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LibC: Implement gmtime() and localtime() 

localtime() just returns gmtime() as there is no timezone support
This commit is contained in:
Bananymous 2024-06-17 16:51:41 +03:00
parent 9c5cca784e
commit dafd2fecf7
1 changed files with 54 additions and 0 deletions
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54
libc/time.cpp
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@ -21,3 +21,57 @@ time_t time(time_t* tloc)
*tloc = tp.tv_sec;
return tp.tv_sec;
}
struct tm* gmtime(const time_t* timer)
{
static struct tm tm;
constexpr auto is_leap_year =
[](time_t year) -> bool
{
if (year % 400 == 0)
return true;
if (year % 100 == 0)
return false;
if (year % 4 == 0)
return true;
return false;
};
constexpr uint64_t month_days[] { 0, 31, 59, 90, 120, 151, 181, 212, 243, 273, 304, 334, 365 };
time_t time = *timer;
tm.tm_sec = time % 60; time /= 60;
tm.tm_min = time % 60; time /= 60;
tm.tm_hour = time % 24; time /= 24;
time_t total_days = time;
tm.tm_wday = (total_days + 4) % 7;
tm.tm_year = 1970;
while (total_days >= 365U + is_leap_year(tm.tm_year))
{
total_days -= 365U + is_leap_year(tm.tm_year);
tm.tm_year++;
}
bool is_leap_day = is_leap_year(tm.tm_year) && total_days == month_days[2];
bool had_leap_day = is_leap_year(tm.tm_year) && total_days > month_days[2];
for (tm.tm_mon = 0; tm.tm_mon < 12; tm.tm_mon++)
if (total_days < month_days[tm.tm_mon + 1] + (is_leap_day || had_leap_day))
break;
tm.tm_mday = total_days - month_days[tm.tm_mon] + !had_leap_day;
tm.tm_yday = total_days;
tm.tm_year -= 1900;
tm.tm_isdst = 0;
return &tm;
}
struct tm* localtime(const time_t* timer)
{
// FIXME: support timezones
return gmtime(timer);
}