Applied patch by Julun: time computations based on an algorithm by Fliegel,

and van Flandern (1968), instead of those inefficient loops we had before.
Thanks!


git-svn-id: file:///srv/svn/repos/haiku/haiku/trunk@22557 a95241bf-73f2-0310-859d-f6bbb57e9c96

headers/private/kernel/real_time_clock.h

@@ -1,5 +1,5 @@
 /*
- * Copyright 2006, Axel Dörfler, axeld@pinc-software.de. All rights reserved.
+ * Copyright 2006-2007, Axel Dörfler, axeld@pinc-software.de. All rights reserved.
  * Copyright 2003, Jeff Ward, jeff@r2d2.stcloudstate.edu. All rights reserved.
  *
  * Distributed under the terms of the MIT License.
@@ -13,7 +13,7 @@
 #include <time.h>
 
 
-#define RTC_EPOCHE_BASE_YEAR	1970
+#define RTC_EPOCH_BASE_YEAR	1970
 
 typedef struct rtc_info {
 	uint32	time;

src/system/kernel/arch/x86/arch_real_time_clock.c

@@ -1,5 +1,5 @@
 /*
- * Copyright 2005, Axel Dörfler, axeld@pinc-software.de
+ * Copyright 2005-2007, Axel Dörfler, axeld@pinc-software.de
  * Copyright 2003, Jeff Ward, jeff@r2d2.stcloudstate.edu. All rights reserved.
  *
  * Distributed under the terms of the MIT License.
@@ -141,7 +141,7 @@ cmos_to_secs(const cmos_time *cmos)
 {
 	struct tm t;
 	t.tm_year = bcd_to_int(cmos->century) * 100 + bcd_to_int(cmos->year)
-		- RTC_EPOCHE_BASE_YEAR;
+		- RTC_EPOCH_BASE_YEAR;
 	t.tm_mon = bcd_to_int(cmos->month) - 1;
 	t.tm_mday = bcd_to_int(cmos->day);
 	t.tm_hour = bcd_to_int(cmos->hour);
@@ -160,7 +160,7 @@ secs_to_cmos(uint32 seconds, cmos_time *cmos)
 	struct tm t;
 	rtc_secs_to_tm(seconds, &t);
 
-	wholeYear = t.tm_year + RTC_EPOCHE_BASE_YEAR;
+	wholeYear = t.tm_year + RTC_EPOCH_BASE_YEAR;
 
 	cmos->century = int_to_bcd(wholeYear / 100);
 	cmos->year = int_to_bcd(wholeYear % 100);

src/system/kernel/real_time_clock.c

@@ -23,6 +23,10 @@
 #endif
 
 
+#define RTC_SECONDS_DAY 86400
+#define RTC_EPOCH_JULIAN_DAY 2440588
+	// January 1st, 1970
+
 static struct real_time_data *sRealTimeData;
 static bool sIsGMT = false;
 static char sTimezoneFilename[B_PATH_NAME_LENGTH] = "";
@@ -161,130 +165,58 @@ get_rtc_info(rtc_info *info)
 // #pragma mark -
 
 
-#define SECONDS_31 2678400
+/*!	Converts the \a tm data to seconds. Note that the base year is not
-#define SECONDS_30 2592000
+	1900 as in POSIX, but 1970.
-#define SECONDS_28 2419200
+*/
-#define SECONDS_DAY 86400
-
-static uint32 sSecsPerMonth[12] = {SECONDS_31, SECONDS_28, SECONDS_31, SECONDS_30, 
-	SECONDS_31, SECONDS_30, SECONDS_31, SECONDS_31, SECONDS_30, SECONDS_31, SECONDS_30,
-	SECONDS_31};
-
-
-static bool
-leap_year(uint32 year)
-{
-	if (year % 400 == 0)
-		return true;
-
-	if (year % 100 == 0)
-		return false;
-
-	if (year % 4 == 0)
-		return true;
-
-	return false;
-}
-
-
-static inline uint32
-secs_this_year(uint32 year)
-{
-	if (leap_year(year))
-		return 31622400;
-
-	return 31536000;
-}
-
-
 uint32
-rtc_tm_to_secs(const struct tm *t)
+rtc_tm_to_secs(const struct tm *tm)
 {
-	uint32 wholeYear;
+	uint32 days;
-	uint32 time = 0;
+	int year, month;
-	uint32 i;
 
-	wholeYear = RTC_EPOCHE_BASE_YEAR + t->tm_year;
+	month = tm->tm_mon + 1;
+	year = tm->tm_year + RTC_EPOCH_BASE_YEAR;
 
-	// ToDo: get rid of these loops and compute the correct value
+	// Reference: Fliegel, H. F. and van Flandern, T. C. (1968).
-	//	i.e. days = (long)(year > 0) + year*365 + --year/4 - year/100 + year/400;
+	// Communications of the ACM, Vol. 11, No. 10 (October, 1968).
-	//	let sSecsPerMonth[] have the values already added up
+	days = tm->tm_mday - 32075 - RTC_EPOCH_JULIAN_DAY
+		+ 1461 * (year + 4800 + (month - 14) / 12) / 4
+		+ 367 * (month - 2 - 12 * ((month - 14) / 12)) / 12
+		- 3 * ((year + 4900 + (month - 14) / 12) / 100) / 4;
 
-	// Add up the seconds from all years since 1970 that have elapsed.
+	return days * RTC_SECONDS_DAY + tm->tm_hour * 3600 + tm->tm_min * 60
-	for (i = RTC_EPOCHE_BASE_YEAR; i < wholeYear; ++i) {
+		+ tm->tm_sec;
-		time += secs_this_year(i);
-	}
-
-	// Add up the seconds from all months passed this year.
-	for (i = 0; i < t->tm_mon && i < 12; ++i)
-		time += sSecsPerMonth[i];
-
-	// Add up the seconds from all days passed this month.
-	if (leap_year(wholeYear) && t->tm_mon >= 2)
-		time += SECONDS_DAY;
-
-	time += (t->tm_mday - 1) * SECONDS_DAY;
-	time += t->tm_hour * 3600;
-	time += t->tm_min * 60;
-	time += t->tm_sec;
-
-	return time;
 }
 
 
 void
 rtc_secs_to_tm(uint32 seconds, struct tm *t)
 {
-	uint32 wholeYear = RTC_EPOCHE_BASE_YEAR;
+	uint32 year, month, day, l, n;
-	uint32 secsThisYear;
-	bool keepLooping;
-	bool isLeapYear;
-	int temp;
-	int month;
 
-	keepLooping = 1;
+	// Reference: Fliegel, H. F. and van Flandern, T. C. (1968).
+	// Communications of the ACM, Vol. 11, No. 10 (October, 1968).
+	l = seconds / 86400 + 68569 + RTC_EPOCH_JULIAN_DAY;
+	n = 4 * l / 146097;
+	l = l - (146097 * n + 3) / 4;
+	year = 4000 * (l + 1) / 1461001;
+	l = l - 1461 * year / 4 + 31;
+	month = 80 * l / 2447;
+	day = l - 2447 * month / 80;
+	l = month / 11;
+	month = month + 2 - 12 * l;
+	year = 100 * (n - 49) + year + l;
 
-	// Determine the current year by starting at 1970 and incrementing whole_year as long as
+	t->tm_mday = day;
-	// we can keep subtracting secs_this_year from seconds.
+	t->tm_mon = month - 1;
-	while (keepLooping) {
+	t->tm_year = year - RTC_EPOCH_BASE_YEAR;
-		secsThisYear = secs_this_year(wholeYear);
-
-		if (seconds >= secsThisYear) {
-			seconds -= secsThisYear;
-			++wholeYear;
-		} else
-			keepLooping = false;
-	}
-
-	t->tm_year = wholeYear - RTC_EPOCHE_BASE_YEAR;
-
-	// Determine the current month
-	month = 0;
-	isLeapYear = leap_year(wholeYear);
-	do {
-		temp = seconds - sSecsPerMonth[month];
-
-		if (isLeapYear && month == 1)
-			temp -= SECONDS_DAY;
-
-		if (temp >= 0) {
-			seconds = temp;
-			++month;
-		}
-	} while (temp >= 0 && month < 12);
-
-	t->tm_mon = month;
-
-	t->tm_mday = seconds / SECONDS_DAY + 1;
-	seconds = seconds % SECONDS_DAY;
 
+	seconds = seconds % RTC_SECONDS_DAY;
 	t->tm_hour = seconds / 3600;
+ 
 	seconds = seconds % 3600;
-
 	t->tm_min = seconds / 60;
-	seconds = seconds % 60;
+	t->tm_sec = seconds % 60;
-
-	t->tm_sec = seconds;
 }