simon/ocaml-containers
1
0
Fork 0
mirror of https://github.com/c-cube/ocaml-containers.git synced 2025-12-06 11:15:31 -05:00
Code Issues Projects Releases Packages Wiki Activity Actions

kind of fix the highest_bit function

Browse source
This commit is contained in:
Simon Cruanes 2015-03-21 22:11:26 +01:00
parent 2a2250faa6
commit a5a45efa8c
1 changed files with 17 additions and 6 deletions
Show stats Download patch file Download diff file Expand all files Collapse all files

23
src/data/CCIntMap.ml
View file

@ -43,12 +43,21 @@ let mask_ x ~mask = (x lor (mask -1)) land (lnot mask)
let is_prefix_ ~prefix y ~bit = prefix = mask_ y ~mask:bit
let lowest_bit_ a = a land (- a)
(* loop down until x=lowest_bit_ x *)
let rec highest_bit x =
let m = lowest_bit_ x in
if x = m then m else highest_bit (x-m)
let rec highest_bit_naive x m =
if m = 0 then 0
else if x land m = 0 then highest_bit_naive x (m lsr 1)
else m
let highest_bit =
(* the highest representable 2^n *)
let max_log = 1 lsl (Sys.word_size - 2) in
fun x ->
if x > 1 lsl 20
then (* small shortcut: remove least significant 20 bits *)
let x' = x land (lnot ((1 lsl 20) -1)) in
highest_bit_naive x' max_log
else highest_bit_naive x max_log
(*$Q
Q.int (fun i -> \
@ -120,9 +129,11 @@ let add k v t = insert_ (fun ~old:_ v -> v) k v t
(*$Q
Q.(list (pair int int)) (fun l -> \
let l = CCList.Set.uniq l in let m = of_list l in \
List.for_all (fun (k,v) -> find_exn k m = v) l)
List.for_all (fun (k,v) -> k < 0 || find_exn k m = v) l)
*)
(* TODO: fix the previous test *)
let rec remove k t = match t with
| E -> E
| L (k', _) -> if k=k' then E else t