timespec_getres: new module

* lib/time.in.h (timespec_getres): New decl.
* lib/timespec_getres.c, m4/timespec_getres.m4:
* modules/timespec_getres, modules/timespec_getres-tests:
* tests/test-timespec_getres.c:
New files.
* m4/time_h.m4 (gl_TIME_H_REQUIRE_DEFAULTS, gl_TIME_H_DEFAULTS):
* modules/time (time.h):
Support timespec_getres.

2 files changed, 51 insertions, 0 deletions

diff --git a/lib/time.in.h b/lib/time.in.h
index a73fe59cbb..383e9768ba 100644
--- a/lib/time.in.h
+++ b/lib/time.in.h
@@ -120,6 +120,17 @@ _GL_CXXALIAS_SYS (timespec_get, int, (struct timespec *ts, int base));
 _GL_CXXALIASWARN (timespec_get);
 # endif
 
+/* Set *TS to the current time resolution, and return BASE.
+   Upon failure, return 0.  */
+# if @GNULIB_TIMESPEC_GETRES@
+#  if ! @HAVE_TIMESPEC_GETRES@
+_GL_FUNCDECL_SYS (timespec_getres, int, (struct timespec *ts, int base)
+                                        _GL_ARG_NONNULL ((1)));
+#  endif
+_GL_CXXALIAS_SYS (timespec_getres, int, (struct timespec *ts, int base));
+_GL_CXXALIASWARN (timespec_getres);
+# endif
+
 /* Sleep for at least RQTP seconds unless interrupted,  If interrupted,
    return -1 and store the remaining time into RMTP.  See
    <https://pubs.opengroup.org/onlinepubs/9699919799/functions/nanosleep.html>.  */
diff --git a/lib/timespec_getres.c b/lib/timespec_getres.c
new file mode 100644
index 0000000000..6fad0ce2d0
--- /dev/null
+++ b/lib/timespec_getres.c
@@ -0,0 +1,40 @@
+/* Get resolution of a time base.
+   Copyright 2021 Free Software Foundation, Inc.
+
+   This file is free software: you can redistribute it and/or modify
+   it under the terms of the GNU Lesser General Public License as
+   published by the Free Software Foundation; either version 3 of the
+   License, or (at your option) any later version.
+
+   This file is distributed in the hope that it will be useful,
+   but WITHOUT ANY WARRANTY; without even the implied warranty of
+   MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+   GNU Lesser General Public License for more details.
+
+   You should have received a copy of the GNU Lesser General Public License
+   along with this program.  If not, see <https://www.gnu.org/licenses/>.  */
+
+#include <config.h>
+
+#include <time.h>
+
+#include "timespec.h"
+
+/* Set TS to resolution of time base BASE.
+   Return BASE if successful, 0 otherwise.  */
+int
+timespec_getres (struct timespec *ts, int base)
+{
+  if (base == TIME_UTC)
+    {
+#if defined CLOCK_REALTIME && HAVE_CLOCK_GETRES
+      clock_getres (CLOCK_REALTIME, ts);
+#else
+      long int res = gettime_res ();
+      ts->tv_sec = res / TIMESPEC_HZ;
+      ts->tv_nsec = res % TIMESPEC_HZ;
+#endif
+      return base;
+    }
+  return 0;
+}