Java BigInteger pow with BigInteger exponent

Question

Hi i want to calculate

2^(256bit number)

in java, but biginteger's pow function just can handle ints.

How can i calculate with larger numbers?

Is there any library?

i want to calculate all numbers from

2^0
2^1
2^2
...
2^(10^77)

You can always use more pows... (if not for the bit shift). Curious however: Why? — ppeterka
– ppeterka, Commented Sep 8, 2013 at 20:19
possible duplicate of Very Large Numbers in Java Without using java.math.BigInteger — leonm
– leonm, Commented Sep 8, 2013 at 20:20
For this particular case you can use shiftLeft, but it is a weird oversight. — Antimony
– Antimony, Commented Sep 8, 2013 at 20:20
Just write a 1 and put number times 0 to get the binary representation, it can't be hard to get this into whatever other form you need? — mvds
– mvds, Commented Sep 8, 2013 at 20:20

Antimony · Accepted Answer · 2013-09-08 20:24:21Z

4

I suspect the reason they didn't bother including anything like this is that in most cases, the number would be too big to represent.

Consider 2^(256 bit number). The result has (256bit number) bits, meaning that it takes more memory then there are particles in the universe.

So you'll have to find a different way to represent your logic. Perhaps you could do it symbolically.

It would be possible to do 2^(2^32) and exponents close to that, but this was probably seen as a niche case that they just didn't bother adding a function for.

answered Sep 8, 2013 at 20:24

Antimony

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11 Comments

ppeterka Over a year ago

I've been wondering also... According to this: "The number of atoms in the entire observable universe is estimated to be within the range of 10^78 to 10^82."

Antimony Over a year ago

2^256 just happens to be 10^77, so I was actually closer then I thought. Anyway, it's just a rough comparison. The point is that it's bigger then you could ever reasonably compute.

ppeterka Over a year ago

I didn't write to disagree, or pick nits, I'd totally consider numbers of this magnitue useless for just about anything... Frankly, I can not think of any practical use...

Peter Lawrey Over a year ago

There isn't a practical use for numbers above 10^100 IMHO. And in the real world you can't measure many constants better than to 13 digits. So really a double is all you need in the real world. ;)

Ingo Over a year ago

@wutzebaer 256 is not a 256 bit number, it is a 8 bit number. We are speaking of numbers that have 2^256 or 10^77 as exponent.

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