mirror of
https://github.com/c-cube/ocaml-containers.git
synced 2026-05-06 01:14:33 -04:00
82 lines
2.5 KiB
OCaml
82 lines
2.5 KiB
OCaml
open CCHash
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module T = (val Containers_testlib.make ~__FILE__ ())
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include T;;
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t @@ fun () -> int 42 >= 0;;
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t @@ fun () -> int max_int >= 0;;
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t @@ fun () -> int max_int = int max_int;;
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t @@ fun () -> int min_int >= 0;;
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t @@ fun () -> int 0 >= 0;;
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t @@ fun () -> char 'c' >= 0;;
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t @@ fun () -> int 152352 = int 152352;;
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t @@ fun () -> list_comm int [ 1; 2 ] = list_comm int [ 2; 1 ];;
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t @@ fun () -> list_comm int [ 1; 2 ] <> list_comm int [ 2; 3 ];;
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t @@ fun () -> string "abcd" >= 0;;
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t @@ fun () -> string "abc" <> string "abcd";;
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q Q.int (fun i ->
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Q.assume (i >= 0);
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int i = int64 (Int64.of_int i))
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;;
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(* --- stress tests -------------------------------------------------------- *)
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(* Chi-squared distribution test over [count] consecutive integers in [buckets] buckets.
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A uniform hash gives chi2 ~ buckets-1; we allow 4 standard deviations of slack. *)
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t ~name:"int hash distribution chi2" @@ fun () ->
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let count = 50_000 and buckets = 500 in
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let counts = Array.make buckets 0 in
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for i = 0 to count - 1 do
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let b = CCHash.int i mod buckets in
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counts.(b) <- counts.(b) + 1
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done;
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let expected = float count /. float buckets in
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let c2 =
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Array.fold_left
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(fun acc c -> acc +. (((float c -. expected) ** 2.0) /. expected))
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0.0 counts
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in
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let df = float (buckets - 1) in
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c2 < df +. (4.0 *. sqrt (2.0 *. df))
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;;
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(* Strict avalanche criterion: flip one input bit, expect ~50% output bits to change. *)
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t ~name:"int hash avalanche" @@ fun () ->
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let bits = Sys.int_size - 1 in
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let total_flips = ref 0 in
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let total = ref 0 in
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let rng = Random.State.make [| 42; 17; 99 |] in
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for _ = 1 to 300 do
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let x = Random.State.bits rng in
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let hx = CCHash.int x in
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for b = 0 to bits - 1 do
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let hx' = CCHash.int (x lxor (1 lsl b)) in
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total_flips := !total_flips + CCInt.popcount (hx lxor hx');
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total := !total + bits
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done
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done;
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let frac = float !total_flips /. float !total in
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frac >= 0.45 && frac <= 0.55
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;;
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(* String hash: no collisions among distinct keys. *)
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t ~name:"string hash no collisions" @@ fun () ->
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let n = 50_000 in
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let tbl = Hashtbl.create n in
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let ok = ref true in
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for i = 0 to n - 1 do
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let h = CCHash.string (Printf.sprintf "key:%d" i) in
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if Hashtbl.mem tbl h then ok := false;
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Hashtbl.replace tbl h ()
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done;
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!ok
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;;
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(* CCHash64 pipeline matches CCHash.pair combiner. *)
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q Q.int (fun i ->
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let j = i lxor 0xdeadbeef in
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let h_pair = CCHash.pair CCHash.int CCHash.int (i, j) in
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let h_manual =
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CCHash64.(finalize (int (int seed (CCHash.int i)) (CCHash.int j)))
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in
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h_pair = h_manual)
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