unikernel/duniverse/base/test/test_clz_ctz.ml

@@ -0,0 +1,112 @@
+open! Import
+
+module E = struct
+  type t =
+    { clz : int
+    ; ctz : int
+    }
+  [@@deriving compare, sexp_of]
+end
+
+module type T = sig
+  type t [@@deriving sexp_of]
+
+  val one : t
+  val ( lsl ) : t -> int -> t
+  val clz : t -> int
+  val ctz : t -> int
+  val num_bits : int
+end
+
+module Make (Int : T) = struct
+  let%expect_test "one-hot" =
+    let clz_and_ctz int = { E.clz = Int.clz int; ctz = Int.ctz int } in
+    for i = 0 to Int.num_bits - 1 do
+      [%test_result: E.t]
+        ~expect:{ E.clz = Int.num_bits - 1 - i; ctz = i }
+        (clz_and_ctz Int.(one lsl i))
+    done
+  ;;
+end
+
+include Make (Nativeint)
+include Make (Int63)
+include Make (Int63.Private.Emul)
+
+include Make (struct
+  include Int
+
+  let%expect_test "zero" =
+    (* [clz 0] is guaranteed to be num_bits for int. We compute clz on the tagged
+         representation of int's, and the binary representation of the int [0] is
+         num_bits 0's followed by a 1 (the tag bit). *)
+    [%test_result: int] ~expect:num_bits (clz 0)
+  ;;
+
+  (* [ctz 0] is unspecified. On linux it seems to be stable and equal to the system
+       word size (which is num_bits + 1).
+       ran 2019-02-11 on linux:
+       {v
+        [%test_result: int] ~expect:(num_bits + 1) (ctz 0)
+       v}
+
+       in javascript, it is 32 (which is num_bits):
+       ran 2019-02-11 on javascript:
+       {v
+        [%test_result: int] ~expect:(num_bits) (ctz 0)
+       v}
+    *)
+end)
+
+include Make (struct
+  include Int32
+
+  let clz_and_ctz i32 = { E.clz = clz i32; ctz = ctz i32 }
+
+  let%expect_test "extra examples" =
+    [%test_result: E.t] ~expect:{ clz = 31; ctz = 0 } (clz_and_ctz 0b1l);
+    [%test_result: E.t] ~expect:{ clz = 30; ctz = 1 } (clz_and_ctz 0b10l);
+    [%test_result: E.t] ~expect:{ clz = 30; ctz = 0 } (clz_and_ctz 0b11l);
+    [%test_result: E.t] ~expect:{ clz = 25; ctz = 1 } (clz_and_ctz 0b1000010l);
+    [%test_result: E.t]
+      ~expect:{ clz = 8; ctz = 6 }
+      (clz_and_ctz 0b100000010000001001000000l);
+    [%test_result: E.t]
+      ~expect:{ clz = 0; ctz = 31 }
+      (clz_and_ctz 0b10000000000000000000000000000000l);
+    [%test_result: E.t]
+      ~expect:{ clz = 9; ctz = 6 }
+      (clz_and_ctz 0b00000000010000000100000001000000l);
+    [%test_result: E.t]
+      ~expect:{ clz = 0; ctz = 6 }
+      (clz_and_ctz 0b10000000010000000100000001000000l)
+  ;;
+end)
+
+include Make (struct
+  include Int64
+
+  let clz_and_ctz i64 = { E.clz = clz i64; ctz = ctz i64 }
+
+  let%expect_test "extra examples" =
+    [%test_result: E.t] ~expect:{ clz = 63; ctz = 0 } (clz_and_ctz 0b1L);
+    [%test_result: E.t] ~expect:{ clz = 62; ctz = 1 } (clz_and_ctz 0b10L);
+    [%test_result: E.t] ~expect:{ clz = 62; ctz = 0 } (clz_and_ctz 0b11L);
+    [%test_result: E.t] ~expect:{ clz = 57; ctz = 1 } (clz_and_ctz 0b1000010L);
+    [%test_result: E.t]
+      ~expect:{ clz = 40; ctz = 6 }
+      (clz_and_ctz 0b100000010000001001000000L);
+    [%test_result: E.t]
+      ~expect:{ clz = 0; ctz = 63 }
+      (clz_and_ctz 0b1000000000000000000000000000000000000000000000000000000000000000L);
+    [%test_result: E.t]
+      ~expect:{ clz = 32; ctz = 31 }
+      (clz_and_ctz 0b0000000000000000000000000000000010000000000000000000000000000000L);
+    [%test_result: E.t]
+      ~expect:{ clz = 32; ctz = 6 }
+      (clz_and_ctz 0b0000000000000000000000000000000010000000010000000100000001000000L);
+    [%test_result: E.t]
+      ~expect:{ clz = 33; ctz = 6 }
+      (clz_and_ctz 0b0000000000000000000000000000000001000000010000000100000001000000L)
+  ;;
+end)