BigInteger returning negative numbers

Question

why this math return negative numbers for some numbers:

int x = 351;

    String bigValue= ((50*x*x*x-150*x*x+400*x)/3) + "";
    BigInteger resultInteger = new BigInteger(bigValue);
    System.out.println(resultInteger);

result -> 714612600

but if i use 352

result -> -710900565

for x=500 -> 639244234

WHY?

You are multiplying and dividing by integers which will overflow at some point. — Jeroen Vannevel, Jun 14 '14 at 19:21

Anubian Noob · Answer 1 · 2014-06-15T00:31:10.947

6

This line here:

(50*x*x*x-150*x*x+400*x)/3

Is using integers, which can overflow. If an integer hits the max (2^31-1), it will overflow to -2^31.

You need to use BigIntegers here, something like this:

Biginteger bx = new BigInteger(x);
BigInteger new BigInteger(50).multiply(bx.pow(3)).multiply(new BigInteger(-150))
    .multiply(bx.pow(2)).multiply(new BigInteger(400)).multiply(bx).divide(3);

edited Jun 15 '14 at 00:31

answered Jun 14 '14 at 19:22

Anubian Noob

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so its impossible to do this math? how can i print a very long result? and why for 352 it overflow, and for 500 not? – user2582318 Jun 14 '14 at 19:23
I'm updating my answer, give me a second. – Anubian Noob Jun 14 '14 at 19:24
2

@user2582318 You can use `BigInteger`. By using the `BigInteger` methods, not `new BigInteger(String)` – Justin Jun 14 '14 at 19:24
1

It is 2^31-1 to -2^31 for 32bit signed integers. – Lutz Lehmann Jun 15 '14 at 00:22
@LutzL Thanks, I forgot about the sign bit. – Anubian Noob Jun 15 '14 at 00:31

BigInteger returning negative numbers

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