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return previous element if visited

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This commit is contained in:
Chris Lu
2021-10-03 13:50:52 -07:00
parent 22d8684e88
commit a481c4a45e
2 changed files with 17 additions and 16 deletions
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15
weed/util/skiplist/skiplist.go
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@@ -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
}