Bug 3182

Sigh. I thought that one of the main differences between
proprietary software and open source software was

   getting the job done  vs.  getting the job done *right*.

I downloaded the new  timetool-2.5-3  rpm, and took a look
at how it was patched to fix the year-2000-is-a-leap-year
problem.

I was dismayed at the sloppiness. While I am not familiar
with the scripting language it is written in [wish], I can
see that the patch, as well as the original version,
display a basic misunderstanding of the Gregorian calendar.
In particular, both the old and new versions of the program
incorrectly determine the leap status of years such as
1900 and 2100. They are *not* leap years.

The correct rule is:

  Years not divisible by 4 are not leap years.
  Years divisible by 4 but not 100 are leap years.
  Years divisible by 100 but not 400 are not leap years.
  Years divisible by 400 are leap years.

There are many sources for this information. For example, on
a Red Hat distribution with gcal installed, see
/usr/doc/gcal*/doc. Sloppy patches like the one you provided
are the kinds of things that created the Y2K mess in the
first place.

### Here's the relevant code in /usr/bin/timetool from
timetool-2.5-3:

proc days_in_month {} {
    global cl_month cl_year month_length

    if {$cl_month == 2} {
        if {[expr $cl_year / 4.0] != [expr $cl_year / 4]} {
            return 28
        }
        if {[expr $cl_year / 400.0] == [expr $cl_year /
400]} {
            if {$cl_year == 2000} {
                return 29
            } else {
                return 28
            }
        }
        return 29
    } else {
        return $month_length($cl_month)
    }
}

### Here's a better (but untested) solution:

proc days_in_month {} {
    global cl_month cl_year month_length

    if {$cl_month == 2} {
        if {[expr $cl_year / 4.0] != [expr $cl_year / 4]} {
            return 28
        }
        if {[expr $cl_year / 100.0] != [expr $cl_year /
100]} {
            return 29
        }
        if {[expr $cl_year / 400.0] != [expr $cl_year /
400]} {
            return 28
        }
        return 29
    } else {
        return $month_length($cl_month)
    }
}