Is there a library or other way to do 128-bit math operations?

Question

I am writing a cryptography application and need to work with 128 bit integers.

In addition to standard add, subtract, multiply, divide, and comparisons, I also need a power and modulo function as well.

Does anyone know of a library or other implementation that can do this? If not 128-bit, is there a 64-bit option available?

Answer 1

Check out the GNU Multiple Precision Arithmetic Library.

Answer 2

Most any modern compiler is going to provide at least 64 bit through the use of the long long type.

Answer 3

gcc supports uint128_t, which is a 128-bit integer, though this isn't very portable.

Since I don't know any main stream cryptosystems that use 128-bit modular arithmetic, I'm wondering what scheme you are implementing.

Answer 4

Look for the Montgomery algorithms for multiplication and powers in a finite field. I don't know any library but I am quiet sure there are.