[PATCH] RTC: Add rtc_year_days() to calculate tm_yday

RTC: Add exported function rtc_year_days() to calculate the tm_yday value.
Signed-off-by: Andrew Victor <andrew@sanpeople.com>
Signed-off-by: Alessandro Zummo <a.zummo@towertech.it>
Cc: Russell King <rmk@arm.linux.org.uk>
Signed-off-by: Andrew Morton <akpm@osdl.org>
Signed-off-by: Linus Torvalds <torvalds@osdl.org>

drivers/rtc/rtc-lib.c

@@ -18,15 +18,34 @@ static const unsigned char rtc_days_in_month[] = {
 	31, 28, 31, 30, 31, 30, 31, 31, 30, 31, 30, 31
 };
 
+static const unsigned short rtc_ydays[2][13] = {
+	/* Normal years */
+	{ 0, 31, 59, 90, 120, 151, 181, 212, 243, 273, 304, 334, 365 },
+	/* Leap years */
+	{ 0, 31, 60, 91, 121, 152, 182, 213, 244, 274, 305, 335, 366 }
+};
+
 #define LEAPS_THRU_END_OF(y) ((y)/4 - (y)/100 + (y)/400)
 #define LEAP_YEAR(year) ((!(year % 4) && (year % 100)) || !(year % 400))
 
+/*
+ * The number of days in the month.
+ */
 int rtc_month_days(unsigned int month, unsigned int year)
 {
 	return rtc_days_in_month[month] + (LEAP_YEAR(year) && month == 1);
 }
 EXPORT_SYMBOL(rtc_month_days);
 
+/*
+ * The number of days since January 1. (0 to 365)
+ */
+int rtc_year_days(unsigned int day, unsigned int month, unsigned int year)
+{
+	return rtc_ydays[LEAP_YEAR(year)][month] + day-1;
+}
+EXPORT_SYMBOL(rtc_year_days);
+
 /*
  * Convert seconds since 01-01-1970 00:00:00 to Gregorian date.
  */

include/linux/rtc.h

@@ -102,6 +102,7 @@ struct rtc_pll_info {
 #include <linux/interrupt.h>
 
 extern int rtc_month_days(unsigned int month, unsigned int year);
+extern int rtc_year_days(unsigned int day, unsigned int month, unsigned int year);
 extern int rtc_valid_tm(struct rtc_time *tm);
 extern int rtc_tm_to_time(struct rtc_time *tm, unsigned long *time);
 extern void rtc_time_to_tm(unsigned long time, struct rtc_time *tm);