Initial data commit

Task/Modular-exponentiation/Crystal/modular-exponentiation.crystal

@@ -0,0 +1,25 @@
+require "big"
+
+module Integer
+  module Powmod
+
+    # Compute self**e mod m
+    def powmod(e, m)
+      r, b = 1, self.to_big_i
+      while e > 0
+        r = (b * r) % m if e.odd?
+        b = (b * b) % m
+        e >>= 1
+      end
+      r
+    end
+  end
+end
+
+struct Int; include Integer::Powmod end
+
+a = "2988348162058574136915891421498819466320163312926952423791023078876139".to_big_i
+b = "2351399303373464486466122544523690094744975233415544072992656881240319".to_big_i
+m = 10.to_big_i ** 40
+
+puts a.powmod(b, m)