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LibJS: Fix leap year check in to_iso_week_of_year() for week < 1

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When the resulting week is in the previous year, we need to check if the
previous year is a leap year and can potentially have 53 weeks, instead
of the given year.
Also added a comment to briefly explain what's going on, as it took me a
while to figure out.
This commit is contained in:
Linus Groh 2021-11-15 21:21:43 +00:00
parent b7af536f9b
commit a757f3f421
1 changed files with 5 additions and 1 deletions
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6
Userland/Libraries/LibJS/Runtime/Temporal/Calendar.cpp
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@ -700,8 +700,12 @@ u8 to_iso_week_of_year(i32 year, u8 month, u8 day)
auto week = (day_of_year - day_of_week + 10) / 7;
if (week < 1) {
// NOTE: The resulting week is actually part of the previous year. If that year ends with a
// Thursday (i.e. the first day of the given year is a Friday, or day 5), or the previous
// year is a leap year and ends with a Friday (i.e. the first day of the given year is a
// Saturday, or day 6), it has 53 weeks, and 52 weeks otherwise.
auto day_of_jump = to_iso_day_of_week(year, 1, 1);
if (day_of_jump == 5 || (is_iso_leap_year(year) && day_of_jump == 6))
if (day_of_jump == 5 || (is_iso_leap_year(year - 1) && day_of_jump == 6))
return 53;
else
return 52;