[cabfpub] Durations

Ryan Sleevi sleevi at google.com
Mon Feb 6 15:02:57 UTC 2017

On Mon, Feb 6, 2017 at 2:47 AM, Rob Stradling via Public <
public at cabforum.org> wrote:

> I agree with Peter that it would make much more sense to define maximum
> validity periods in terms of numbers of days, not numbers of months.

I'm happy to accommodate this with Ballot 185/186, I suppose I'm somewhat
surprised by it. That is, I would have thought it intuitive that:
July 31 -> Aug 31 = 1 month (31 days)
Jan 1 -> Feb 1 = 1 month (31 days)

Similarly, I would have thought it generally uncontroversial that
Jan 31 -> March 3 != 1 month (despite being 31 days)
May 31 -> July 1 != 1 month (despite being 31 days)

If we thus apply the same logic, we determine that
Jan 31 -> Feb 28 (or 29) == 1 month
May 31 -> June 30 == 1 month

However, this does mean that the definition of "How many days in 13 months"
varies depending on your start day, for the aforementioned reasons, and
that variability is no doubt something that some might have concern with.

For example, this also means that
Feb 28 (or 29) -> March 28 (or 29) == 1 month

I have difficulty with understanding the "it's easier for computers"
argument, since any general date-aware application can apply a rather
simple rule - the difference in years * 12, the difference in months, and
counting any negative difference in days as 'another month'. As Rob
mentioned on the issue, this approach is at least consistent with Oracle's
implementation, and certainly consistent with how we (Google) have
interpreted this requirement.

However, because there's any interpretation involved at all, I'm happy to
defer to days, with the clarification that any difference in the time
period as well becomes considered a full day as well

That is

Jan 1 00:00:00 -> Jan 2 00:00:00 == 1 day
Jan 1 00:00:00 -> Jan 2 00:00:01 > 1 day

(And luckily, the same doesn't have to be said about fractional
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