title: Fastest 128 bit integer library
body: <p>I am working on a CPU-heavy numerical computation app. Without going into many details, it's a computational math research project that involves computing a certain function f(x) for large integer x. </p>
  
  <p>Right now everything is implemented in C++ in x64 mode, using native 64-bit ints. That limits me to x&lt;2^64~1.8*10^19. I want to go further, to do that, I need a library that does 128-bit arithmetic. And it has to be very fast. In particular, integer divisions should be fast. Otherwise I'll be sitting here waiting for the results till Thanksgiving. And I'd rather not reinvent the wheel.</p>
  
  <p>I found a list of ~20 big integer libraries on Wikipedia, but most of those seem to be targeted towards arbitrary-precision numbers, which is overkill for my task, and I don't need extra costs associated with that. </p>
  
  <p>Does anyone know what library can operate on 128 bit integers fastest?</p>