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hash-table.sml
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hash-table.sml
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functor HashTable (structure Key : HASHABLE)
:> HASH_TABLE where type key = Key.t
=
struct
type init = int
type key = Key.t
datatype 'a entry =
Nil
| Cons of word * key * 'a * 'a entry ref
datatype 'a bucket =
Zero
| One of key * 'a
| Many of 'a entry ref (* invariant: length >=2 *)
type 'a table =
{ residents : int ref, (* current number of residents *)
size : word,
thresh : int, (* number of residents at which to resize *)
arr : 'a bucket array } ref
exception Absent
fun resizeLoad n = n div 4 * 3
fun initial sz =
if sz <= 0 then
raise (Fail "illegal size")
else
{ residents = ref 0,
size = Word.fromInt sz,
thresh = resizeLoad sz,
arr = Array.array (sz, Zero) }
fun table sz = ref (initial sz)
fun reset table sz =
table := initial sz
fun size (ref { residents, ... } : 'a table) = !residents
fun findEntry lr hash key =
(case !lr of
Nil =>
lr
| Cons (hash', key', _, rest) =>
if hash = hash' andalso Key.eq (key, key') then
lr
else
findEntry rest hash key)
fun resize (table as ref { residents, size, thresh, arr, ... } : 'a table) =
if !residents < thresh then
()
else
let
val newsize = 2 * Word.toInt size
val newsize' = Word.fromInt newsize
val arr' = Array.array (newsize, Zero)
fun moveInto hash key datum =
let
val n = Word.toInt (hash mod newsize')
in
(case Array.sub (arr', n) of
Zero =>
Array.update (arr', n, One (key, datum))
| One (key', datum') =>
Array.update (arr', n,
Many (ref (Cons (hash, key, datum,
ref (Cons (Key.hash key', key', datum',
ref Nil))))))
| Many lr =>
Array.update (arr', n, Many (ref (Cons (hash, key, datum, lr)))))
end
fun moveList lr =
(case !lr of
Nil => ()
| Cons (hash, key, datum, rest) =>
(
moveInto hash key datum;
moveList rest
))
fun move bucket =
(case bucket of
Zero => ()
| One (key, datum) =>
moveInto (Key.hash key) key datum
| Many lr =>
moveList lr)
in
(* Move entries to new array. *)
Array.app move arr;
table := { residents = residents,
size = newsize',
thresh = resizeLoad newsize,
arr = arr' }
end
fun member (ref { size, arr, ... } : 'a table) key =
let
val hash = Key.hash key
val n = Word.toInt (hash mod size)
in
(case Array.sub (arr, n) of
Zero => false
| One (key', _) =>
Key.eq (key, key')
| Many lr =>
(case !(findEntry lr hash key) of
Nil => false
| Cons _ => true))
end
fun insert (table as ref { residents, size, arr, ... } : 'a table) key datum =
let
val hash = Key.hash key
val n = Word.toInt (hash mod size)
in
(case Array.sub (arr, n) of
Zero =>
(
Array.update (arr, n,
One (key, datum));
residents := !residents + 1;
resize table
)
| One (key', datum') =>
if Key.eq (key, key') then
Array.update (arr, n, One (key, datum))
else
(
Array.update (arr, n,
Many (ref (Cons (hash, key, datum,
ref (Cons (Key.hash key', key', datum',
ref Nil))))));
residents := !residents + 1;
resize table
)
| Many lr =>
(case findEntry lr hash key of
ref Nil =>
(
Array.update (arr, n,
Many (ref (Cons (hash, key, datum, lr))));
residents := !residents + 1;
resize table
)
| lr' as ref (Cons (_, _, _, rest)) =>
lr' := Cons (hash, key, datum, rest)))
end
fun remove (table as ref { residents, size, arr, ... } : 'a table) key =
let
val hash = Key.hash key
val n = Word.toInt (hash mod size)
in
(case Array.sub (arr, n) of
Zero => ()
| One (key', _) =>
if Key.eq (key, key') then
(
Array.update (arr, n, Zero);
residents := !residents - 1
)
else
()
| Many lr =>
(case findEntry lr hash key of
ref Nil => ()
| lr' as ref (Cons (_, _, _, rest)) =>
(
lr' := !rest;
(case !lr of
Cons (_, key', datum', ref Nil) =>
Array.update (arr, n, One (key', datum'))
| Nil =>
raise (Fail "invariant")
| _ => ());
residents := !residents - 1
)))
end
fun lookup (table as ref { size, arr, ... } : 'a table) key =
let
val hash = Key.hash key
val n = Word.toInt (hash mod size)
in
(case Array.sub (arr, n) of
Zero =>
raise Absent
| One (key', datum) =>
if Key.eq (key, key') then
datum
else
raise Absent
| Many lr =>
(case findEntry lr hash key of
ref Nil =>
raise Absent
| ref (Cons (_, _, datum, _)) =>
datum))
end
fun find table key =
(SOME (lookup table key)
handle Absent => NONE)
fun operate' (table as ref { residents, size, arr, ... } : 'a table) key absentf presentf =
let
val hash = Key.hash key
val n = Word.toInt (hash mod size)
in
(case Array.sub (arr, n) of
Zero =>
let
val datumo = absentf ()
in
(case datumo of
NONE => ()
| SOME datum =>
(
Array.update (arr, n, One (key, datum));
residents := !residents + 1;
resize table
));
(NONE, datumo)
end
| One (key', datum') =>
if Key.eq (key, key') then
let
val datumo = presentf datum'
in
(case datumo of
NONE =>
(
Array.update (arr, n, Zero);
residents := !residents - 1
)
| SOME datum =>
Array.update (arr, n, One (key, datum)));
(SOME datum', datumo)
end
else
let
val datumo = absentf ()
in
(case datumo of
NONE =>
()
| SOME datum =>
(
Array.update (arr, n,
Many (ref (Cons (hash, key, datum,
ref (Cons (Key.hash key', key', datum',
ref Nil))))));
residents := !residents + 1;
resize table
));
(NONE, datumo)
end
| Many lr =>
(case findEntry lr hash key of
ref Nil =>
let
val datumo = absentf ()
in
(case datumo of
NONE => ()
| SOME datum =>
(
Array.update (arr, n,
Many (ref (Cons (hash, key, datum, lr))));
residents := !residents + 1;
resize table
));
(NONE, datumo)
end
| lr' as ref (Cons (_, _, datum', rest)) =>
let
val datumo = presentf datum'
in
(case datumo of
NONE =>
(
lr' := !rest;
(case !lr of
Cons (_, key'', datum'', ref Nil) =>
Array.update (arr, n, One (key'', datum''))
| Nil =>
raise (Fail "invariant")
| _ => ());
residents := !residents - 1
)
| SOME datum =>
lr' := Cons (hash, key, datum, rest));
(SOME datum', datumo)
end))
end
fun operate table key absentf presentf =
let
val (x, y) = operate' table key (SOME o absentf) (SOME o presentf)
in
(x, valOf y)
end
fun insertMerge table key x f =
(
operate' table key (fn () => SOME x) (SOME o f);
()
)
fun lookupOrInsert table key datumf =
let
val (x, y) = operate' table key (SOME o datumf) (fn x => SOME x)
in
valOf y
end
fun lookupOrInsert' table key datumf =
let
val (x, y) = operate' table key (SOME o datumf) (fn x => SOME x)
in
(valOf y, isSome x)
end
fun foldEntry f x entry =
(case entry of
Nil => x
| Cons (_, key, datum, ref next) =>
foldEntry f (f (key, datum, x)) next)
fun fold f x (ref { arr, ... } : 'a table) =
Array.foldl
(fn (Zero, acc) => acc
| (One (key, datum), acc) => f (key, datum, acc)
| (Many (ref l), acc) => foldEntry f acc l)
x
arr
fun toList table =
fold (fn (key, datum, l) => (key, datum) :: l) [] table
fun appEntry f entry =
(case entry of
Nil => ()
| Cons (_, key, datum, ref next) =>
(
f (key, datum);
appEntry f next
))
fun app f (ref { arr, ... } : 'a table) =
Array.app
(fn Zero => ()
| One (key, datum) => f (key, datum)
| Many (ref l) => appEntry f l)
arr
end