span buffers: Simplified code by throwing away cases that cannot happen. Extended unit tests with more pattern to check.

common/spans.go

@@ -90,65 +90,33 @@ func (sp *SpanPool) Insert(s *Span, pos, value int32) *Span {
 	}
 
 	head := s
-	for prev := s; s != nil; s = s.Next {
-		switch {
-		case pos < s.From: // before span
-			if pos == s.From-1 && value == s.Value { // directly neighbored
-				s.From = pos
-				// Check if a gap has to be closed.
-				if prev.To == s.From-1 && value == prev.Value {
-					prev.To = s.To
-					prev.Next = s.Next
-					sp.Free(s)
-					return head
-				}
+	for ; s != nil && pos > s.To; s = s.Next {
+		next := s.Next
+		if pos == s.To+1 && value == s.Value { // directly neighbored
+			s.To = pos
+			// Check if a gap has to be closed
+			if next != nil && next.From == s.To+1 && value == next.Value {
+				s.To = next.To
+				s.Next = next.Next
+				sp.Free(next)
 			}
-			// Extend prev?
-			if prev.To == pos-1 && value == prev.Value {
-				prev.To = pos
-				return head
-			}
-			// New between prev and current.
+			return head
+		}
+		// Extend next?
+		if next != nil && pos == next.From-1 && value == next.Value {
+			next.From = pos
+			return head
+		}
+		// Before next -> New between current and next
+		if next == nil || pos < next.From {
 			sn := sp.Alloc()
 			sn.From = pos
 			sn.To = pos
 			sn.Value = value
-			sn.Next = s
-			prev.Next = sn
-			return head
-
-		case pos > s.To: // after span
-			next := s.Next
-			if pos == s.To+1 && value == s.Value { // directly neighbored
-				s.To = pos
-				// Check if a gap has to be closed
-				if next != nil && next.From == s.To+1 && value == next.Value {
-					s.To = next.To
-					s.Next = next.Next
-					sp.Free(next)
-				}
-				return head
-			}
-			// Extend next?
-			if next != nil && pos == next.From-1 && value == next.Value {
-				next.From = pos
-				return head
-			}
-			// Before next -> New between current and next
-			if next == nil || pos < next.From {
-				sn := sp.Alloc()
-				sn.From = pos
-				sn.To = pos
-				sn.Value = value
-				sn.Next = next
-				s.Next = sn
-				return head
-			}
-
-		default: // pos in span -> do not modify.
+			sn.Next = next
+			s.Next = sn
 			return head
 		}
-		prev = s
 	}
 
 	return head