title: Undefined behavior when exceed 64 bits
body: <p>In my current 32-bit application, I check (very occasionally) for overflow by doing operations on 64-bit integers.</p>
  
  <p>However, on 64-bit systems there does not seem to be a standard 128-bit integer. Is there a simple way of checking for overflow, or a way of getting 128-bit integers, which works on all OSes and compilers?</p>
  
  <p>I tried using GMP as a more generic solution, but it is a little heavyweight for my requirements.</p>
  
  <p>Efficiency is not too important, no processor specific-ASM is.</p>