1 files changed, 36 insertions, 0 deletions
diff --git a/manual/examples/timespec_subtract.c b/manual/examples/timespec_subtract.c
new file mode 100644
index 0000000000..380d173aab
--- /dev/null
+++ b/manual/examples/timespec_subtract.c
@@ -0,0 +1,36 @@
+/* struct timespec subtraction.
+   Copyright (C) 1991-2024 Free Software Foundation, Inc.
+
+   This program is free software; you can redistribute it and/or
+   modify it under the terms of the GNU General Public License
+   as published by the Free Software Foundation; either version 2
+   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 General Public License for more details.
+
+   You should have received a copy of the GNU General Public License
+   along with this program; if not, see <https://www.gnu.org/licenses/>.
+*/
+#include <stdckdint.h>
+#include <time.h>
+
+/* Put into *R the difference between X and Y.
+   Return true if overflow occurs, false otherwise.  */
+
+bool
+timespec_subtract (struct timespec *r,
+		   struct timespec x, struct timespec y)
+{
+  /* Compute nanoseconds, setting @var{borrow} to 1, 0, or -1
+     for propagation into seconds.  */
+  long int nsec_diff = x.tv_nsec - y.tv_nsec;
+  int borrow = (nsec_diff < 0) - ! (nsec_diff < 1000000000);
+  r->tv_nsec = nsec_diff + 1000000000 * borrow;
+
+  /* Compute seconds, returning true if this overflows.  */
+  bool v = ckd_sub (&r->tv_sec, x.tv_sec, y.tv_sec);
+  return v ^ ckd_sub (&r->tv_sec, r->tv_sec, borrow);
+}