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

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

[Andrew Victor]

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>


diff -urN -x CVS linux-2.6.17-rc6/drivers/rtc/rtc-lib.c linux-2.6.17-rc/drivers/rtc/rtc-lib.c
--- linux-2.6.17-rc6/drivers/rtc/rtc-lib.c	Tue Jun  6 10:28:05 2006
+++ linux-2.6.17-rc/drivers/rtc/rtc-lib.c	Wed Jun  7 11:27:49 2006
@@ -18,15 +18,34 @@
 	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.
  */
diff -urN -x CVS linux-2.6.17-rc6/include/linux/rtc.h linux-2.6.17-rc/include/linux/rtc.h
--- linux-2.6.17-rc6/include/linux/rtc.h	Tue Jun  6 10:28:30 2006
+++ linux-2.6.17-rc/include/linux/rtc.h	Wed Jun  7 11:24:45 2006
@@ -102,6 +102,7 @@
 #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);

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

[Russell King]

On Wed, Jun 07, 2006 at 08:26:09PM +0200, Andrew Victor wrote:
> RTC: Add exported function rtc_year_days() to calculate the tm_yday
> value.

Is there a good reason for this?  I ask the question because the x86
/dev/rtc driver says:

         * Only the values that we read from the RTC are set. We leave
         * tm_wday, tm_yday and tm_isdst untouched. Note that while the
         * RTC has RTC_DAY_OF_WEEK, we should usually ignore it, as it is
         * only updated by the RTC when initially set to a non-zero value.

So it seems the established modus operandi for RTC interfaces is "don't
trust wday, yday and isdst".

-- 
Russell King
 Linux kernel    2.6 ARM Linux   - http://www.arm.linux.org.uk/
 maintainer of:  2.6 Serial core

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

[H. Peter Anvin]

Followup to:  <20060607193311.GH13165@flint.arm.linux.org.uk>
By author:    Russell King <rmk+lkml@arm.linux.org.uk>
In newsgroup: linux.dev.kernel
>
> On Wed, Jun 07, 2006 at 08:26:09PM +0200, Andrew Victor wrote:
> > RTC: Add exported function rtc_year_days() to calculate the tm_yday
> > value.
> 
> Is there a good reason for this?  I ask the question because the x86
> /dev/rtc driver says:
> 
>          * Only the values that we read from the RTC are set. We leave
>          * tm_wday, tm_yday and tm_isdst untouched. Note that while the
>          * RTC has RTC_DAY_OF_WEEK, we should usually ignore it, as it is
>          * only updated by the RTC when initially set to a non-zero value.
> 
> So it seems the established modus operandi for RTC interfaces is "don't
> trust wday, yday and isdst".
> 

"Be conservative in what you send, liberal in what you accept."

	- Mr. Protocol

In this case it seems a good idea to set these fields correctly, but
not rely upon them, unless there are known cases where that causes
trouble.

	-hpa

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

[Andrew Victor]

hi Russell,

> > RTC: Add exported function rtc_year_days() to calculate the tm_yday
> > value.
> 
> Is there a good reason for this?  I ask the question because the x86
> /dev/rtc driver says:
> 
>          * Only the values that we read from the RTC are set. We leave
>          * tm_wday, tm_yday and tm_isdst untouched. Note that while the
>          * RTC has RTC_DAY_OF_WEEK, we should usually ignore it, as it is
>          * only updated by the RTC when initially set to a non-zero value.
> 
> So it seems the established modus operandi for RTC interfaces is "don't
> trust wday, yday and isdst".

wday and yday are already being calculated by rtc_time_to_tm() in
drivers/rtc/rtc-lib.c, and this function is used by about half of the
RTC class drivers.

Since yday can also be easily calculated from dd/mm/yyyy, I don't see
why those drivers who don't use rtc_time_to_tm() can't also return a
valid yday value.


Regards,
  Andrew Victor