--- /dev/null
+// SPDX-License-Identifier: LGPL-2.1+
+
+#include <kunit/test.h>
+#include <linux/time.h>
+
+/*
+ * Traditional implementation of leap year evaluation.
+ */
+static bool is_leap(long year)
+{
+ return year % 4 == 0 && (year % 100 != 0 || year % 400 == 0);
+}
+
+/*
+ * Gets the last day of a month.
+ */
+static int last_day_of_month(long year, int month)
+{
+ if (month == 2)
+ return 28 + is_leap(year);
+ if (month == 4 || month == 6 || month == 9 || month == 11)
+ return 30;
+ return 31;
+}
+
+/*
+ * Advances a date by one day.
+ */
+static void advance_date(long *year, int *month, int *mday, int *yday)
+{
+ if (*mday != last_day_of_month(*year, *month)) {
+ ++*mday;
+ ++*yday;
+ return;
+ }
+
+ *mday = 1;
+ if (*month != 12) {
+ ++*month;
+ ++*yday;
+ return;
+ }
+
+ *month = 1;
+ *yday = 0;
+ ++*year;
+}
+
+/*
+ * Checks every day in a 160000 years interval centered at 1970-01-01
+ * against the expected result.
+ */
+static void time64_to_tm_test_date_range(struct kunit *test)
+{
+ /*
+ * 80000 years = (80000 / 400) * 400 years
+ * = (80000 / 400) * 146097 days
+ * = (80000 / 400) * 146097 * 86400 seconds
+ */
+ time64_t total_secs = ((time64_t) 80000) / 400 * 146097 * 86400;
+ long year = 1970 - 80000;
+ int month = 1;
+ int mdday = 1;
+ int yday = 0;
+
+ struct tm result;
+ time64_t secs;
+ s64 days;
+
+ for (secs = -total_secs; secs <= total_secs; secs += 86400) {
+
+ time64_to_tm(secs, 0, &result);
+
+ days = div_s64(secs, 86400);
+
+ #define FAIL_MSG "%05ld/%02d/%02d (%2d) : %ld", \
+ year, month, mdday, yday, days
+
+ KUNIT_ASSERT_EQ_MSG(test, year - 1900, result.tm_year, FAIL_MSG);
+ KUNIT_ASSERT_EQ_MSG(test, month - 1, result.tm_mon, FAIL_MSG);
+ KUNIT_ASSERT_EQ_MSG(test, mdday, result.tm_mday, FAIL_MSG);
+ KUNIT_ASSERT_EQ_MSG(test, yday, result.tm_yday, FAIL_MSG);
+
+ advance_date(&year, &month, &mdday, &yday);
+ }
+}
+
+static struct kunit_case time_test_cases[] = {
+ KUNIT_CASE(time64_to_tm_test_date_range),
+ {}
+};
+
+static struct kunit_suite time_test_suite = {
+ .name = "time_test_cases",
+ .test_cases = time_test_cases,
+};
+
+kunit_test_suite(time_test_suite);
/*
* Converts the calendar time to broken-down time representation
- * Based on code from glibc-2.6
*
* 2009-7-14:
* Moved from glibc-2.6 to kernel by Zhaolei<zhaolei@cn.fujitsu.com>
+ * 2021-06-02:
+ * Reimplemented by Cassio Neri <cassio.neri@gmail.com>
*/
#include <linux/time.h>
#include <linux/module.h>
-
-/*
- * Nonzero if YEAR is a leap year (every 4 years,
- * except every 100th isn't, and every 400th is).
- */
-static int __isleap(long year)
-{
- return (year) % 4 == 0 && ((year) % 100 != 0 || (year) % 400 == 0);
-}
-
-/* do a mathdiv for long type */
-static long math_div(long a, long b)
-{
- return a / b - (a % b < 0);
-}
-
-/* How many leap years between y1 and y2, y1 must less or equal to y2 */
-static long leaps_between(long y1, long y2)
-{
- long leaps1 = math_div(y1 - 1, 4) - math_div(y1 - 1, 100)
- + math_div(y1 - 1, 400);
- long leaps2 = math_div(y2 - 1, 4) - math_div(y2 - 1, 100)
- + math_div(y2 - 1, 400);
- return leaps2 - leaps1;
-}
-
-/* How many days come before each month (0-12). */
-static const unsigned short __mon_yday[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}
-};
+#include <linux/kernel.h>
#define SECS_PER_HOUR (60 * 60)
#define SECS_PER_DAY (SECS_PER_HOUR * 24)
*/
void time64_to_tm(time64_t totalsecs, int offset, struct tm *result)
{
- long days, rem, y;
+ u32 u32tmp, day_of_century, year_of_century, day_of_year, month, day;
+ u64 u64tmp, udays, century, year;
+ bool is_Jan_or_Feb, is_leap_year;
+ long days, rem;
int remainder;
- const unsigned short *ip;
days = div_s64_rem(totalsecs, SECS_PER_DAY, &remainder);
rem = remainder;
if (result->tm_wday < 0)
result->tm_wday += 7;
- y = 1970;
-
- while (days < 0 || days >= (__isleap(y) ? 366 : 365)) {
- /* Guess a corrected year, assuming 365 days per year. */
- long yg = y + math_div(days, 365);
-
- /* Adjust DAYS and Y to match the guessed year. */
- days -= (yg - y) * 365 + leaps_between(y, yg);
- y = yg;
- }
-
- result->tm_year = y - 1900;
-
- result->tm_yday = days;
-
- ip = __mon_yday[__isleap(y)];
- for (y = 11; days < ip[y]; y--)
- continue;
- days -= ip[y];
-
- result->tm_mon = y;
- result->tm_mday = days + 1;
+ /*
+ * The following algorithm is, basically, Proposition 6.3 of Neri
+ * and Schneider [1]. In a few words: it works on the computational
+ * (fictitious) calendar where the year starts in March, month = 2
+ * (*), and finishes in February, month = 13. This calendar is
+ * mathematically convenient because the day of the year does not
+ * depend on whether the year is leap or not. For instance:
+ *
+ * March 1st 0-th day of the year;
+ * ...
+ * April 1st 31-st day of the year;
+ * ...
+ * January 1st 306-th day of the year; (Important!)
+ * ...
+ * February 28th 364-th day of the year;
+ * February 29th 365-th day of the year (if it exists).
+ *
+ * After having worked out the date in the computational calendar
+ * (using just arithmetics) it's easy to convert it to the
+ * corresponding date in the Gregorian calendar.
+ *
+ * [1] "Euclidean Affine Functions and Applications to Calendar
+ * Algorithms". https://arxiv.org/abs/2102.06959
+ *
+ * (*) The numbering of months follows tm more closely and thus,
+ * is slightly different from [1].
+ */
+
+ udays = ((u64) days) + 2305843009213814918ULL;
+
+ u64tmp = 4 * udays + 3;
+ century = div64_u64_rem(u64tmp, 146097, &u64tmp);
+ day_of_century = (u32) (u64tmp / 4);
+
+ u32tmp = 4 * day_of_century + 3;
+ u64tmp = 2939745ULL * u32tmp;
+ year_of_century = upper_32_bits(u64tmp);
+ day_of_year = lower_32_bits(u64tmp) / 2939745 / 4;
+
+ year = 100 * century + year_of_century;
+ is_leap_year = year_of_century ? !(year_of_century % 4) : !(century % 4);
+
+ u32tmp = 2141 * day_of_year + 132377;
+ month = u32tmp >> 16;
+ day = ((u16) u32tmp) / 2141;
+
+ /*
+ * Recall that January 1st is the 306-th day of the year in the
+ * computational (not Gregorian) calendar.
+ */
+ is_Jan_or_Feb = day_of_year >= 306;
+
+ /* Convert to the Gregorian calendar and adjust to Unix time. */
+ year = year + is_Jan_or_Feb - 6313183731940000ULL;
+ month = is_Jan_or_Feb ? month - 12 : month;
+ day = day + 1;
+ day_of_year += is_Jan_or_Feb ? -306 : 31 + 28 + is_leap_year;
+
+ /* Convert to tm's format. */
+ result->tm_year = (long) (year - 1900);
+ result->tm_mon = (int) month;
+ result->tm_mday = (int) day;
+ result->tm_yday = (int) day_of_year;
}
EXPORT_SYMBOL(time64_to_tm);
projects / platform / kernel / linux-rpi.git / commitdiff