If you want a guaranteed 64-bit type, put in your code: #include <stdint.h> then, use uint64_t for unsigned and int64_t for signed. If you want 128 bits, in g

If you want a guaranteed 64-bit type, put in your code: #include <stdint.h> then, use uint64_t for unsigned and int64_t for signed. If you want 128 bits, in gcc you can use __uint128_t (it has two extra underscores at the beginning because that size is nonstandard), but I don't think there is support for 256 bit integers. Try a big integer library: http://stackoverflow.com/questions/124332/c-handling-very-large-integers http://stackoverflow.com/questions/124332/c-handling-very-la...