Insane complexity of calendrically correct date and time operations
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Insane complexity of calendrically correct date and time operations
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Re: Insane complexity of calendrically correct date and time operations
#2Is it true that Unix time is as simple as it seems? Is there exactly one second between adjacent integers? Do all Unix time values occur only once simultaneously around the world?
Re: Insane complexity of calendrically correct date and time operations
#3Is it true that Unix time is as simple as it seems? Is there exactly one second between adjacent integers? Do all Unix time values occur only once simultaneously around the world?
No, because unix times can repeat in the case of leap-seconds (this is necessary to be able to represent future times correctly).
Re: Insane complexity of calendrically correct date and time operations
#4Is it true that Unix time is as simple as it seems? Is there exactly one second between adjacent integers? Do all Unix time values occur only once simultaneously around the world?
What you want is probably TAI [1], Unix Time has leap seconds.
Re: Insane complexity of calendrically correct date and time operations
#5The Problem with Time & Timezones - Computerphile
https://www.youtube.com/watch?v=-5wpm-gesOY
A fantastic overview of the headaches you'd have if you wanted to code all this.
Re: Insane complexity of calendrically correct date and time operations
#6Is it true that Unix time is as simple as it seems? Is there exactly one second between adjacent integers? Do all Unix time values occur only once simultaneously around the world?
Unix time depends on the wall clock time, so it is a wall clock time, so it can jump around arbitrarily when the computer clock is adjusted, and its seconds can be stretched as needed for gliding adjustments. Applications need to cope with that.
Re: Insane complexity of calendrically correct date and time operations
#7Many of these make the weird assumption that you want to support multiple calendars. For better or worse, this is rarely the case.
Re: Insane complexity of calendrically correct date and time operations
#8Is it true that Unix time is as simple as it seems? Is there exactly one second between adjacent integers? Do all Unix time values occur only once simultaneously around the world?
No, because unix times can repeat in the case of leap-seconds (this is necessary to be able to represent future times correctly).
You can avoid repetitions by using clock_gettime(CLOCK_MONOTONIC, …).
Re: Insane complexity of calendrically correct date and time operations
#9This could very well have been called “Falsehoods programmers believe about date and time calculations”. It fits very well into the pattern of other similarly titled lists which have been published in recent years.
Re: Insane complexity of calendrically correct date and time operations
#10Many of these make the weird assumption that you want to support multiple calendars. For better or worse, this is rarely the case.
Yes, or that you care about historical aspects.
If we go on a far enough time scale, all calendars are constructed abstractions so theoretically nothing about them is true, but I'm not sure what's the point of that.