Added powmod in utility and PowerMod in the sintax and semantics of MiniImp

lib/miniImp.ml

@@ -28,6 +28,7 @@ and a_exp =
   | Division of a_exp * a_exp            (* a / a *)
   | Modulo of a_exp * a_exp              (* a % a *)
   | Power of a_exp * a_exp               (* a ^ a *)
+  | PowerMod of a_exp * a_exp * a_exp    (* a ^ a % a *)
   | Rand of a_exp                        (* rand(0, a) *)
 
 
@@ -118,6 +119,12 @@ and evaluate_a (mem: memory) (exp_a: a_exp) =
       let exp_a2val = evaluate_a mem exp_a2 in
       Utility.pow exp_a1val exp_a2val
     )
+  | PowerMod (exp_a1, exp_a2, exp_a3) -> (
+      let exp_a1val = evaluate_a mem exp_a1 in
+      let exp_a2val = evaluate_a mem exp_a2 in
+      let exp_a3val = evaluate_a mem exp_a3 in
+      Utility.powmod exp_a1val exp_a3val exp_a2val
+    )
   | Rand (exp_a) -> (
       Random.int (evaluate_a mem exp_a)
     )

lib/miniImp.mli

@@ -28,6 +28,7 @@ and a_exp =
   | Division of a_exp * a_exp            (* a / a *)
   | Modulo of a_exp * a_exp              (* a % a *)
   | Power of a_exp * a_exp               (* a ^ a *)
+  | PowerMod of a_exp * a_exp * a_exp    (* a ^ a % a *)
   | Rand of a_exp                        (* rand(0, a) *)
 
 

lib/utility.ml

@@ -4,3 +4,10 @@ let rec pow a = function
   | n ->
     let b = pow a (n / 2) in
     b * b * (if n mod 2 = 0 then 1 else a)
+
+let rec powmod a d = function
+  | 0 -> 1
+  | 1 -> a mod d
+  | n ->
+    let b = (powmod a d (n / 2)) mod d in
+    (((b * b) mod d) * (if n mod 2 = 0 then 1 else a)) mod d

lib/utility.mli

@@ -1 +1,3 @@
 val pow : int -> int -> int
+
+val powmod : int -> int -> int -> int