From 98fd45ab9f7eda1823df3127856eee3dc85dc72e Mon Sep 17 00:00:00 2001
From: Vincent Bernardoff <vb@luminar.eu.org>
Date: Sat, 14 Jan 2017 13:13:19 +0100
Subject: [PATCH] Shell: add `Ring`

---
 src/Makefile       |  2 ++
 src/utils/ring.ml  | 59 ++++++++++++++++++++++++++++++++++++++++++++++
 src/utils/ring.mli | 20 ++++++++++++++++
 3 files changed, 81 insertions(+)
 create mode 100644 src/utils/ring.ml
 create mode 100644 src/utils/ring.mli

diff --git a/src/Makefile b/src/Makefile
index 5f3fa9440..2bbba54b5 100644
--- a/src/Makefile
+++ b/src/Makefile
@@ -163,6 +163,7 @@ UTILS_LIB_INTFS := \
   utils/lwt_pipe.mli \
   utils/IO.mli \
   utils/moving_average.mli \
+  utils/ring.mli \
 
 UTILS_LIB_IMPLS := \
   utils/base48.ml \
@@ -179,6 +180,7 @@ UTILS_LIB_IMPLS := \
   utils/lwt_pipe.ml \
   utils/IO.ml \
   utils/moving_average.ml \
+  utils/ring.ml \
 
 UTILS_PACKAGES := \
   ${MINUTILS_PACKAGES} \
diff --git a/src/utils/ring.ml b/src/utils/ring.ml
new file mode 100644
index 000000000..7c829622e
--- /dev/null
+++ b/src/utils/ring.ml
@@ -0,0 +1,59 @@
+(**************************************************************************)
+(*                                                                        *)
+(*    Copyright (c) 2014 - 2016.                                          *)
+(*    Dynamic Ledger Solutions, Inc. <contact@tezos.com>                  *)
+(*                                                                        *)
+(*    All rights reserved. No warranty, explicit or implicit, provided.   *)
+(*                                                                        *)
+(**************************************************************************)
+
+type 'a raw =
+  | Empty of int
+  | Inited of {
+      data : 'a array ;
+      mutable pos : int ;
+    }
+
+type 'a t = 'a raw ref
+
+let create size = ref (Empty size)
+
+let add r v =
+  match !r with
+  | Empty size ->
+      r := Inited { data = Array.make size v ; pos = 0 }
+  | Inited s ->
+      s.pos <-
+        if s.pos = 2 * Array.length s.data - 1 then
+          Array.length s.data
+        else
+          s.pos + 1 ;
+      s.data.(s.pos mod Array.length s.data) <- v
+
+let add_list r l = List.iter (add r) l
+
+let last r =
+  match !r with
+  | Empty _ -> None
+  | Inited { data ; pos } -> Some data.(pos mod Array.length data)
+
+let fold r ~init ~f =
+  match !r with
+  | Empty _ -> init
+  | Inited { data ; pos } ->
+      let size = Array.length data in
+      let acc = ref init in
+      for i = 0 to min pos (size - 1) do
+        acc := f !acc data.((pos - i) mod size)
+      done ;
+      !acc
+
+let elements t =
+  fold t ~init:[] ~f:(fun acc elt -> elt :: acc)
+
+exception Empty
+
+let last_exn r =
+  match last r with
+  | None -> raise Empty
+  | Some d -> d
diff --git a/src/utils/ring.mli b/src/utils/ring.mli
new file mode 100644
index 000000000..fe1b71b51
--- /dev/null
+++ b/src/utils/ring.mli
@@ -0,0 +1,20 @@
+(**************************************************************************)
+(*                                                                        *)
+(*    Copyright (c) 2014 - 2016.                                          *)
+(*    Dynamic Ledger Solutions, Inc. <contact@tezos.com>                  *)
+(*                                                                        *)
+(*    All rights reserved. No warranty, explicit or implicit, provided.   *)
+(*                                                                        *)
+(**************************************************************************)
+
+(** Imperative Ring Buffer *)
+
+type 'a t
+val create : int -> 'a t
+val add : 'a t -> 'a -> unit
+val add_list : 'a t -> 'a list -> unit
+val last : 'a t -> 'a option
+exception Empty
+val last_exn : 'a t -> 'a
+val fold : 'a t -> init:'b -> f:('b -> 'a -> 'b) -> 'b
+val elements : 'a t -> 'a list