5.4-stable review patch. If anyone has any objections, please let me know.
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From: Cassio Neri cassio.neri@gmail.com
commit 1d1bb12a8b1805ddeef9793ebeb920179fb0fa38 upstream.
The current implementation of rtc_time64_to_tm() contains unnecessary loops, branches and look-up tables. The new one uses an arithmetic-based algorithm appeared in [1] and is approximately 4.3 times faster (YMMV).
The drawback is that the new code isn't intuitive and contains many 'magic numbers' (not unusual for this type of algorithm). However, [1] justifies all those numbers and, given this function's history, the code is unlikely to need much maintenance, if any at all.
Add a KUnit test case that checks every day in a 160,000 years interval starting on 1970-01-01 against the expected result. Add a new config RTC_LIB_KUNIT_TEST symbol to give the option to run this test suite.
[1] Neri, Schneider, "Euclidean Affine Functions and Applications to Calendar Algorithms". https://arxiv.org/abs/2102.06959
Signed-off-by: Cassio Neri cassio.neri@gmail.com Reported-by: kernel test robot lkp@intel.com Signed-off-by: Alexandre Belloni alexandre.belloni@bootlin.com Link: https://lore.kernel.org/r/20210624201343.85441-1-cassio.neri@gmail.com Signed-off-by: Uwe Kleine-König u.kleine-koenig@baylibre.com Signed-off-by: Greg Kroah-Hartman gregkh@linuxfoundation.org --- drivers/rtc/Kconfig | 10 ++++ drivers/rtc/Makefile | 1 drivers/rtc/lib.c | 107 ++++++++++++++++++++++++++++++++++++------------- drivers/rtc/lib_test.c | 79 ++++++++++++++++++++++++++++++++++++ 4 files changed, 170 insertions(+), 27 deletions(-) create mode 100644 drivers/rtc/lib_test.c
--- a/drivers/rtc/Kconfig +++ b/drivers/rtc/Kconfig @@ -10,6 +10,16 @@ config RTC_MC146818_LIB bool select RTC_LIB
+config RTC_LIB_KUNIT_TEST + tristate "KUnit test for RTC lib functions" if !KUNIT_ALL_TESTS + depends on KUNIT + default KUNIT_ALL_TESTS + select RTC_LIB + help + Enable this option to test RTC library functions. + + If unsure, say N. + menuconfig RTC_CLASS bool "Real Time Clock" default n --- a/drivers/rtc/Makefile +++ b/drivers/rtc/Makefile @@ -186,3 +186,4 @@ obj-$(CONFIG_RTC_DRV_WM8350) += rtc-wm83 obj-$(CONFIG_RTC_DRV_X1205) += rtc-x1205.o obj-$(CONFIG_RTC_DRV_XGENE) += rtc-xgene.o obj-$(CONFIG_RTC_DRV_ZYNQMP) += rtc-zynqmp.o +obj-$(CONFIG_RTC_LIB_KUNIT_TEST) += lib_test.o --- a/drivers/rtc/lib.c +++ b/drivers/rtc/lib.c @@ -6,6 +6,8 @@ * Author: Alessandro Zummo a.zummo@towertech.it * * based on arch/arm/common/rtctime.c and other bits + * + * Author: Cassio Neri cassio.neri@gmail.com (rtc_time64_to_tm) */
#include <linux/export.h> @@ -22,8 +24,6 @@ static const unsigned short rtc_ydays[2] { 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) - /* * The number of days in the month. */ @@ -42,42 +42,95 @@ int rtc_year_days(unsigned int day, unsi } EXPORT_SYMBOL(rtc_year_days);
-/* - * rtc_time64_to_tm - Converts time64_t to rtc_time. - * Convert seconds since 01-01-1970 00:00:00 to Gregorian date. +/** + * rtc_time64_to_tm - converts time64_t to rtc_time. + * + * @time: The number of seconds since 01-01-1970 00:00:00. + * (Must be positive.) + * @tm: Pointer to the struct rtc_time. */ void rtc_time64_to_tm(time64_t time, struct rtc_time *tm) { - unsigned int month, year, secs; + unsigned int secs; int days;
+ u64 u64tmp; + u32 u32tmp, udays, century, day_of_century, year_of_century, year, + day_of_year, month, day; + bool is_Jan_or_Feb, is_leap_year; + /* time must be positive */ days = div_s64_rem(time, 86400, &secs);
/* day of the week, 1970-01-01 was a Thursday */ tm->tm_wday = (days + 4) % 7;
- year = 1970 + days / 365; - days -= (year - 1970) * 365 - + LEAPS_THRU_END_OF(year - 1) - - LEAPS_THRU_END_OF(1970 - 1); - while (days < 0) { - year -= 1; - days += 365 + is_leap_year(year); - } - tm->tm_year = year - 1900; - tm->tm_yday = days + 1; - - for (month = 0; month < 11; month++) { - int newdays; - - newdays = days - rtc_month_days(month, year); - if (newdays < 0) - break; - days = newdays; - } - tm->tm_mon = month; - tm->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 rtc_time more closely and + * thus, is slightly different from [1]. + */ + + udays = ((u32) days) + 719468; + + u32tmp = 4 * udays + 3; + century = u32tmp / 146097; + day_of_century = u32tmp % 146097 / 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 != 0 ? + year_of_century % 4 == 0 : century % 4 == 0; + + u32tmp = 2141 * day_of_year + 132377; + month = u32tmp >> 16; + day = ((u16) u32tmp) / 2141; + + /* + * Recall that January 01 is the 306-th day of the year in the + * computational (not Gregorian) calendar. + */ + is_Jan_or_Feb = day_of_year >= 306; + + /* Converts to the Gregorian calendar. */ + year = year + is_Jan_or_Feb; + month = is_Jan_or_Feb ? month - 12 : month; + day = day + 1; + + day_of_year = is_Jan_or_Feb ? + day_of_year - 306 : day_of_year + 31 + 28 + is_leap_year; + + /* Converts to rtc_time's format. */ + tm->tm_year = (int) (year - 1900); + tm->tm_mon = (int) month; + tm->tm_mday = (int) day; + tm->tm_yday = (int) day_of_year + 1;
tm->tm_hour = secs / 3600; secs -= tm->tm_hour * 3600; --- /dev/null +++ b/drivers/rtc/lib_test.c @@ -0,0 +1,79 @@ +// SPDX-License-Identifier: LGPL-2.1+ + +#include <kunit/test.h> +#include <linux/rtc.h> + +/* + * Advance a date by one day. + */ +static void advance_date(int *year, int *month, int *mday, int *yday) +{ + if (*mday != rtc_month_days(*month - 1, *year)) { + ++*mday; + ++*yday; + return; + } + + *mday = 1; + if (*month != 12) { + ++*month; + ++*yday; + return; + } + + *month = 1; + *yday = 1; + ++*year; +} + +/* + * Checks every day in a 160000 years interval starting on 1970-01-01 + * against the expected result. + */ +static void rtc_time64_to_tm_test_date_range(struct kunit *test) +{ + /* + * 160000 years = (160000 / 400) * 400 years + * = (160000 / 400) * 146097 days + * = (160000 / 400) * 146097 * 86400 seconds + */ + time64_t total_secs = ((time64_t) 160000) / 400 * 146097 * 86400; + + int year = 1970; + int month = 1; + int mday = 1; + int yday = 1; + + struct rtc_time result; + time64_t secs; + s64 days; + + for (secs = 0; secs <= total_secs; secs += 86400) { + + rtc_time64_to_tm(secs, &result); + + days = div_s64(secs, 86400); + + #define FAIL_MSG "%d/%02d/%02d (%2d) : %ld", \ + year, month, mday, 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, mday, result.tm_mday, FAIL_MSG); + KUNIT_ASSERT_EQ_MSG(test, yday, result.tm_yday, FAIL_MSG); + + advance_date(&year, &month, &mday, &yday); + } +} + +static struct kunit_case rtc_lib_test_cases[] = { + KUNIT_CASE(rtc_time64_to_tm_test_date_range), + {} +}; + +static struct kunit_suite rtc_lib_test_suite = { + .name = "rtc_lib_test_cases", + .test_cases = rtc_lib_test_cases, +}; + +kunit_test_suite(rtc_lib_test_suite);