compat: add clock_getres for darwin

compat/clock_getres.c

@@ -0,0 +1,54 @@
+/*****************************************************************************
+ * clock_getres.c: POSIX clock_getres() replacement
+ *****************************************************************************
+ * Copyright © 2020 VLC authors and VideoLAN
+ *
+ * Author: Marvin Scholz <epirat07 at gmail dot com>
+ *
+ * This program 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 2.1 of the License, or
+ * (at your option) any later version.
+ *
+ * This program 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, write to the Free Software Foundation,
+ * Inc., 51 Franklin Street, Fifth Floor, Boston MA 02110-1301, USA.
+ *****************************************************************************/
+
+#ifdef __APPLE__
+
+#ifdef HAVE_CONFIG_H
+# include <config.h>
+#endif
+
+#include <sys/errno.h>
+#include <sys/types.h>
+#include <sys/time.h>
+#include <mach/clock_types.h>
+
+int clock_getres(clockid_t clock_id, struct timespec *tp)
+{
+    switch (clock_id) {
+        case CLOCK_MONOTONIC:
+        case CLOCK_REALTIME:
+            // For realtime, it is using gettimeofday and for
+            // the monotonic time it is relative to the system
+            // boot time. Both of these use timeval, which has
+            // at best microsecond precision.
+            tp->tv_sec = 0;
+            tp->tv_nsec = NSEC_PER_USEC;
+            break;
+        default:
+            errno = EINVAL;
+            return -1;
+    }
+
+    return 0;
+}
+
+#endif

configure.ac

@@ -930,7 +930,7 @@ AC_SUBST([LIBRT])
 
 dnl  Check for clock_* functions, needs to be done here,
 dnl  after the -lrt check
-AC_REPLACE_FUNCS([clock_gettime clock_nanosleep])
+AC_REPLACE_FUNCS([clock_gettime clock_nanosleep clock_getres])
 
 dnl
 dnl Check for headers

include/vlc_fixups.h

@@ -672,6 +672,9 @@ FILE *vlc_win32_tmpfile(void);
 # ifndef HAVE_CLOCK_GETTIME
 int clock_gettime(clockid_t clock_id, struct timespec *tp);
 # endif
+# ifndef HAVE_CLOCK_GETRES
+int clock_getres(clockid_t clock_id, struct timespec *tp);
+# endif
 # ifndef HAVE_CLOCK_NANOSLEEP
 int clock_nanosleep(clockid_t clock_id, int flags,
         const struct timespec *rqtp, struct timespec *rmtp);