skl/skl.go
func (s *Skiplist) findNear(key []byte, less bool, allowEqual bool) (*node, bool) {
	x := s.head
	level := int(s.getHeight() - 1)
	for {
		// Assume x.key < key.
		next := s.getNext(x, level)
		if next == nil {
			// x.key < key < END OF LIST
			if level > 0 {
				// Can descend further to iterate closer to the end.
				level--
				continue
			}
			// Level=0. Cannot descend further. Let's return something that makes sense.
			if !less {
				return nil, false
			}
			// Try to return x. Make sure it is not a head node.
			if x == s.head {
				return nil, false
			}
			return x, false
		}

		nextKey := next.key(s.arena)
		cmp := y.CompareKeys(key, nextKey)
		if cmp > 0 {
			// x.key < next.key < key. We can continue to move right.
			x = next
			continue
		}
		if cmp == 0 {
			// x.key < key == next.key.
			if allowEqual {
				return next, true
			}
			if !less {
				// We want >, so go to base level to grab the next bigger note.
				return s.getNext(next, 0), false
			}
			// We want <. If not base level, we should go closer in the next level.
			if level > 0 {
				level--
				continue
			}
			// On base level. Return x.
			if x == s.head {
				return nil, false
			}
			return x, false
		}
		// cmp < 0. In other words, x.key < key < next.
		if level > 0 {
			level--
			continue
		}
		// At base level. Need to return something.
		if !less {
			return next, false
		}
		// Try to return x. Make sure it is not a head node.
		if x == s.head {
			return nil, false
		}
		return x, false
	}
}
func (s *Skiplist) findNear(key []byte, less bool, allowEqual bool) (*node, bool) {
	x := s.head
	level := int(s.getHeight() - 1)
	for {
		// Assume x.key < key.
		next := s.getNext(x, level)
		if next == nil {
			// x.key < key < END OF LIST
			if level > 0 {
				// Can descend further to iterate closer to the end.
				level--
				continue
			}
			// Level=0. Cannot descend further. Let's return something that makes sense.
			if !less {
				return nil, false
			}
			// Try to return x. Make sure it is not a head node.
			if x == s.head {
				return nil, false
			}
			return x, false
		}

		nextKey := next.key(s.arena)
		cmp := y.CompareKeys(key, nextKey)
		if cmp > 0 {
			// x.key < next.key < key. We can continue to move right.
			x = next
			continue
		}
		if cmp == 0 {
			// x.key < key == next.key.
			if allowEqual {
				return next, true
			}
			if !less {
				// We want >, so go to base level to grab the next bigger note.
				return s.getNext(next, 0), false
			}
			// We want <. If not base level, we should go closer in the next level.
			if level > 0 {
				level--
				continue
			}
			// On base level. Return x.
			if x == s.head {
				return nil, false
			}
			return x, false
		}
		// cmp < 0. In other words, x.key < key < next.
		if level > 0 {
			level--
			continue
		}
		// At base level. Need to return something.
		if !less {
			return next, false
		}
		// Try to return x. Make sure it is not a head node.
		if x == s.head {
			return nil, false
		}
		return x, false
	}
}
// findNear finds the node near to key.
// If less=true, it finds rightmost node such that node.key < key (if allowEqual=false) or
// node.key <= key (if allowEqual=true).
// If less=false, it finds leftmost node such that node.key > key (if allowEqual=false) or
// node.key >= key (if allowEqual=true).
// Returns the node found. The bool returned is true if the node has key equal to given key.