&gt; I&#x27;ve read that if one uses int64_t with a compiler that targets a 32 bit system, doing various operations on the int64_t variable will be much slower because more machine code instructions need to be generated.<p>Yep, but presumably you picked int64_t for a reason. If you want a 32-bit variable, use int32_t.<p>It would be an extremely rare platform on which int16_t is noticeably slower than int. The very minor platform-specific performance improvement you might get from using int rather than int16_t is very rarely worth the risk of introducing an overflow on the few platforms where int is 16 bits[1], and not noticing it because int is longer than that on the platform you develop on.<p>[1]  remember that a signed integer overflow is undefined behaviour which should be regarded as equivalent to a security flaw - the compiler is permitted to send all data your program has access to to the mafia if your program contains a signed integer overflow anywhere, and some compilers will