How to compute pow(x, y) % n

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Hello everyone!

I have to compute the value of expression: pow(x, y) % n (remainder of pow(x,y) divided by n)
I've tried like this:

Java

long L1 = ((long)Math.pow(123,17)) % 3233;
long L2 = ((long)Math.pow(L1,2753)) % 3233;
System.out.format("L1 = %d%n", L1);
System.out.format("L2 = %d%n", L2);

and I haven't got what I've expected.
I think the problem is that we're dealing with too big numbers.

How can I compute these thing?

Thanks in advance!

Posted 2-May-12 21:15pm

svatstika

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CPallini · Accepted Answer · 2012-05-02T21:54:00

Solution 1

Use the BigInteger[^] class.
For instance:

Java

// implementation of 'long L1 = ((long)Math.pow(123,17)) % 3233;'
BigInteger b = new BigInteger("123");
BigInteger e = new BigInteger("17");
BigInteger m = new BigInteger("3233");
BigInteger r;
r = b.modPow(e, m);

Posted 2-May-12 21:54pm

CPallini