[zzo38computer]

My opinion is to use a dual structure which is how I had considered in my operating system design: a signed 64-bit (or possibly longer) number of seconds, and a 32-bit number of nanoseconds (which is not always present; sometimes the precision of nanoseconds is unknown or unnecessary, so it would be omitted). There are then separate subtypes of timestamps, such as UTC (which allows the number of nanoseconds to exceed one billion) and SI (which does not allow the number of nanoseconds to exceed one billion). Which is appropriate depends on the application.

[bloppe]

That's an interesting approach, but not without pitfalls. You can't just subtract two timestamps to get a time difference, since there may have been one with 2 billion nanoseconds somewhere in between.

[zzo38computer]

This is true. However:

- You can subtract two SI-based timestamps to get a SI-based time difference. This will give you the correct number of nanoseconds.

- You can subtract two UTC-based timestamps to get a UTC-based time difference. This will not give you a number of nanoseconds.

Note that, if you have a list of when leap seconds are, then you can convert between SI-based and UTC-based timestamps which are counted from the epoch; in this way it is possible to get a SI-based time difference from UTC-based timestamps if you need it.

It is not as simple as just subtracting them of course, but if your application is meant to use precise time differences then you can just use SI-based timestamps instead of UTC-based timestamps, so that you can simply subtract them from each other. Programs that need to deal with days and calendars instead, are likely to prefer to use UTC-based timestamps instead.