Perhaps you can get the difference in number of days and then do the math on that. Skip to the next post for a summary.
This is the general idea:
We know that there are 7 days in a week.
This means that for every multiple of 7, you will definitely have encountered the weekend.
We then have some remaining days between 0 to 6 inclusively, and depending on which day the update was run, you may run into zero, one, or two off days.
So total working time can be written as
working_time = total_time - (weekends) - (# of off days in remainder)
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The total number of weeks elapsed can be determined by simply dividing total days by 7
weeks = Totaldays / 7
daysOff = weeks * 2 (saturday and sunday)
So immediately, you can take off the hours for those days.
Now we have the remaining days of the week left, which is the remainder (mod function...I think it is the same in crystal)
RemainingDays = Totaldays mod 7
Suppose the last update was 30 days ago. That means you definitely came across 4 weekends, and you're left with 2 days remaining.
If you updated on a friday, then you would've run into the weekend for those 2 days.
Alternatively, if it occurred on a sunday, the next 2 days would be working hours.
You know the day that the update was run, and that day can be represented as a number (1 through 7 I believe, for each day of the week).
The only days you want are 1 through 5; anything else should be subtracted.
Suppose we started on 4. Those two days would be 5 and 6. What if we just took the remainder as well?
(start_date + days_remain) mod weekdays
= (4 + 2 ) mod 5
= 1
That leaves us with 1, which we expect since we run into saturday.
Similarly, suppose we started on friday. It would be (5 + 2) mod 5 = 2, which is expected since we run into sat and sun.
And of course, if we start on say monday, we'd have (1 + 2) mod 5 = 0, which means there were no off days in the remaining period.
So your final formula for determining the number of hours to take off would be
work_time = [totalTime - (weeks off) - (days off)]
work_time = [ttime - (8 * (TotalDays / 7 * 2)) - (8 * (start_day + (Totaldays mod 7) mod 5)]
Or something like that.
That would be the idea from a pure mathematical approach, but here's a case that it fails:
Total days = 34, Update day = friday
4 weeks + 3 days remaining
So my formula claims that (5 + 3) mod 5 = 3 is the number of off days you encounter. Clearly that's not true.
Maybe I'm missing something. There might be an easier solution.
EDIT: some brute force checking:
if start day + remaining >= 7, then we have run into two off days (cause it passed both sat and sun)
If start day + remaining = 6, then we have run into one off day (only sat)
if start day + remaining < 6, then we have run into no off days (didn't even reach saturday)
Edited by Keikoku - 31 May 2011 at 8:30am
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