Re: Predictable Internet Time

Joe Touch <touch@isi.edu> Wed, 04 January 2017 18:11 UTC

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Subject: Re: Predictable Internet Time
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From: Joe Touch <touch@isi.edu>
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Date: Wed, 4 Jan 2017 10:11:06 -0800
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On 1/3/2017 11:14 PM, Patrik Fältström wrote:
> Well, if you look at the POSIX definition you see that it is clearly wrong the days when leap second is added:
>
> tm_sec + tm_min*60 + tm_hour*3600 + tm_yday*86400 +
>     (tm_year-70)*31536000 + ((tm_year-69)/4)*86400 -
>     ((tm_year-1)/100)*86400 + ((tm_year+299)/400)*86400
>
>
> 2015-12-31 23:59:58 365th day 61409923198
> 2015-12-31 23:59:59 365th	 day 61409923199
> 2016-01-01 00:00:00   1st day 61409836800
> 2016-01-01 00:00:01   1st day 61409836801
> 									
> 2016-12-31 23:59:59 366th day 61441459199
> 2016-12-31 23:59:60 366th day 61441459200
> 2017-01-01 00:00:00   1st day 61441459200
> 2017-01-01 00:00:01   1st day 61441459201
>
> I.e. the real problem we have is a broken POSIX definition.
It's as correct as it claims to be - it's an approximation.

If anyone cares about a more precise back-calculation of Unix epoch from
UTC, they would definitely need to consult a leap-second file.

Joe