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improve test hash

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This commit is contained in:
Simon Cruanes 2021-04-05 00:13:33 -04:00
parent 8d6c7470eb
commit 45b3956421
2 changed files with 19 additions and 54 deletions
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2
src/core/tests/dune
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@ -10,7 +10,7 @@
(name test_hash)
(modules test_hash)
(flags :standard -warn-error -a+8)
(libraries containers))
(libraries containers iter))
(executable
(name test_random)

71
src/core/tests/test_hash.ml
View file

@ -13,6 +13,9 @@ module Hist = struct
let add self x =
Hashtbl.replace self.tbl x (1 + try Hashtbl.find self.tbl x with _ ->0);
self.n_samples <- 1 + self.n_samples
let add_n self x n =
Hashtbl.replace self.tbl x (n + try Hashtbl.find self.tbl x with _ ->0);
self.n_samples <- n + self.n_samples
let pp out (self:t) : unit =
let max = Hashtbl.fold (fun k _ n -> max k n) self.tbl 0 in
@ -24,69 +27,31 @@ module Hist = struct
done
end
(* how long does it take to get back to [n0]?
@param max if provided, stop when reaching it *)
let orbit_size ?(max=max_int) n0 : int =
let size = ref 1 in
let n = ref (H.int n0) in
while !n <> n0 && !size < max do
n := H.int !n;
incr size;
done;
!size
let reset_line = "\x1b[2K\r"
let t_int n1 n2 =
Printf.printf "test hash_int on %d--%d\n" n1 n2;
let hist = Hist.create() in
let count = Hashtbl.create 128 in
for i=n1 to n2 do
Printf.printf "%sorbit for %d…%!" reset_line i;
let orb = orbit_size ~max:30_000 i in
Hist.add hist orb;
Printf.printf "%shash %d…%!" reset_line i;
let h = H.int i in
Hashtbl.replace count h (1 + CCHashtbl.get_or count h ~default:0);
if i mod 1024*1024*1024 = 0 then Gc.major();
done;
Printf.printf "%s%!" reset_line;
(* reverse table *)
let by_count =
CCHashtbl.to_iter count
|> Iter.map (fun (_h,n) -> n)
|> Iter.count ~hash:H.int
in
let hist = Hist.create() in
by_count (fun (n,i) -> Hist.add_n hist n i);
Format.printf "histogram:@.%a@." Hist.pp hist;
(*assert (Hist.check_uniform hist);*)
()
(* how long does it take to get back to [n0] by
hashing [n] with [m0] ?
@param max if provided, stop when reaching it *)
let left_orbit_size ?(max=max_int) n0 m0 : int =
let size = ref 1 in
let n = ref (H.combine2 (H.int n0) (H.int m0)) in
while !n <> n0 && !size < max do
n := H.combine2 (H.int !n) (H.int m0);
incr size;
done;
!size
let t_int2 n1 n2 n3 n4 =
Printf.printf "test hash combine2 on %d--%d x %d--%d\n" n1 n2 n3 n4;
let hist = Hist.create() in
for i=n1 to n2 do
for j=n3 to n4 do
Printf.printf "%sleft-orbit for %d x %d…%!" reset_line i j;
let orb = left_orbit_size ~max:20_000 i j in
Hist.add hist orb;
done;
done;
Printf.printf "%s%!" reset_line;
Format.printf "histogram:@.%a@." Hist.pp hist;
()
let help =
{|Test the hash function on integers, by computing orbits for inputs.
An orbit is a cycle [n -> h(n) -> h(h(n)) -> h^3(n) -> … h^k(n)]
where [h^k(n) == n]. For a good hash functions, orbits should be as long as
possible.
|}
let () =
print_endline help;
t_int 0 80_000;
t_int 3_000_000 3_040_000;
t_int (-40_000) (-17_000);
t_int2 10 300 600 800;
t_int 0 2_000_000;
t_int (-4_000_000) (-3_500_000);
()