[libc] Add mktime() function

Signed-off-by: Michael Brown <mcb30@ipxe.org>

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;
+}