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kind of fix the highest_bit function

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Simon Cruanes 2015-03-21 22:11:26 +01:00
parent 2a2250faa6
commit a5a45efa8c
1 changed files with 17 additions and 6 deletions
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23
src/data/CCIntMap.ml
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@ -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 is_prefix_ ~prefix y ~bit = prefix = mask_ y ~mask:bit
let lowest_bit_ a = a land (- a)
(* loop down until x=lowest_bit_ x *) (* loop down until x=lowest_bit_ x *)
let rec highest_bit x = let rec highest_bit_naive x m =
let m = lowest_bit_ x in if m = 0 then 0
if x = m then m else highest_bit (x-m) 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
Q.int (fun i -> \ Q.int (fun i -> \
@ -120,9 +129,11 @@ let add k v t = insert_ (fun ~old:_ v -> v) k v t
(*$Q (*$Q
Q.(list (pair int int)) (fun l -> \ Q.(list (pair int int)) (fun l -> \
let l = CCList.Set.uniq l in let m = of_list l in \ 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 let rec remove k t = match t with
| E -> E | E -> E
| L (k', _) -> if k=k' then E else t | L (k', _) -> if k=k' then E else t