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structure Hashtable: HASHTABLE = struct
open Array
open Word
(* buf * taken * mask *)
type 'a t = (string * 'a) option array * int * word
val ` = Word.fromInt
val ! = Word.toInt
infixr 4 <<
infix 5 andb
infixr 6 +
infixr 7 *
fun createLog log =
let
val size = `1 << `log
val mask = size - `1
in
(array (Word.toInt size, NONE), 0, mask)
end
exception Full and Exists
fun hash key =
List.foldl (fn (c, s) => s * `31 + `(ord c)) (`17) (explode key)
fun checkFreeSpace (array, taken, _) =
let
open Real
val ` = fromInt
in
if `taken / `(length array) > 0.75 then
raise Full
else
()
end
fun next idx mask = (idx + `1) andb mask
fun lookup2 ((array, _, mask): 'a t) (key: string) f g =
let
fun find idx =
case sub (array, !idx) of
NONE => g ()
| SOME (key', v: 'a) =>
if key' = key then
case f v of
(NONE, res) => res
| (SOME v, res) =>
(update (array, !idx, SOME (key, v)); res)
else
find (next idx mask)
in
find (hash key andb mask)
end
fun lookup H key = lookup2 H key (fn v => (NONE, SOME v)) (fn () => NONE)
fun insert (H as (array, _, mask)) key v =
let
val () = checkFreeSpace H;
fun find idx =
case sub (array, !idx) of
NONE => update (array, !idx, SOME (key, v))
| SOME (key', _) =>
if key' = key then
raise Exists
else
find (next idx mask)
in
find (hash key andb mask)
end
end
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