Sync

Task/Modular-exponentiation/Haskell/modular-exponentiation.hs

@@ -1,25 +1,12 @@
--- Private type. Do not use outside of the modPow function
-newtype ModN = ModN (Integer, Integer) deriving (Eq, Show)
-instance Num ModN where
-  -- actually only multiplication needs to be implemented
-  -- but we do some of the other ones too for good measure
-  ModN (x, m) + ModN (y, m') | m == m' = ModN ((x + y) `mod` m, m)
-                             | otherwise = undefined
-  ModN (x, m) * ModN (y, m') | m == m' = ModN ((x * y) `mod` m, m)
-                             | otherwise = undefined
-  negate (ModN (x, m)) = ModN ((- x) `mod` m, m)
-  abs _ = undefined
-  signum _ = undefined
-  fromInteger _ = undefined
-
-modPow :: Integer -> Integer -> Integer -> Integer
-modPow _ 0 m = 1 `mod` m
-modPow a b m = c
-  where a' = ModN (a, m)
-        ModN (c, _) = a' ^ b
+powm :: Integer -> Integer -> Integer -> Integer -> Integer
+powm b 0 m r = r
+powm b e m r | e `mod` 2 == 1 = powm (b * b `mod` m) (e `div` 2) m (r * b `mod` m)
+powm b e m r = powm (b * b `mod` m) (e `div` 2) m r
 
 main :: IO ()
-main = print $ modPow a b m
-  where a = 2988348162058574136915891421498819466320163312926952423791023078876139
-        b = 2351399303373464486466122544523690094744975233415544072992656881240319
-        m = 10 ^ 40
+main = putStrLn . show $
+  powm
+    2988348162058574136915891421498819466320163312926952423791023078876139
+    2351399303373464486466122544523690094744975233415544072992656881240319
+    (10 ^ 40)
+    1

Task/Modular-exponentiation/PHP/modular-exponentiation.php

@@ -3,4 +3,3 @@ $a = '2988348162058574136915891421498819466320163312926952423791023078876139';
 $b = '2351399303373464486466122544523690094744975233415544072992656881240319';
 $m = '1' . str_repeat('0', 40);
 echo bcpowmod($a, $b, $m), "\n";
-?>