From: Jeff Garland (jeff_at_[hidden])
Date: 2005-07-17 10:13:45
On Sun, 17 Jul 2005 15:57:21 +0200, Friedrich Wilckens wrote
> date_time::date::day_of_week() calls two functions from the calendar
> template parameter: the first to convert the internal integer
> representation into a ymd_type, and the second to calculate the
> day_of_week for this ymd_type. Both do some non-trivial arithmetic.
True.
> I wonder why the following simpler and more efficient approach is not
> used.
>
> In date_time::date:
>
> day_of_week_type day_of_week() const
> {
> return calendar::day_of_week(days_);
> }
>
> In date_time::gregorian_calendar_base add a method:
>
> static unsigned short day_of_week(const date_int_type& d)
> {
> return (d + 1) % 7;
> }
>
> As far as I know, the sequence of weeks in the gregorian calendar is
> completely regular and this simple calculation is correct.
Yes that's true -- of course the above would have to be some adjustment for
the possibility that day 0 != Sunday...
> This approach would also not limit flexibility of the date template.
> If for another calendar there is some irregularity, we could for
And there is if you wanted to implement an 'accurate' gregorian calendar
instead of a propletic one. You'd have to adjust for all sorts of interesting
adjustments in the 1580's.
> this calendar implement
>
> static unsigned short day_of_week(const date_int_type& d)
> {
> return day_of_week(from_day_number(d));
> }
>
> Is there any problem in this reasoning?
Probably not. I'll put it on the todo list for 1.34.
Thx,
Jeff