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

common/spans_test.go

@@ -9,26 +9,68 @@ import (
 	"testing"
 )
 
-func TestSpans(t *testing.T) {
+const spanItems = 3000
 
-	inp := make([]int32, 3000)
-	for i, n := 0, len(inp); i < n; i++ {
-		inp[i] = int32(i)
-	}
-	for i, n := 0, len(inp); i < n; i++ {
-		i1 := rand.Int31n(int32(n))
-		i2 := rand.Int31n(int32(n))
-		inp[i1], inp[i2] = inp[i2], inp[i1]
-	}
+func TestSpans(t *testing.T) {
 
 	sp := NewSpanPool()
 	var s *Span
-	for i, n := 0, len(inp); i < n; i++ {
+
+	for i := 0; i < spanItems; i++ {
+		s = sp.Insert(s, int32(i), 42)
+	}
+
+	if n := s.Len(); n != 1 {
+		t.Errorf("inc: Span length %d expected 1\n", n)
+		t.Errorf("spans: %s\n", s)
+	}
+
+	sp.FreeAll(s)
+
+	s = nil
+	for i := spanItems - 1; i >= 0; i-- {
+		s = sp.Insert(s, int32(i), 42)
+	}
+
+	if n := s.Len(); n != 1 {
+		t.Errorf("dec: Span length %d expected 1\n", n)
+		t.Errorf("spans: %s\n", s)
+	}
+
+	sp.FreeAll(s)
+
+	s = nil
+	for i := 0; i < spanItems/2; i++ {
+		j := spanItems - 1 - i
+		s = sp.Insert(s, int32(i), 42)
+		s = sp.Insert(s, int32(j), 21)
+	}
+
+	if n := s.Len(); n != 2 {
+		t.Errorf("two: Span length %d expected 2\n", n)
+		t.Errorf("spans: %s\n", s)
+	}
+
+	sp.FreeAll(s)
+
+	inp := make([]int32, spanItems)
+	for i := 0; i < spanItems; i++ {
+		inp[i] = int32(i)
+	}
+
+	for i := 0; i < spanItems; i++ {
+		i1 := rand.Int31n(int32(spanItems))
+		i2 := rand.Int31n(int32(spanItems))
+		inp[i1], inp[i2] = inp[i2], inp[i1]
+	}
+
+	s = nil
+	for i := 0; i < spanItems; i++ {
 		s = sp.Insert(s, inp[i], 42)
 	}
 
 	if n := s.Len(); n != 1 {
-		t.Errorf("Span length %d expected 1\n", n)
+		t.Errorf("rand: Span length %d expected 1\n", n)
 		t.Errorf("spans: %s\n", s)
 	}