Adds fast expo in python

Author: pedro823

Math/Fast Exponentiation with Mod/fast_expo_with_mod.py

@@ -0,0 +1,14 @@
+def fast_mult_modulo(a, x, m):
+    ''' returns a^x % m '''
+    ans = 1
+    while x > 0:
+        if x & 1:
+            ans = (ans * a) % m
+        a = (a * a) % m
+        x //= 2
+    return ans
+
+
+if __name__ == '__main__':
+    # testing: should return 445
+    print(fast_mult_modulo(1337, 65537, 2714))