git: 4285e024baa8 - main - strptime: Fix day-of-week calculation.
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Date: Mon, 09 Dec 2024 12:38:39 UTC
The branch main has been updated by des:
URL: https://cgit.FreeBSD.org/src/commit/?id=4285e024baa80f81d13cdcc016fdf0721fe57862
commit 4285e024baa80f81d13cdcc016fdf0721fe57862
Author: Dag-Erling Smørgrav <des@FreeBSD.org>
AuthorDate: 2024-12-09 12:37:45 +0000
Commit: Dag-Erling Smørgrav <des@FreeBSD.org>
CommitDate: 2024-12-09 12:38:22 +0000
strptime: Fix day-of-week calculation.
The day-of-week calculation used the raw year value without adjusting
for TM_YEAR_BASE, so it was off by one for 300 years out of every 400;
it just happened to be correct for 1901 through 2000. It also used a
loop where a simple addition would have sufficed.
While here, simplify our version of Gauss's algorithm, and document
that we assume the Gregorian calendar.
MFC after: 1 week
PR: 282916
Reviewed by: imp, allanjude, philip
Differential Revision: https://reviews.freebsd.org/D47977
---
etc/mtree/BSD.tests.dist | 2 ++
lib/libc/stdtime/strptime.3 | 7 ++++-
lib/libc/stdtime/strptime.c | 22 ++++++---------
lib/libc/tests/Makefile | 1 +
lib/libc/tests/stdtime/Makefile | 7 +++++
lib/libc/tests/stdtime/strptime_test.c | 50 ++++++++++++++++++++++++++++++++++
6 files changed, 74 insertions(+), 15 deletions(-)
diff --git a/etc/mtree/BSD.tests.dist b/etc/mtree/BSD.tests.dist
index 1762bbfb7bdc..e0c16bd5e570 100644
--- a/etc/mtree/BSD.tests.dist
+++ b/etc/mtree/BSD.tests.dist
@@ -382,6 +382,8 @@
..
stdlib
..
+ stdtime
+ ..
string
..
sys
diff --git a/lib/libc/stdtime/strptime.3 b/lib/libc/stdtime/strptime.3
index 0dfa33aa29cb..7df73d2d080a 100644
--- a/lib/libc/stdtime/strptime.3
+++ b/lib/libc/stdtime/strptime.3
@@ -23,7 +23,7 @@
.\" (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE OF
.\" THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
.\" "
-.Dd October 2, 2014
+.Dd December 9, 2024
.Dt STRPTIME 3
.Os
.Sh NAME
@@ -135,6 +135,11 @@ function has been contributed by Powerdog Industries.
.Pp
This man page was written by
.An J\(:org Wunsch .
+.Sh CAVEATS
+The
+.Fn strptime
+function assumes the Gregorian calendar and will produce incorrect
+results for dates prior to its introduction.
.Sh BUGS
Both the
.Fa %e
diff --git a/lib/libc/stdtime/strptime.c b/lib/libc/stdtime/strptime.c
index c988d968d580..5f1293c7a267 100644
--- a/lib/libc/stdtime/strptime.c
+++ b/lib/libc/stdtime/strptime.c
@@ -62,17 +62,16 @@ static char * _strptime(const char *, const char *, struct tm *, int *, locale_t
#define FLAG_WDAY (1 << 5)
/*
- * Calculate the week day of the first day of a year. Valid for
- * the Gregorian calendar, which began Sept 14, 1752 in the UK
- * and its colonies. Ref:
- * http://en.wikipedia.org/wiki/Determination_of_the_day_of_the_week
+ * Gauss's algorithm for the day of the week of the first day of any year
+ * in the Gregorian calendar.
*/
-
static int
first_wday_of(int year)
{
- return (((2 * (3 - (year / 100) % 4)) + (year % 100) +
- ((year % 100) / 4) + (isleap(year) ? 6 : 0) + 1) % 7);
+ return ((1 +
+ 5 * ((year - 1) % 4) +
+ 4 * ((year - 1) % 100) +
+ 6 * ((year - 1) % 400)) % 7);
}
static char *
@@ -674,13 +673,8 @@ label:
flags |= FLAG_MDAY;
}
if (!(flags & FLAG_WDAY)) {
- i = 0;
- wday_offset = first_wday_of(tm->tm_year);
- while (i++ <= tm->tm_yday) {
- if (wday_offset++ >= 6)
- wday_offset = 0;
- }
- tm->tm_wday = wday_offset;
+ wday_offset = first_wday_of(tm->tm_year + TM_YEAR_BASE);
+ tm->tm_wday = (wday_offset + tm->tm_yday) % 7;
flags |= FLAG_WDAY;
}
}
diff --git a/lib/libc/tests/Makefile b/lib/libc/tests/Makefile
index 76a79a9f578b..975c895770ee 100644
--- a/lib/libc/tests/Makefile
+++ b/lib/libc/tests/Makefile
@@ -16,6 +16,7 @@ TESTS_SUBDIRS+= secure
TESTS_SUBDIRS+= setjmp
TESTS_SUBDIRS+= stdio
TESTS_SUBDIRS+= stdlib
+TESTS_SUBDIRS+= stdtime
TESTS_SUBDIRS+= string
TESTS_SUBDIRS+= sys
TESTS_SUBDIRS+= termios
diff --git a/lib/libc/tests/stdtime/Makefile b/lib/libc/tests/stdtime/Makefile
new file mode 100644
index 000000000000..c7a7f5b9436f
--- /dev/null
+++ b/lib/libc/tests/stdtime/Makefile
@@ -0,0 +1,7 @@
+.include <bsd.own.mk>
+
+ATF_TESTS_C+= strptime_test
+
+TESTSDIR:= ${TESTSBASE}/${RELDIR:C/libc\/tests/libc/}
+
+.include <bsd.test.mk>
diff --git a/lib/libc/tests/stdtime/strptime_test.c b/lib/libc/tests/stdtime/strptime_test.c
new file mode 100644
index 000000000000..79a97764999c
--- /dev/null
+++ b/lib/libc/tests/stdtime/strptime_test.c
@@ -0,0 +1,50 @@
+/*-
+ * Copyright (c) 2024 Dag-Erling Smørgrav
+ *
+ * SPDX-License-Identifier: BSD-2-Clause
+ */
+
+#include <time.h>
+
+#include <atf-c.h>
+
+ATF_TC_WITHOUT_HEAD(dayofweek);
+ATF_TC_BODY(dayofweek, tc)
+{
+ static const struct {
+ const char *str;
+ int wday;
+ } cases[] = {
+ { "1582-12-20", 1 },
+ { "1700-03-01", 1 },
+ { "1752-09-14", 4 },
+ { "1800-12-31", 3 },
+ { "1801-01-01", 4 },
+ { "1900-12-31", 1 },
+ { "1901-01-01", 2 },
+ { "2000-12-31", 0 },
+ { "2001-01-01", 1 },
+ { "2100-12-31", 5 },
+ { "2101-01-01", 6 },
+ { "2200-12-31", 3 },
+ { "2201-01-01", 4 },
+ { },
+ };
+ struct tm tm;
+
+ for (unsigned int i = 0; cases[i].str != NULL; i++) {
+ if (strptime(cases[i].str, "%Y-%m-%d", &tm) == NULL) {
+ atf_tc_fail_nonfatal("failed to parse %s",
+ cases[i].str);
+ } else if (tm.tm_wday != cases[i].wday) {
+ atf_tc_fail_nonfatal("expected %d for %s, got %d",
+ cases[i].wday, cases[i].str, tm.tm_wday);
+ }
+ }
+}
+
+ATF_TP_ADD_TCS(tp)
+{
+ ATF_TP_ADD_TC(tp, dayofweek);
+ return (atf_no_error());
+}