Question

I have a c++ BigInteger library. I have to create a bigInteger with exact 125 bit from any large random number. I need to perform rightshift, leftshift, setbit, getbit, NOT, OR, XOR, AND operation on created 125 bit number. Which library i need to use to do above operation? Can anyone please help me.

Answer 1

A google search with the terms big integer library gave me the C++ Big Integer Library . From the website:

This library emphasizes ease of use and clarity of implementation over
speed; some users will prefer GMP, which is faster.

Edit:

To create a random number with 125 bits there are plenty of options.

A simple and quick solution (but obviously not available in the library I posted above – I don’t whether it’s possible with GMP) would be to do a rand() * 0x1FFFFFFFFFFFFFFFFFFFFFFFFFFFFFFF in the correct notation.

A method in the scope of the above library, which unfortunately is rather slow, would be to draw 125 single bits (“0” or “1” at random) and add increasing powers of 2 if you drew a “1”. Here is some (untested) code:

BigInteger summand, number125bit;
summand = 1;

srand(systemtime_or_any_other_number);
for (int i=0; i<125; i++)
{
    if (rand() && 1)
    {
         number125bit += summand;
    }
    summand = summand << 1;
}