doc: Add gmtime_r() to rule A.5 exceptions

doc/contribute/coding_guidelines/index.rst

@@ -1456,6 +1456,7 @@ Zephyr codebase:
    :header: Function,Source
    :widths: auto
 
+   `gmtime_r()`_,POSIX.1-2001
    `strnlen()`_,POSIX.1-2008
    `strtok_r()`_,POSIX.1-2001
 
@@ -1482,5 +1483,6 @@ these functions can lead to compatibility issues with the third-party
 toolchains that come with their own C standard libraries.
 
 .. _main Zephyr repository: https://github.com/zephyrproject-rtos/zephyr
+.. _gmtime_r(): https://pubs.opengroup.org/onlinepubs/9699919799/functions/gmtime_r.html
 .. _strnlen(): https://pubs.opengroup.org/onlinepubs/9699919799/functions/strlen.html
 .. _strtok_r(): https://pubs.opengroup.org/onlinepubs/9699919799/functions/strtok.html

lib/libc/common/CMakeLists.txt

@@ -5,6 +5,7 @@ zephyr_system_include_directories(include)
 zephyr_library()
 zephyr_library_property(ALLOW_EMPTY TRUE)
 zephyr_library_sources_ifdef(CONFIG_COMMON_LIBC_ABORT source/stdlib/abort.c)
+zephyr_library_sources_ifdef(CONFIG_COMMON_LIBC_GMTIME_R source/time/gmtime_r.c)
 zephyr_library_sources_ifdef(CONFIG_COMMON_LIBC_TIME source/time/time.c)
 zephyr_library_sources_ifdef(CONFIG_COMMON_LIBC_MALLOC source/stdlib/malloc.c)
 zephyr_library_sources_ifdef(CONFIG_COMMON_LIBC_STRNLEN source/string/strnlen.c)

lib/libc/common/Kconfig

@@ -6,6 +6,11 @@ config COMMON_LIBC_ABORT
 	help
 	  common implementation of abort().
 
+config COMMON_LIBC_GMTIME_R
+	bool
+	help
+	  common implementation of gmtime_r().
+
 config COMMON_LIBC_TIME
 	bool
 	help

lib/libc/common/source/time/gmtime_r.c

@@ -0,0 +1,97 @@
+/*
+ * Copyright (c) 2019 Peter Bigot Consulting, LLC
+ *
+ * SPDX-License-Identifier: Apache-2.0
+ */
+
+/*
+ * The time_civil_from_days function is derived directly from public
+ * domain content written by Howard Hinnant and available at:
+ * http://howardhinnant.github.io/date_algorithms.html#civil_from_days
+ */
+
+#include <time.h>
+
+/* A signed type with the representation of time_t without its
+ * implications.
+ */
+typedef time_t bigint_type;
+
+/** Convert a UNIX time to civil time.
+ *
+ * This converts integral seconds since (before) 1970-01-01T00:00:00
+ * to the POSIX standard civil time representation.  Any adjustments
+ * due to time zone, leap seconds, or a different epoch must be
+ * applied to @p time before invoking this function.
+ *
+ * @param time the time represented as seconds.
+ *
+ * @return the time information for corresponding to the provided
+ * instant.
+ *
+ * @see http://howardhinnant.github.io/date_algorithms.html#civil_from_days
+ */
+static void time_civil_from_days(bigint_type z,
+				 struct tm *ZRESTRICT tp)
+{
+	tp->tm_wday = (z >= -4) ? ((z + 4) % 7) : ((z + 5) % 7 + 6);
+	z += 719468;
+
+	bigint_type era = ((z >= 0) ? z : (z - 146096)) / 146097;
+	unsigned int doe = (z - era * (bigint_type)146097);
+	unsigned int yoe = (doe - doe / 1460U + doe / 36524U - doe / 146096U)
+		/ 365U;
+	bigint_type y = (time_t)yoe + era * 400;
+	unsigned int doy = doe - (365U * yoe + yoe / 4U - yoe / 100U);
+	unsigned int mp = (5U * doy + 2U) / 153U;
+	unsigned int d = doy - (153U * mp + 2U) / 5U + 1U;
+	unsigned int m = mp + ((mp < 10) ? 3 : -9);
+
+	tp->tm_year = y + (m <= 2) - 1900;
+	tp->tm_mon = m - 1;
+	tp->tm_mday = d;
+
+	/* Everything above is explained on the referenced page, but
+	 * doy is relative to --03-01 and we need it relative to
+	 * --01-01.
+	 *
+	 * doy=306 corresponds to --01-01, doy=364 to --02-28, and
+	 * doy=365 to --02-29.  So we can just subtract 306 to handle
+	 * January and February.
+	 *
+	 * For doy<306 we have to add the number of days before
+	 * --03-01, which is 59 in a common year and 60 in a leap
+	 * year.  Note that the first year in the era is a leap year.
+	 */
+	if (doy >= 306U) {
+		tp->tm_yday = doy - 306U;
+	} else {
+		tp->tm_yday = doy + 59U + (((yoe % 4U == 0U) && (yoe % 100U != 0U)) || (yoe == 0U));
+	}
+}
+
+/* Convert a UNIX time to civil time.
+ *
+ * This converts integral seconds since (before) 1970-01-01T00:00:00
+ * to the POSIX standard civil time representation.  Any adjustments
+ * due to time zone, leap seconds, or a different epoch must be
+ * applied to @p time before invoking this function.
+ */
+struct tm *gmtime_r(const time_t *ZRESTRICT timep,
+		    struct tm *ZRESTRICT result)
+{
+	time_t z = *timep;
+	bigint_type days = (z >= 0 ? z : z - 86399) / 86400;
+	unsigned int rem = z - days * 86400;
+
+	*result = (struct tm){ 0 };
+
+	time_civil_from_days(days, result);
+
+	result->tm_hour = rem / 60U / 60U;
+	rem -= result->tm_hour * 60 * 60;
+	result->tm_min = rem / 60;
+	result->tm_sec = rem - result->tm_min * 60;
+
+	return result;
+}

lib/libc/minimal/Kconfig

@@ -79,6 +79,7 @@ config MINIMAL_LIBC_RAND
 config MINIMAL_LIBC_TIME
 	bool "Time functions"
 	select COMMON_LIBC_TIME if POSIX_CLOCK
+	select COMMON_LIBC_GMTIME_R
 	default y
 	help
 	  Enable time() and gmtime_r() for the minimal libc.

lib/libc/minimal/source/time/gmtime.c

@@ -4,99 +4,9 @@
  * SPDX-License-Identifier: Apache-2.0
  */
 
-/*
- * The time_civil_from_days function is derived directly from public
- * domain content written by Howard Hinnant and available at:
- * http://howardhinnant.github.io/date_algorithms.html#civil_from_days
- */
-
 #include <time.h>
 #include <zephyr/sys/libc-hooks.h>
 
-/* A signed type with the representation of time_t without its
- * implications.
- */
-typedef time_t bigint_type;
-
-/** Convert a UNIX time to civil time.
- *
- * This converts integral seconds since (before) 1970-01-01T00:00:00
- * to the POSIX standard civil time representation.  Any adjustments
- * due to time zone, leap seconds, or a different epoch must be
- * applied to @p time before invoking this function.
- *
- * @param time the time represented as seconds.
- *
- * @return the time information for corresponding to the provided
- * instant.
- *
- * @see http://howardhinnant.github.io/date_algorithms.html#civil_from_days
- */
-static void time_civil_from_days(bigint_type z,
-				 struct tm *ZRESTRICT tp)
-{
-	tp->tm_wday = (z >= -4) ? ((z + 4) % 7) : ((z + 5) % 7 + 6);
-	z += 719468;
-
-	bigint_type era = ((z >= 0) ? z : (z - 146096)) / 146097;
-	unsigned int doe = (z - era * (bigint_type)146097);
-	unsigned int yoe = (doe - doe / 1460U + doe / 36524U - doe / 146096U)
-		/ 365U;
-	bigint_type y = (time_t)yoe + era * 400;
-	unsigned int doy = doe - (365U * yoe + yoe / 4U - yoe / 100U);
-	unsigned int mp = (5U * doy + 2U) / 153U;
-	unsigned int d = doy - (153U * mp + 2U) / 5U + 1U;
-	unsigned int m = mp + ((mp < 10) ? 3 : -9);
-
-	tp->tm_year = y + (m <= 2) - 1900;
-	tp->tm_mon = m - 1;
-	tp->tm_mday = d;
-
-	/* Everything above is explained on the referenced page, but
-	 * doy is relative to --03-01 and we need it relative to
-	 * --01-01.
-	 *
-	 * doy=306 corresponds to --01-01, doy=364 to --02-28, and
-	 * doy=365 to --02-29.  So we can just subtract 306 to handle
-	 * January and February.
-	 *
-	 * For doy<306 we have to add the number of days before
-	 * --03-01, which is 59 in a common year and 60 in a leap
-	 * year.  Note that the first year in the era is a leap year.
-	 */
-	if (doy >= 306U) {
-		tp->tm_yday = doy - 306U;
-	} else {
-		tp->tm_yday = doy + 59U + (((yoe % 4U == 0U) && (yoe % 100U != 0U)) || (yoe == 0U));
-	}
-}
-
-/* Convert a UNIX time to civil time.
- *
- * This converts integral seconds since (before) 1970-01-01T00:00:00
- * to the POSIX standard civil time representation.  Any adjustments
- * due to time zone, leap seconds, or a different epoch must be
- * applied to @p time before invoking this function.
- */
-struct tm *gmtime_r(const time_t *ZRESTRICT timep,
-		    struct tm *ZRESTRICT result)
-{
-	time_t z = *timep;
-	bigint_type days = (z >= 0 ? z : z - 86399) / 86400;
-	unsigned int rem = z - days * 86400;
-
-	*result = (struct tm){ 0 };
-
-	time_civil_from_days(days, result);
-
-	result->tm_hour = rem / 60U / 60U;
-	rem -= result->tm_hour * 60 * 60;
-	result->tm_min = rem / 60;
-	result->tm_sec = rem - result->tm_min * 60;
-
-	return result;
-}
-
 #ifdef CONFIG_MINIMAL_LIBC_NON_REENTRANT_FUNCTIONS
 static Z_LIBC_DATA struct tm gmtime_result;