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sortix--sortix/libc/time/gmtime_r.cpp
Jonas 'Sortie' Termansen 2c164844f2 Add mktime(3).
2013-12-17 14:30:34 +01:00

292 lines
7.3 KiB
C++

/*******************************************************************************
Copyright(C) Jonas 'Sortie' Termansen 2013.
This file is part of the Sortix C Library.
The Sortix C Library is free software: you can redistribute it and/or modify
it under the terms of the GNU Lesser General Public License as published by
the Free Software Foundation, either version 3 of the License, or (at your
option) any later version.
The Sortix C Library is distributed in the hope that it will be useful, but
WITHOUT ANY WARRANTY; without even the implied warranty of MERCHANTABILITY
or FITNESS FOR A PARTICULAR PURPOSE. See the GNU Lesser General Public
License for more details.
You should have received a copy of the GNU Lesser General Public License
along with the Sortix C Library. If not, see <http://www.gnu.org/licenses/>.
time/gmtime_r.cpp
Convert a timestamp into a date and time according to UTC.
*******************************************************************************/
#include <time.h>
#include <stdint.h>
#include <time.h>
static const int DAYS_JANUARY = 31;
static const int DAYS_FEBRUARY = 28;
static const int DAYS_MARCH = 31;
static const int DAYS_APRIL = 30;
static const int DAYS_MAY = 31;
static const int DAYS_JUNE = 30;
static const int DAYS_JULY = 31;
static const int DAYS_AUGUST = 31;
static const int DAYS_SEPTEMBER = 30;
static const int DAYS_OCTOBER = 31;
static const int DAYS_NOVEMBER = 30;
static const int DAYS_DECEMBER = 31;
#define DECL_LEAP_SECOND(year, jun, dec) \
{0, 0, 0, 0, 0, jun, 0, 0, 0, 0, 0, dec}
static int8_t leap_seconds[][12] =
{
DECL_LEAP_SECOND(1970, 0, 0),
DECL_LEAP_SECOND(1971, 0, 0),
DECL_LEAP_SECOND(1972, 0, 0),
DECL_LEAP_SECOND(1972, 1, 1),
DECL_LEAP_SECOND(1973, 0, 1),
DECL_LEAP_SECOND(1974, 0, 1),
DECL_LEAP_SECOND(1975, 0, 1),
DECL_LEAP_SECOND(1976, 0, 1),
DECL_LEAP_SECOND(1977, 0, 1),
DECL_LEAP_SECOND(1978, 0, 1),
DECL_LEAP_SECOND(1979, 0, 1),
DECL_LEAP_SECOND(1980, 0, 0),
DECL_LEAP_SECOND(1981, 1, 0),
DECL_LEAP_SECOND(1982, 1, 0),
DECL_LEAP_SECOND(1983, 1, 0),
DECL_LEAP_SECOND(1984, 0, 0),
DECL_LEAP_SECOND(1985, 1, 0),
DECL_LEAP_SECOND(1986, 0, 0),
DECL_LEAP_SECOND(1987, 0, 1),
DECL_LEAP_SECOND(1988, 0, 0),
DECL_LEAP_SECOND(1989, 0, 1),
DECL_LEAP_SECOND(1990, 0, 1),
DECL_LEAP_SECOND(1991, 0, 0),
DECL_LEAP_SECOND(1992, 1, 0),
DECL_LEAP_SECOND(1993, 1, 0),
DECL_LEAP_SECOND(1994, 1, 0),
DECL_LEAP_SECOND(1995, 0, 1),
DECL_LEAP_SECOND(1996, 0, 0),
DECL_LEAP_SECOND(1997, 1, 0),
DECL_LEAP_SECOND(1998, 0, 1),
DECL_LEAP_SECOND(1999, 0, 0),
DECL_LEAP_SECOND(2000, 0, 0),
DECL_LEAP_SECOND(2001, 0, 0),
DECL_LEAP_SECOND(2002, 0, 0),
DECL_LEAP_SECOND(2003, 0, 0),
DECL_LEAP_SECOND(2004, 0, 0),
DECL_LEAP_SECOND(2005, 0, 1),
DECL_LEAP_SECOND(2006, 0, 0),
DECL_LEAP_SECOND(2007, 0, 0),
DECL_LEAP_SECOND(2008, 0, 1),
DECL_LEAP_SECOND(2009, 0, 0),
DECL_LEAP_SECOND(2010, 0, 0),
DECL_LEAP_SECOND(2011, 0, 0),
DECL_LEAP_SECOND(2012, 1, 0),
DECL_LEAP_SECOND(2013, 0, 0),
};
static time_t get_leap_second(int year, int month)
{
const time_t num_years = sizeof(leap_seconds) / sizeof(leap_seconds[0]);
if ( year < 1970 )
return 0;
if ( num_years <= year-1970 )
return 0;
return leap_seconds[year-1970][month];
}
static time_t leap_seconds_in_year(int year)
{
time_t ret = 0;
for ( int i = 0; i < 12; i++ )
ret += get_leap_second(year, i);
return ret;
}
static bool is_leap_year(int year)
{
return (year % 4 == 0 && year % 100 != 0) || year % 400 == 0;
}
static time_t days_in_year(int year)
{
return DAYS_JANUARY +
DAYS_FEBRUARY + (is_leap_year(year) ? 1 : 0) +
DAYS_MARCH +
DAYS_APRIL +
DAYS_MAY +
DAYS_JUNE +
DAYS_JULY +
DAYS_AUGUST +
DAYS_SEPTEMBER +
DAYS_OCTOBER +
DAYS_NOVEMBER +
DAYS_DECEMBER;
}
extern "C" struct tm* gmtime_r(const time_t* time_ptr, struct tm* ret)
{
time_t left = *time_ptr;
ret->tm_year = 1970;
ret->tm_wday = 4 /* Supposedly, the world began on a Thursday. */;
// If the timestamp is after the epoch.
while ( 0 < left )
{
time_t year_leaps = leap_seconds_in_year(ret->tm_year);
time_t year_days = days_in_year(ret->tm_year);
time_t year_seconds = year_days * 24 * 60 * 60 + year_leaps;
if ( year_seconds <= left )
{
left -= year_seconds;
ret->tm_wday = (ret->tm_wday + year_days) % 7;
ret->tm_year++;
continue;
}
break;
}
// If the timestamp was before the epoch.
while ( left < 0 )
{
ret->tm_year--;
time_t year_leaps = leap_seconds_in_year(ret->tm_year);
time_t year_days = days_in_year(ret->tm_year);
time_t year_seconds = year_days * 24 * 60 * 60 + year_leaps;
left += year_seconds;
// We need to avoid taking the modulo of a negative value or the
// (broken) C modulo operator gives the wrong result.
ret->tm_wday = (ret->tm_wday - year_days + 7*7*7*7) % 7;
}
int month_days_list[12] =
{
DAYS_JANUARY,
DAYS_FEBRUARY + (is_leap_year(ret->tm_year) ? 1 : 0),
DAYS_MARCH,
DAYS_APRIL,
DAYS_MAY,
DAYS_JUNE,
DAYS_JULY,
DAYS_AUGUST,
DAYS_SEPTEMBER,
DAYS_OCTOBER,
DAYS_NOVEMBER,
DAYS_DECEMBER,
};
// Figure out the correct month.
ret->tm_mon = 0;
ret->tm_yday = 0;
while ( true )
{
int month_leaps = get_leap_second(ret->tm_year, ret->tm_mon);
int month_days = month_days_list[ret->tm_mon];
int month_seconds = month_days * 24 * 60 * 60 + month_leaps;
if ( month_seconds <= left )
{
left -= month_seconds;
ret->tm_mon++;
ret->tm_yday += month_days;
ret->tm_wday = (ret->tm_wday + month_days) % 7;
continue;
}
break;
}
ret->tm_mday = left / (24 * 60 * 60);
left = left % (24 * 60 * 60);
// If this is a regular timestamp.
if ( ret->tm_mday < month_days_list[ret->tm_mon] )
{
ret->tm_yday += ret->tm_mday;
ret->tm_hour = left / (60 * 60);
left = left % (60 * 60);
ret->tm_min = left / 60;
left = left % 60;
ret->tm_sec = left;
}
// If we got the timestamp for an added leap second.
else
{
ret->tm_mday--; // Seemingly additional day.
ret->tm_yday += ret->tm_mday;
ret->tm_hour = 23;
ret->tm_min = 59;
ret->tm_sec = 60;
}
ret->tm_wday = (ret->tm_wday + ret->tm_mday) % 7;
// TODO: Support daylight savings and timezones.
ret->tm_isdst = -1;
// Fix the ranges of some of the variables.
ret->tm_mday += 1;
ret->tm_year -= 1900;
return ret;
}
extern "C" time_t timegm(struct tm* tm)
{
time_t year = tm->tm_year + 1900;
time_t month = tm->tm_mon;
time_t day = tm->tm_mday - 1;
time_t hour = tm->tm_hour;
time_t minute = tm->tm_min;
time_t second = tm->tm_sec;
time_t ret = 0;
for ( time_t y = 1970; y < year; y++ )
{
time_t year_leaps = leap_seconds_in_year(y);
time_t year_days = days_in_year(y);
time_t year_seconds = year_days * 24 * 60 * 60 + year_leaps;
ret += year_seconds;
}
int month_days_list[12] =
{
DAYS_JANUARY,
DAYS_FEBRUARY + (is_leap_year(year) ? 1 : 0),
DAYS_MARCH,
DAYS_APRIL,
DAYS_MAY,
DAYS_JUNE,
DAYS_JULY,
DAYS_AUGUST,
DAYS_SEPTEMBER,
DAYS_OCTOBER,
DAYS_NOVEMBER,
DAYS_DECEMBER,
};
for ( uint8_t m = 0; m < month; m++ )
{
int month_leaps = get_leap_second(year, m);
int month_days = month_days_list[m];
int month_seconds = month_days * 24 * 60 * 60 + month_leaps;
ret += month_seconds;
}
ret += (time_t) day * 24 * 60 * 60;
ret += (time_t) hour * 60 * 60;
ret += (time_t) minute * 60;
ret += (time_t) second * 1;
return ret;
}