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perf(hash): use FNV hashing

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This commit is contained in:
Simon Cruanes 2021-04-04 17:45:36 -04:00
parent 18fbb950bc
commit 903243643f
1 changed files with 53 additions and 11 deletions
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64
src/util/Hash.ml
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@ -3,24 +3,63 @@
type 'a t = 'a -> int
let bool b = if b then 1 else 2
(* FNV hashing
https://en.wikipedia.org/wiki/Fowler%E2%80%93Noll%E2%80%93Vo_hash_function
*)
let fnv_offset_basis = 0xcbf29ce484222325L
let fnv_prime = 0x100000001b3L
let int i = i land max_int
(* hash an integer *)
let hash_int_ n =
let h = ref fnv_offset_basis in
for k = 0 to 7 do
h := Int64.(mul !h fnv_prime);
h := Int64.(logxor !h (of_int ((n lsr (k * 8)) land 0xff)));
done;
(Int64.to_int !h) land max_int (* truncate back to int and remove sign *)
let string (s:string) = Hashtbl.hash s
let combine2 a b =
let h = ref fnv_offset_basis in
(* we only do one loop, where we mix bytes of [a] and [b], so as
to simplify control flow *)
for k = 0 to 7 do
h := Int64.(mul !h fnv_prime);
h := Int64.(logxor !h (of_int ((a lsr (k * 8)) land 0xff)));
h := Int64.(mul !h fnv_prime);
h := Int64.(logxor !h (of_int ((b lsr (k * 8)) land 0xff)));
done;
Int64.to_int !h land max_int
let combine f a b = Hashtbl.seeded_hash a (f b)
let combine2 a b = Hashtbl.seeded_hash a b
let[@inline] combine f s x =
combine2 s (f x)
let combine3 a b c =
combine2 a b
|> combine2 c
let h = ref fnv_offset_basis in
(* we only do one loop, where we mix bytes of [a] [b] and [c], so as
to simplify control flow *)
for k = 0 to 7 do
h := Int64.(mul !h fnv_prime);
h := Int64.(logxor !h (of_int ((a lsr (k * 8)) land 0xff)));
h := Int64.(mul !h fnv_prime);
h := Int64.(logxor !h (of_int ((b lsr (k * 8)) land 0xff)));
h := Int64.(mul !h fnv_prime);
h := Int64.(logxor !h (of_int ((c lsr (k * 8)) land 0xff)));
done;
Int64.to_int !h land max_int
let combine4 a b c d =
combine2 a b
|> combine2 c
|> combine2 d
let h = ref fnv_offset_basis in
for k = 0 to 7 do
h := Int64.(mul !h fnv_prime);
h := Int64.(logxor !h (of_int ((a lsr (k * 8)) land 0xff)));
h := Int64.(mul !h fnv_prime);
h := Int64.(logxor !h (of_int ((b lsr (k * 8)) land 0xff)));
h := Int64.(mul !h fnv_prime);
h := Int64.(logxor !h (of_int ((c lsr (k * 8)) land 0xff)));
h := Int64.(mul !h fnv_prime);
h := Int64.(logxor !h (of_int ((d lsr (k * 8)) land 0xff)));
done;
Int64.to_int !h land max_int
let pair f g (x,y) = combine2 (f x) (g y)
@ -28,9 +67,12 @@ let opt f = function
| None -> 42
| Some x -> combine2 43 (f x)
let int = hash_int_
let bool b = hash_int_ (if b then 1 else 2)
let list f l = List.fold_left (combine f) 0x42 l
let array f = Array.fold_left (combine f) 0x43
let iarray f = IArray.fold (combine f) 0x44
let string : string t = Hashtbl.hash
let seq f seq =
let h = ref 0x43 in
seq (fun x -> h := combine f !h x);