From 8c25372709d256d83858be454987137dc202b725 Mon Sep 17 00:00:00 2001
From: Paul Eggert <eggert@cs.ucla.edu>
Date: Mon, 18 Apr 2022 13:08:27 -0700
Subject: [PATCH 3/6] Add Gnulib gettime-res module

* admin/merge-gnulib (GNULIB_MODULES): Add gettime-res.
* lib/gettime-res.c: New file, copied from Gnulib.
* lib/gnulib.mk.in, m4/gnulib-comp.m4: Regenerate.
---
 admin/merge-gnulib |  3 +-
 lib/gettime-res.c  | 78 ++++++++++++++++++++++++++++++++++++++++++++++
 lib/gnulib.mk.in   |  9 ++++++
 m4/gnulib-comp.m4  |  3 ++
 4 files changed, 92 insertions(+), 1 deletion(-)
 create mode 100644 lib/gettime-res.c

diff --git a/admin/merge-gnulib b/admin/merge-gnulib
index ea3d23686f..0279d1f99d 100755
--- a/admin/merge-gnulib
+++ b/admin/merge-gnulib
@@ -37,7 +37,8 @@ GNULIB_MODULES=
   fchmodat fcntl fcntl-h fdopendir file-has-acl
   filemode filename filevercmp flexmember fpieee
   free-posix fstatat fsusage fsync futimens
-  getloadavg getopt-gnu getrandom gettime gettimeofday gitlog-to-changelog
+  getloadavg getopt-gnu getrandom
+  gettime gettime-res gettimeofday gitlog-to-changelog
   ieee754-h ignore-value intprops largefile libgmp lstat
   manywarnings memmem-simple mempcpy memrchr minmax mkostemp mktime
   nanosleep nproc nstrftime
diff --git a/lib/gettime-res.c b/lib/gettime-res.c
new file mode 100644
index 0000000000..611f83ad27
--- /dev/null
+++ b/lib/gettime-res.c
@@ -0,0 +1,78 @@
+/* Get the system clock resolution.
+
+   Copyright 2021-2022 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/>.  */
+
+/* Written by Paul Eggert.  */
+
+#include <config.h>
+
+#include "timespec.h"
+
+static long int _GL_ATTRIBUTE_CONST
+gcd (long int a, long int b)
+{
+  while (b != 0)
+    {
+      long int r = a % b;
+      a = b;
+      b = r;
+    }
+  return a;
+}
+
+/* Return the system time resolution in nanoseconds.  */
+
+long int
+gettime_res (void)
+{
+  struct timespec res;
+#if defined CLOCK_REALTIME && HAVE_CLOCK_GETRES
+  clock_getres (CLOCK_REALTIME, &res);
+#elif defined HAVE_TIMESPEC_GETRES
+  timespec_getres (&res, TIME_UTC);
+#else
+  /* Guess high and let the later code deduce better.  */
+  res.tv_sec = 1;
+  res.tv_nsec = 0;
+#endif
+
+  /* On all Gnulib platforms the following calculations do not overflow.  */
+
+  long int hz = TIMESPEC_HZ;
+  long int r = hz * res.tv_sec + res.tv_nsec;
+
+  /* On some platforms, clock_getres (CLOCK_REALTIME, ...) yields a
+     too-large resolution, under the mistaken theory that it should
+     return the timer interval.  For example, on AIX 7.2 POWER8
+     clock_getres yields 10 ms even though clock_gettime yields 1 µs
+     resolution.  Work around the problem with high probability by
+     trying clock_gettime several times and observing the resulting
+     bounds on resolution.  */
+  for (int i = 0; 1 < r && i < 32; i++)
+    {
+      struct timespec now = current_timespec ();
+      r = gcd (r, now.tv_nsec ? now.tv_nsec : hz);
+    }
+
+  return r;
+}
+
+/*
+ * Hey Emacs!
+ * Local Variables:
+ * coding: utf-8
+ * End:
+ */
diff --git a/lib/gnulib.mk.in b/lib/gnulib.mk.in
index bbb05fdba5..fbc199faaf 100644
--- a/lib/gnulib.mk.in
+++ b/lib/gnulib.mk.in
@@ -114,6 +114,7 @@
 #  getopt-gnu \
 #  getrandom \
 #  gettime \
+#  gettime-res \
 #  gettimeofday \
 #  gitlog-to-changelog \
 #  ieee754-h \
@@ -2188,6 +2189,14 @@ libgnu_a_SOURCES += gettime.c
 endif
 ## end   gnulib module gettime
 
+## begin gnulib module gettime-res
+ifeq (,$(OMIT_GNULIB_MODULE_gettime-res))
+
+libgnu_a_SOURCES += gettime-res.c
+
+endif
+## end   gnulib module gettime-res
+
 ## begin gnulib module gettimeofday
 ifeq (,$(OMIT_GNULIB_MODULE_gettimeofday))
 
diff --git a/m4/gnulib-comp.m4 b/m4/gnulib-comp.m4
index fb5f1b52a4..a04ec44be9 100644
--- a/m4/gnulib-comp.m4
+++ b/m4/gnulib-comp.m4
@@ -112,6 +112,7 @@ AC_DEFUN
   # Code from module getrandom:
   # Code from module gettext-h:
   # Code from module gettime:
+  # Code from module gettime-res:
   # Code from module gettimeofday:
   # Code from module gitlog-to-changelog:
   # Code from module group-member:
@@ -371,6 +372,7 @@ AC_DEFUN
                  [test $HAVE_GETRANDOM = 0 || test $REPLACE_GETRANDOM = 1])
   gl_SYS_RANDOM_MODULE_INDICATOR([getrandom])
   gl_GETTIME
+  gl_GETTIME_RES
   gl_FUNC_GETTIMEOFDAY
   gl_CONDITIONAL([GL_COND_OBJ_GETTIMEOFDAY],
                  [test $HAVE_GETTIMEOFDAY = 0 || test $REPLACE_GETTIMEOFDAY = 1])
@@ -1270,6 +1272,7 @@ AC_DEFUN
   lib/getopt_int.h
   lib/getrandom.c
   lib/gettext.h
+  lib/gettime-res.c
   lib/gettime.c
   lib/gettimeofday.c
   lib/gl_openssl.h
-- 
2.35.1