How can I add and subtract 128 bit integers in C or C++ if my compiler does not support them?

Question

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 th

Answer 1

Also worth noting: if the goal is merely to improve the compression of a stream of numbers by preprocessing it, then the preprocessed stream doesn't have to be made of exactly arithmetic differences. You can use XOR (^) instead of + and -. The advantage is that a 128-bit XOR is exactly the same as two independent XORs on the 64-bit parts, so it is both simple and efficient.