Re: [Emacs-diffs] master 6cfda69 1/2: Add support for dealing with decoded time structures

[Paul Eggert]

> > > +(defun date-days-in-month (year month)
> > > +  "The number of days in MONTH in YEAR."
> > > +  (if (= month 2)
> > > +      (if (date-leap-year-p year)
> > > +          29
> > > +        28)
> > > +    (if (memq month '(1 3 5 7 8 10 12))
> > > +        31
> > > +      30)))
> >
> > Doesn't this already exist as the Gregorian calendar-last-day-of-month
> > in calendar.el?
>
> Yes, apparently.  (I didn't know about it.)

The two functions are not equivalent, as date-days-in-month uses astronomical 
year numbering, whereas calendar-last-day-of-month uses traditional year 
numbering, with no year zero.