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Diffstat (limited to 'src/core/time.c')
| -rw-r--r-- | src/core/time.c | 137 |
1 files changed, 137 insertions, 0 deletions
diff --git a/src/core/time.c b/src/core/time.c new file mode 100644 index 00000000..52ae3ee9 --- /dev/null +++ b/src/core/time.c @@ -0,0 +1,137 @@ +/* + * Copyright (C) 2012 Michael Brown <mbrown@fensystems.co.uk>. + * + * This program is free software; you can redistribute it and/or + * modify it under the terms of the GNU General Public License as + * published by the Free Software Foundation; either version 2 of the + * License, or any later version. + * + * This program 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 + * General Public License for more details. + * + * You should have received a copy of the GNU General Public License + * along with this program; if not, write to the Free Software + * Foundation, Inc., 675 Mass Ave, Cambridge, MA 02139, USA. + */ + +FILE_LICENCE ( GPL2_OR_LATER ); + +#include <time.h> + +/** @file + * + * Date and time + * + * POSIX:2008 section 4.15 defines "seconds since the Epoch" as an + * abstract measure approximating the number of seconds that have + * elapsed since the Epoch, excluding leap seconds. The formula given + * is + * + * tm_sec + tm_min*60 + tm_hour*3600 + tm_yday*86400 + + * (tm_year-70)*31536000 + ((tm_year-69)/4)*86400 - + * ((tm_year-1)/100)*86400 + ((tm_year+299)/400)*86400 + * + * This calculation assumes that leap years occur in each year that is + * either divisible by 4 but not divisible by 100, or is divisible by + * 400. + */ + +/** Days of week (for debugging) */ +static const char *weekdays[] = { + "Sun", "Mon", "Tue", "Wed", "Thu", "Fri", "Sat" +}; + +/** + * Determine whether or not year is a leap year + * + * @v tm_year Years since 1900 + * @v is_leap_year Year is a leap year + */ +static int is_leap_year ( int tm_year ) { + int leap_year = 0; + + if ( ( tm_year % 4 ) == 0 ) + leap_year = 1; + if ( ( tm_year % 100 ) == 0 ) + leap_year = 0; + if ( ( tm_year % 400 ) == 100 ) + leap_year = 1; + + return leap_year; +} + +/** + * Calculate number of leap years since 1900 + * + * @v tm_year Years since 1900 + * @v num_leap_years Number of leap years + */ +static int leap_years_to_end ( int tm_year ) { + int leap_years = 0; + + leap_years += ( tm_year / 4 ); + leap_years -= ( tm_year / 100 ); + leap_years += ( ( tm_year + 300 ) / 400 ); + + return leap_years; +} + +/** + * Calculate day of week + * + * @v tm_year Years since 1900 + * @v tm_mon Month of year [0,11] + * @v tm_day Day of month [1,31] + */ +static int day_of_week ( int tm_year, int tm_mon, int tm_mday ) { + static const uint8_t offset[12] = + { 1, 4, 3, 6, 1, 4, 6, 2, 5, 0, 3, 5 }; + int pseudo_year = tm_year; + + if ( tm_mon < 2 ) + pseudo_year--; + return ( ( pseudo_year + leap_years_to_end ( pseudo_year ) + + offset[tm_mon] + tm_mday ) % 7 ); +} + +/** Days from start of year until start of months (in non-leap years) */ +static const uint16_t days_to_month_start[] = + { 0, 31, 59, 90, 120, 151, 181, 212, 243, 273, 304, 334 }; + +/** + * Calculate seconds since the Epoch + * + * @v tm Broken-down time + * @ret time Seconds since the Epoch + */ +time_t mktime ( struct tm *tm ) { + int days_since_epoch; + int seconds_since_day; + time_t seconds; + + /* Calculate day of year */ + tm->tm_yday = ( ( tm->tm_mday - 1 ) + + days_to_month_start[ tm->tm_mon ] ); + if ( ( tm->tm_mon >= 2 ) && is_leap_year ( tm->tm_year ) ) + tm->tm_yday++; + + /* Calculate day of week */ + tm->tm_wday = day_of_week ( tm->tm_year, tm->tm_mon, tm->tm_mday ); + + /* Calculate seconds since the Epoch */ + days_since_epoch = ( tm->tm_yday + ( 365 * tm->tm_year ) - 25567 + + leap_years_to_end ( tm->tm_year - 1 ) ); + seconds_since_day = + ( ( ( ( tm->tm_hour * 60 ) + tm->tm_min ) * 60 ) + tm->tm_sec ); + seconds = ( ( ( ( time_t ) days_since_epoch ) * ( ( time_t ) 86400 ) ) + + seconds_since_day ); + + DBGC ( &weekdays, "TIME %04d-%02d-%02d %02d:%02d:%02d => %lld (%s, " + "day %d)\n", ( tm->tm_year + 1900 ), ( tm->tm_mon + 1 ), + tm->tm_mday, tm->tm_hour, tm->tm_min, tm->tm_sec, seconds, + weekdays[ tm->tm_wday ], tm->tm_yday ); + + return seconds; +} |