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The current implementation of 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 3x 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 for it which checks every day in a 160,000 years interval centered at 1970-01-01 against the expected result. [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> Signed-off-by: Thomas Gleixner <tglx@linutronix.de> Link: https://lore.kernel.org/r/20210622213616.313046-1-cassio.neri@gmail.com
99 lines
2.0 KiB
C
99 lines
2.0 KiB
C
// SPDX-License-Identifier: LGPL-2.1+
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#include <kunit/test.h>
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#include <linux/time.h>
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/*
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* Traditional implementation of leap year evaluation.
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*/
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static bool is_leap(long year)
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{
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return year % 4 == 0 && (year % 100 != 0 || year % 400 == 0);
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}
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/*
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* Gets the last day of a month.
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*/
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static int last_day_of_month(long year, int month)
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{
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if (month == 2)
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return 28 + is_leap(year);
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if (month == 4 || month == 6 || month == 9 || month == 11)
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return 30;
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return 31;
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}
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/*
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* Advances a date by one day.
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*/
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static void advance_date(long *year, int *month, int *mday, int *yday)
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{
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if (*mday != last_day_of_month(*year, *month)) {
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++*mday;
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++*yday;
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return;
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}
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*mday = 1;
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if (*month != 12) {
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++*month;
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++*yday;
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return;
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}
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*month = 1;
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*yday = 0;
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++*year;
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}
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/*
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* Checks every day in a 160000 years interval centered at 1970-01-01
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* against the expected result.
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*/
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static void time64_to_tm_test_date_range(struct kunit *test)
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{
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/*
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* 80000 years = (80000 / 400) * 400 years
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* = (80000 / 400) * 146097 days
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* = (80000 / 400) * 146097 * 86400 seconds
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*/
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time64_t total_secs = ((time64_t) 80000) / 400 * 146097 * 86400;
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long year = 1970 - 80000;
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int month = 1;
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int mdday = 1;
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int yday = 0;
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struct tm result;
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time64_t secs;
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s64 days;
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for (secs = -total_secs; secs <= total_secs; secs += 86400) {
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time64_to_tm(secs, 0, &result);
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days = div_s64(secs, 86400);
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#define FAIL_MSG "%05ld/%02d/%02d (%2d) : %ld", \
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year, month, mdday, yday, days
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KUNIT_ASSERT_EQ_MSG(test, year - 1900, result.tm_year, FAIL_MSG);
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KUNIT_ASSERT_EQ_MSG(test, month - 1, result.tm_mon, FAIL_MSG);
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KUNIT_ASSERT_EQ_MSG(test, mdday, result.tm_mday, FAIL_MSG);
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KUNIT_ASSERT_EQ_MSG(test, yday, result.tm_yday, FAIL_MSG);
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advance_date(&year, &month, &mdday, &yday);
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}
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}
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static struct kunit_case time_test_cases[] = {
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KUNIT_CASE(time64_to_tm_test_date_range),
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{}
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};
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static struct kunit_suite time_test_suite = {
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.name = "time_test_cases",
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.test_cases = time_test_cases,
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};
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kunit_test_suite(time_test_suite);
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