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LibJS: Implement Temporal.Calendar.prototype.dayOfWeek

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Idan Horowitz 2021-07-23 17:46:20 +03:00 • committed by Linus Groh
parent 59dc0e8421
commit 339b0a17e8
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20
Userland/Libraries/LibJS/Runtime/Temporal/Calendar.cpp
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@ -386,6 +386,26 @@ i32 iso_days_in_month(i32 year, i32 month)
return 28;
}
// 12.1.33 ToISODayOfWeek ( year, month, day ), https://tc39.es/proposal-temporal/#sec-temporal-toisodayofweek
u8 to_iso_day_of_week(i32 year, u8 month, u8 day)
{
// 1. Assert: year is an integer.
// 2. Assert: month is an integer.
// 3. Assert: day is an integer.
// 4. Let date be the date given by year, month, and day.
// 5. Return date's day of the week according to ISO-8601.
// NOTE: Implemented based on https://cs.uwaterloo.ca/~alopez-o/math-faq/node73.html
auto normalized_month = month + (month < 3 ? 10 : -2);
auto normalized_year = year - (month < 3 ? 1 : 0);
auto century = normalized_year / 100;
auto truncated_year = normalized_year - (century * 100);
auto result = (day + static_cast<u8>((2.6 * normalized_month) - 0.2) - (2 * century) + truncated_year + (truncated_year / 4) + (century / 4)) % 7;
if (result <= 0) // Mathematical modulo
result += 7;
return result;
}
// 12.1.36 BuildISOMonthCode ( month ), https://tc39.es/proposal-temporal/#sec-buildisomonthcode
String build_iso_month_code(i32 month)
{