return previous element if visited

weed/util/skiplist/skiplist.go

@@ -67,17 +67,17 @@ func (t *SkipList) generateLevel(maxLevel int) int {
 	return level
 }
 
-func (t *SkipList) findEntryIndex(key []byte, level int) int {
+func (t *SkipList) findEntryIndex(key []byte, minLevel int) int {
 	// Find good entry point so we don't accidentally skip half the list.
 	for i := t.maxLevel; i >= 0; i-- {
-		if t.startLevels[i] != nil && bytes.Compare(t.startLevels[i].Key, key) < 0 || i <= level {
+		if t.startLevels[i] != nil && bytes.Compare(t.startLevels[i].Key, key) < 0 || i <= minLevel {
 			return i
 		}
 	}
 	return 0
 }
 
-func (t *SkipList) findExtended(key []byte, findGreaterOrEqual bool) (foundElem *SkipListElement, ok bool, err error) {
+func (t *SkipList) findExtended(key []byte, findGreaterOrEqual bool) (prevElementIfVisited *SkipListElement, foundElem *SkipListElement, ok bool, err error) {
 
 	foundElem = nil
 	ok = false
@@ -120,6 +120,7 @@ func (t *SkipList) findExtended(key []byte, findGreaterOrEqual bool) (foundElem
 
 				// Early exit
 				if currentNode.Next[0] != nil && bytes.Compare(currentNode.Next[0].Key, key) == 0 {
+					prevElementIfVisited = currentNode
 					var currentNodeNext *SkipListElement
 					currentNodeNext, err = t.loadElement(currentNode.Next[0])
 					if err != nil {
@@ -150,26 +151,26 @@ func (t *SkipList) findExtended(key []byte, findGreaterOrEqual bool) (foundElem
 // Find tries to find an element in the skiplist based on the key from the given ListElement.
 // elem can be used, if ok is true.
 // Find runs in approx. O(log(n))
-func (t *SkipList) Find(key []byte) (elem *SkipListElement, ok bool, err error) {
+func (t *SkipList) Find(key []byte) (prevIfVisited *SkipListElement, elem *SkipListElement, ok bool, err error) {
 
 	if t == nil || key == nil {
 		return
 	}
 
-	elem, ok, err = t.findExtended(key, false)
+	prevIfVisited, elem, ok, err = t.findExtended(key, false)
 	return
 }
 
 // FindGreaterOrEqual finds the first element, that is greater or equal to the given ListElement e.
 // The comparison is done on the keys (So on ExtractKey()).
 // FindGreaterOrEqual runs in approx. O(log(n))
-func (t *SkipList) FindGreaterOrEqual(key []byte) (elem *SkipListElement, ok bool, err error) {
+func (t *SkipList) FindGreaterOrEqual(key []byte) (prevIfVisited *SkipListElement, elem *SkipListElement, ok bool, err error) {
 
 	if t == nil || key == nil {
 		return
 	}
 
-	elem, ok, err = t.findExtended(key, true)
+	prevIfVisited, elem, ok, err = t.findExtended(key, true)
 	return
 }
 

weed/util/skiplist/skiplist_test.go

@@ -23,12 +23,12 @@ func TestInsertAndFind(t *testing.T) {
 
 	var listPointer *SkipList
 	listPointer.Insert(k0, k0)
-	if _, ok, _ := listPointer.Find(k0); ok {
+	if _, _, ok, _ := listPointer.Find(k0); ok {
 		t.Fail()
 	}
 
 	list = New(memStore)
-	if _, ok, _ := list.Find(k0); ok {
+	if _, _, ok, _ := list.Find(k0); ok {
 		t.Fail()
 	}
 	if !list.IsEmpty() {
@@ -42,7 +42,7 @@ func TestInsertAndFind(t *testing.T) {
 	}
 	for i := 0; i < maxN; i++ {
 		key := []byte(strconv.Itoa(maxN - i))
-		if _, ok, _ := list.Find(key); !ok {
+		if _, _, ok, _ := list.Find(key); !ok {
 			t.Fail()
 		}
 	}
@@ -55,7 +55,7 @@ func TestInsertAndFind(t *testing.T) {
 	}
 	for i := 0; i < maxN; i++ {
 		key := []byte(strconv.Itoa(i))
-		if _, ok, _ := list.Find(key); !ok {
+		if _, _, ok, _ := list.Find(key); !ok {
 			t.Fail()
 		}
 	}
@@ -71,7 +71,7 @@ func TestInsertAndFind(t *testing.T) {
 	for _, e := range rList {
 		key := []byte(strconv.Itoa(e))
 		// println("find", e)
-		if _, ok, _ := list.Find(key); !ok {
+		if _, _, ok, _ := list.Find(key); !ok {
 			t.Fail()
 		}
 	}
@@ -215,7 +215,7 @@ func TestFindGreaterOrEqual(t *testing.T) {
 	var listPointer *SkipList
 
 	// Test on empty list.
-	if _, ok, _ := listPointer.FindGreaterOrEqual(Element(0)); ok {
+	if _, _, ok, _ := listPointer.FindGreaterOrEqual(Element(0)); ok {
 		t.Fail()
 	}
 
@@ -227,7 +227,7 @@ func TestFindGreaterOrEqual(t *testing.T) {
 
 	for i := 0; i < maxN; i++ {
 		key := Element(rand.Intn(maxNumber))
-		if v, ok, _ := list.FindGreaterOrEqual(key); ok {
+		if _, v, ok, _ := list.FindGreaterOrEqual(key); ok {
 			// if f is v should be bigger than the element before
 			if v.Prev != nil && bytes.Compare(v.Prev.Key, key) >= 0 {
 				fmt.Printf("PrevV: %s\n    key: %s\n\n", string(v.Prev.Key), string(key))
@@ -261,7 +261,7 @@ func TestChangeValue(t *testing.T) {
 
 	for i := 0; i < maxN; i++ {
 		// The key only looks at the int so the string doesn't matter here!
-		f1, ok, _ := list.Find(Element(i))
+		_, f1, ok, _ := list.Find(Element(i))
 		if !ok {
 			t.Fail()
 		}
@@ -269,7 +269,7 @@ func TestChangeValue(t *testing.T) {
 		if err != nil {
 			t.Fail()
 		}
-		f2, ok, _ := list.Find(Element(i))
+		_, f2, ok, _ := list.Find(Element(i))
 		if !ok {
 			t.Fail()
 		}