(* This file is free software. See file "license" for more details. *)

type 'a t = 'a -> int

(* 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

(* 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 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[@inline] combine f s x =
  combine2 s (f x)

let combine3 a b 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 =
  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)

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);
  !h

let poly x = Hashtbl.hash x