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faster SkipList.find

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Simon Cruanes 2013-03-23 01:45:46 +01:00
parent 6f455c7cb1
commit 9788d108e3
1 changed files with 21 additions and 8 deletions
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29
skipList.ml
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@ -25,6 +25,9 @@ OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
(** {1 Imperative skip-list} *) (** {1 Imperative skip-list} *)
(** Most functions are inspired from
"A skip list cookbook", William Pugh, 1989. *)
type ('a, 'b) t = { type ('a, 'b) t = {
mutable data : ('a, 'b) bucket; mutable data : ('a, 'b) bucket;
cmp : ('a -> 'a -> int); (* comparison function *) cmp : ('a -> 'a -> int); (* comparison function *)
@ -93,14 +96,24 @@ let next node n =
(** Find given key in the list, or Not_found *) (** Find given key in the list, or Not_found *)
let find l k = let find l k =
let cmp = l.cmp in let cmp = l.cmp in
let x = ref l.data in let rec search x n =
for i = level l.data - 1 downto 0 do if n < 0 then peek_last x
while lower ~cmp (next !x i) k do x := next !x i done else
done; let x' = next x n in
x := next !x 0; match x' with
match !x with | Nil -> search x (n-1)
| Node (k', v, _) when cmp k k' = 0 -> !v | Node (k', v, _) ->
| _ -> raise Not_found let c = cmp k' k in
if c = 0 then !v
else if c < 0 then search x' n
else search x (n-1)
| Init _ -> assert false
and peek_last x =
match next x 0 with
| Node (k', v, _) when cmp k k' = 0 -> !v
| _ -> raise Not_found
in
search l.data (level l.data - 1)
let mem l k = let mem l k =
try ignore (find l k); true try ignore (find l k); true