1 files changed, 17 insertions, 0 deletions
diff --git a/clib/cArray.ml b/clib/cArray.ml
index e0a1859184..145a32cf45 100644
--- a/clib/cArray.ml
+++ b/clib/cArray.ml
@@ -52,6 +52,8 @@ sig
   val map2_i : (int -> 'a -> 'b -> 'c) -> 'a array -> 'b array -> 'c array
   val map3 :
     ('a -> 'b -> 'c -> 'd) -> 'a array -> 'b array -> 'c array -> 'd array
+  val map3_i :
+    (int -> 'a -> 'b -> 'c -> 'd) -> 'a array -> 'b array -> 'c array -> 'd array
   val map_left : ('a -> 'b) -> 'a array -> 'b array
   val iter2_i : (int -> 'a -> 'b -> unit) -> 'a array -> 'b array -> unit
   val fold_left_map : ('a -> 'b -> 'a * 'c) -> 'a -> 'b array -> 'a * 'c array
@@ -358,6 +360,21 @@ let map3 f v1 v2 v3 =
     res
   end
 
+let map3_i f v1 v2 v3 =
+  let len1 = Array.length v1 in
+  let len2 = Array.length v2 in
+  let len3 = Array.length v3 in
+  let () = if not (Int.equal len1 len2 && Int.equal len1 len3) then invalid_arg "Array.map3_i" in
+  if Int.equal len1 0 then
+    [| |]
+  else begin
+    let res = Array.make len1 (f 0 (uget v1 0) (uget v2 0) (uget v3 0)) in
+    for i = 1 to pred len1 do
+      Array.unsafe_set res i (f i (uget v1 i) (uget v2 i) (uget v3 i))
+    done;
+    res
+  end
+
 let map_left f a = (* Ocaml does not guarantee Array.map is LR *)
   let l = Array.length a in (* (even if so), then we rewrite it *)
   if Int.equal l 0 then [||] else begin