Merge with cfg

lib/utility/utility.ml

@@ -0,0 +1,25 @@
+let rec pow a = function
+  | 0 -> 1
+  | 1 -> a
+  | 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
+
+
+let alphabet = "abcdefghijklmnopqrstuvwxyz"
+let base = 26
+
+let rec fromIntToString (x: int) : string =
+  if x < 0 then
+    ""
+  else if x < base then
+    String.get alphabet x |> String.make 1
+  else
+    (fromIntToString (x/base - 1)) ^ (String.get alphabet (x mod base) |> String.make 1)