CODEWITHSUNDEEP
javabit-manipulationbiginteger
Mani Sankar
Mani Sankar

Reputation: 821

Shifting BigInteger of Java by long variable

I know there are methods shiftLeft(int n) and shiftRight(int n) for BigInteger class which only takes int type as an argument but I have to shift it by a long variable. Is there any method to do it?

Upvotes: 4

Views: 449

Answers (3)

Peter Lawrey
Peter Lawrey

Reputation: 533500

BigInteger can only have Integer.MAX_VALUE bits. Shifting right by more than this will always be zero. Shift left any value but zero will be an overflow.

From the Javadoc

 * BigInteger constructors and operations throw {@code ArithmeticException} when
 * the result is out of the supported range of
 * -2<sup>{@code Integer.MAX_VALUE}</sup> (exclusive) to
 * +2<sup>{@code Integer.MAX_VALUE}</sup> (exclusive).

If you need more than 2 billion bits to represent your value, you have a fairly usual problem, BigInteger wasn't designed for.

If you need to do bit manipulation on a very large scale, I suggest having an BitSet[] This will allow up to 2 bn of 2 bn bit sets, more than your addressable memory.

yes the long variable might go up to 10^10

For each 10^10 bit number you need 1.25 TB of memory. For this size of data, you may need to store it off heap, we have a library which persist this much data in a single memory mapping without using much heap, but you need to have this much space free on a single disk at least. https://github.com/OpenHFT/Chronicle-Bytes

Upvotes: 6

Andreas
Andreas

Reputation: 159086

Since 2 ^ X is equal to 10 ^ (X * ln(2) / ln(10)), we can calculate for X = 10 ^ 10:

2 ^ (10 ^ 10) = 10 ^ 3,010,299,956.63981195...
              = 10 ^ 3,010,299,956 * 10 ^ 0.63981195...
              = 4.3632686... * 10 ^ 3,010,299,956

Meaning 4 followed by more than 3 billion more digits.

That's a very large number and will take some doing storing that to full precision.

Upvotes: 0

Paul Boddington
Paul Boddington

Reputation: 37645

BigInteger does not support values where long shift amounts would be appropriate. I tried

BigInteger a = BigInteger.valueOf(2).pow(Integer.MAX_VALUE);

and I got the following exception:

Exception in thread "main" java.lang.ArithmeticException: BigInteger would overflow supported range.

Upvotes: 4

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