Java Math issue incorrect output

51^43Mod77 in scientific calculator gives 2 as the output however,

(int)(Math.pow(51,43)%(double)77) gives 12 which should be 2 instead.

Can you please help ?

I guess that the integer overflows resulting in wrong output.

Actually, int isn't the culprit, double is. Double simply isn't big enough to represent 51^43 at integer precision.

Instead, try BigInteger to do the calculation.

It works !!!

However, I do not wish to use modPow

How can i (a raiseto b) Mod c without using modPow?

when a,b and c are BigIntegers

However, I do not wish to use modPow

Why not?

You can write your own method to raise numbers to their powers.

Campbell Ritchie wrote:You can write your own method to raise numbers to their powers.

Does that mean there is no way inbuilt methods trick to achieve this ?

Yes, there is, but you just said that you don't want to use it...

Besides modPow, class BigInteger also has separate pow and mod methods. Lookup the API documentation of class BigInteger.

Oddly enough the pow method takes an int, not a BigInteger like modPow.

Rob Spoor wrote:Oddly enough the pow method takes an int, not a BigInteger like modPow.

Thats the very reason I asked if there isany inbuilt functionality inorder to achieve modPow. If so can someone help me with the code syntax.

Um yes? It's the modPow() method in BigInteger. Why don't you use it?

Or implement pow yourself. It's not that hard. Inefficient maybe, with all the BigInteger objects that are created, but not hard.

Stephan van Hulst wrote:Um yes? It's the modPow() method in BigInteger. Why don't you use it?

I wish to separate the pow and the mod functionalities . Not sure how could I ?

Mohtashim Shaikh wrote:

Stephan van Hulst wrote:Um yes? It's the modPow() method in BigInteger. Why don't you use it?

I wish to separate the pow and the mod functionalities . Not sure how could I ?

1) Write your own pow method
2) Write your own mod method.

OR

1) Use BigInteger's pow method
2) Use BigInteger's mod method