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88 lines
2.9 KiB
OCaml
88 lines
2.9 KiB
OCaml
(*
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Copyright (c) 2013, Simon Cruanes
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All rights reserved.
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Redistribution and use in source and binary forms, with or without
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modification, are permitted provided that the following conditions are met:
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Redistributions of source code must retain the above copyright notice, this
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list of conditions and the following disclaimer. Redistributions in binary
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form must reproduce the above copyright notice, this list of conditions and the
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following disclaimer in the documentation and/or other materials provided with
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the distribution.
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THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS "AS IS" AND
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ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED
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WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE
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DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT HOLDER OR CONTRIBUTORS BE LIABLE
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FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
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DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR
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SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER
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CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY,
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OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE
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OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
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*)
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(** an imperative cache for memoization of pairs *)
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module type S =
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sig
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type key
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type 'a t
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(** create a cache with given size *)
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val create : int -> (key -> key -> 'a) -> 'a t
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(** find a value in the cache *)
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val lookup : 'a t -> key -> key -> 'a
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(** clear the cache from its content *)
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val clear : 'a t -> unit
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end
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module type CachedType =
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sig
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type t
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val hash : t -> int
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val equal : t -> t -> bool
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end
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module Make(HType : CachedType) =
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struct
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type key = HType.t
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(** A slot of the array contains a (key, value, true)
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if key->value is stored there (at index hash(key) % length),
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(null, null, false) otherwise.
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The first slot in the array contains the function
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used to produce the value upon a cache miss. *)
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type 'a t = (key * key * 'a * bool) array
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let my_null = (Obj.magic None, Obj.magic None, Obj.magic None, false)
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let set_fun c f = c.(0) <- Obj.magic f
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let create size f =
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let c = Array.create (size+1) my_null in
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c.(0) <- Obj.magic f;
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c
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let lookup c k1 k2 =
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let i = (((HType.hash k1 + 17) lxor HType.hash k2) mod (Array.length c -1)) + 1 in
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match c.(i) with
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| (_, _, _, false) ->
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let v = ((Obj.magic c.(0)) : key -> key -> 'a) k1 k2 in
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c.(i) <- (k1, k2, v, true); v
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| (k1', k2', _, true) when not (HType.equal k1 k1') || not (HType.equal k2 k2')->
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let v = ((Obj.magic c.(0)) : key -> key -> 'a) k1 k2 in
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c.(i) <- (k1, k2, v, true); v
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| (_, _, v, true) -> v
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let clear c =
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let f = c.(0) in
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Array.iteri (fun i _ -> c.(i) <- my_null) c;
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c.(0) <- f
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end
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