// the case where the special Stop sentinal error is returned (in which case
+// the case where the special Stop sentinel error is returned (in which case
 // nil will be returned from PrioritySearch).
 func (t *RTree) PrioritySearch(box Box, callback func(recordID int) error) error {
 	if t.root == nil {
@@ -61,9 +61,9 @@ func (q *entriesQueue) Len() int {
 }
 
 func (q *entriesQueue) Less(i int, j int) bool {
-	e1 := q.entries[i]
-	e2 := q.entries[j]
-	return squaredEuclideanDistance(e1.box, q.origin) < squaredEuclideanDistance(e2.box, q.origin)
+	d1 := squaredEuclideanDistance(q.entries[i].box, q.origin)
+	d2 := squaredEuclideanDistance(q.entries[j].box, q.origin)
+	return d1 < d2
 }
 
 func (q *entriesQueue) Swap(i int, j int) {

rtree/rtree_test.go

@@ -174,7 +174,8 @@ func checkInvariants(t *testing.T, rt *RTree, boxes []Box) {
 				t.Fatal("entry past numEntries is not the zero value")
 			}
 		}
-		if current.numEntries > maxChildren || (current != rt.root && current.numEntries < minChildren) {
+		if current.numEntries > maxChildren ||
+			(current != rt.root && current.numEntries < minChildren) {
 			t.Fatalf("%p: unexpected number of entries", current)
 		}
 	}