I prefer signed time types, because you frequently subtract them. If you use unsigned, then you have to cast the result to signed every time: int64_t elapsed

I prefer signed time types, because you frequently subtract them. If you use unsigned, then you have to cast the result to signed every time: int64_t elapsed = (int64_t)(t1 - t0); And it's very easy to cause disaster with: if ((t1 - t0) > 50) ... which also succeeds if t1<t0. While it's theoretically possible, using all 64 bits is tricky and very hard to test.