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(* using the hash_variant of pa_type_conv at compile time *)
let repr_of_poly_variant : [> ] -> int = fun variant ->
let obj = Obj.repr variant in
if Obj.is_int obj then Obj.obj obj
else
let size = Obj.size obj in
assert (size = 2);
let repr = Obj.field obj 0 in
(assert (Obj.is_int repr));
Obj.obj repr
let hash_variant s =
let accu = ref 0 in
for i = 0 to String.length s - 1 do
accu := 223 * !accu + Char.code s.[i]
done;
(* reduce to 31 bits *)
accu := !accu land (1 lsl 31 - 1);
(* make it signed for 64 bits architectures *)
if !accu > 0x3FFFFFFF then !accu - (1 lsl 31) else !accu
(* a few unit tests of cases that have triggered diffs in the past of this
lib *)
let () = assert (repr_of_poly_variant `Latency_stats = hash_variant "Latency_stats")
let () = assert (repr_of_poly_variant `zero = hash_variant "zero")
let double_array_value = Obj.magic 0.
let has_double_array_tag a = Pervasives.(=) Obj.double_array_tag (Obj.tag (Obj.repr a))
let () =
let module M = struct
type double = { a : float ; b : float }
type simple = { c : float ; d : int }
let double = { a = double_array_value; b = double_array_value; }
let simple = { c = double_array_value; d = double_array_value; }
end in
assert (has_double_array_tag M.double);
assert (not (has_double_array_tag M.simple));
;;
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