func (it *Iterator) SeekToLast() {
	node, nodeData := it.db.findLast()
	it.updateState(node, nodeData)
}
SeekToLast locates the iterator to the last entry.
package memdb
import "unsafe"
type Iterator struct {
	db   *DB
	curr *node
	key  []byte
	val  []byte
}
func (db *DB) NewIterator() Iterator {
	return Iterator{
		db: db,
	}
}
func (it *Iterator) Valid() bool { return it.curr != nil }
func (it *Iterator) Key() []byte {
	return it.key
}
func (it *Iterator) Value() []byte {
	return it.val
}
func (it *Iterator) Next() {
	it.changeToAddr(it.curr.nexts[0])
}
func (it *Iterator) Prev() {
	it.changeToAddr(it.curr.prev)
}
func (it *Iterator) Seek(seekKey []byte) {
	node, nodeData, _ := it.db.findGreaterEqual(seekKey)  
	it.updateState(node, nodeData)
}
func (it *Iterator) SeekForPrev(target []byte) {
	node, nodeData, _ := it.db.findLess(target, true)  
	it.updateState(node, nodeData)
}
func (it *Iterator) SeekForExclusivePrev(target []byte) {
	node, nodeData, _ := it.db.findLess(target, false)
	it.updateState(node, nodeData)
}
func (it *Iterator) SeekToFirst() {
	node, nodeData := it.db.getNext(it.db.head.node, 0)
	it.updateState(node, nodeData)
}