How to avoid java.lang.OutOfMemoryError?

Question

I have two simple java codes.The first one defines constant power as power = a.pow(b);

import java.math.BigInteger;    
public class FermatOne    
{    
    publ         


        

Answer 1

It's just a guess, but BigInteger.ONE.shiftLeft(332192810); will internally create an int array of length x + 10381025. Since an int is 4 bytes big you'll get about 40 mega bytes of data just for that one call. I assume the other calls copy that data around and thus you get that high a memory consumption.

Answer 2

You're trying to calculate a number like 2 ^ (15 * 2 ^ 332192809). I don't know if you could even fit such a number in the universe!! Or maybe, the answer is simply... 42 ? ;-)

On a more serious note, you'll really have trouble, calculating this number. Encoded in bits, 15 * 2 ^ 332192810 would require almost a gigabyte by itself. Then raising 2 to that power again, I don't want to know...

On a more serious note, when you dig into the implementation of java.math.BigInteger, I think that you just run into such an error faster with the left shift, as that is implemented much more efficiently, than the power method. Having said this, have you tried to force garbage collection in your code, using System.gc()?

UPDATE: My original reasoning might've been wrong. 2 ^ 332192809 can be calculated with 1GB. And the overall result might be "modded" efficiently by java.math.BigInteger, although I believe that this calculation might take a while...