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Improve ISO week-base-year formatter

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This commit is contained in:
Vladislav Shchapov
2021-10-10 19:52:02 +05:00
committed by Victor Zverovich
parent fbaaa5906b
commit 79c00ad8f2
2 changed files with 68 additions and 6 deletions
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36
include/fmt/chrono.h
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@@ -1425,10 +1425,37 @@ template <typename FormatContext, typename OutputIt> struct tm_formatter {
}
return {q, r};
}
// Algorithm:
// https://en.wikipedia.org/wiki/ISO_week_date#Calculating_the_week_number_from_a_month_and_day_of_the_month_or_ordinal_date
struct iso_weak {
int year;
int woy;
};
auto tm_iso_year_weaks(int year) -> int {
int p = (year + year / 4 - year / 100 + year / 400) % daysperweek;
int year_1 = year - 1;
int p_1 = (year_1 + year_1 / 4 - year_1 / 100 + year_1 / 400) % daysperweek;
return 52 + ((p == 4 || p_1 == 3) ? 1 : 0);
}
auto tm_iso_weak() -> iso_weak {
auto year = tm_year();
int w = (tm.tm_yday + 10 - (tm.tm_wday == 0 ? daysperweek : tm.tm_wday)) /
daysperweek;
if (w < 1) {
return {year - 1, tm_iso_year_weaks(year - 1)};
} else if (w > tm_iso_year_weaks(year)) {
return {year + 1, 1};
} else {
return {year, w};
}
}
auto tm_hour12() const -> decltype(tm.tm_hour) {
auto hour = tm.tm_hour % 12;
return hour == 0 ? 12 : hour;
}
void write1(size_t value) { *out++ = detail::digits2(value)[1]; }
void write2(size_t value) {
out = std::copy_n(detail::digits2(value), 2, out);
@@ -1575,19 +1602,16 @@ template <typename FormatContext, typename OutputIt> struct tm_formatter {
}
void on_iso_week_of_year(numeric_system ns) {
if (ns == numeric_system::standard) {
// TODO: Optimization
format_localized('V');
write2(detail::to_unsigned(tm_iso_weak().woy));
} else {
format_localized('V', 'O');
}
}
void on_iso_week_based_year() {
// TODO: Optimization
format_localized('G');
out = detail::write<char_type>(out, tm_iso_weak().year);
}
void on_iso_week_based_year_last2() {
// TODO: Optimization
format_localized('g');
write2(detail::to_unsigned(tm_split_year(tm_iso_weak().year).lower));
}
void on_day_of_year() {
auto yday = tm.tm_yday + 1;