title: How can I add and subtract 128 bit integers in C or C++ if my compiler does not support them?
body: <p>I'm writing a compressor for a long stream of 128 bit numbers. I would like to store the numbers as differences -- storing only the difference between the numbers rather than the numbers themselves because I can pack the differences in fewer bytes because they are smaller.</p>
  
  <p>However, for compression then I need to subtract these 128 bit values, and for decompression I need to add these values. Maximum integer size for my compiler is 64 bits wide.</p>
  
  <p>Anyone have any ideas for doing this efficiently?</p>