diff --git a/shared/timespec-util.h b/shared/timespec-util.h
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+++ b/shared/timespec-util.h
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+/*
+ * Copyright © 2014 - 2015 Collabora, Ltd.
+ *
+ * Permission is hereby granted, free of charge, to any person obtaining
+ * a copy of this software and associated documentation files (the
+ * "Software"), to deal in the Software without restriction, including
+ * without limitation the rights to use, copy, modify, merge, publish,
+ * distribute, sublicense, and/or sell copies of the Software, and to
+ * permit persons to whom the Software is furnished to do so, subject to
+ * the following conditions:
+ *
+ * The above copyright notice and this permission notice (including the
+ * next paragraph) shall be included in all copies or substantial
+ * portions of the Software.
+ *
+ * THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND,
+ * EXPRESS OR IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF
+ * MERCHANTABILITY, FITNESS FOR A PARTICULAR PURPOSE AND
+ * NONINFRINGEMENT.  IN NO EVENT SHALL THE AUTHORS OR COPYRIGHT HOLDERS
+ * BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER LIABILITY, WHETHER IN AN
+ * ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM, OUT OF OR IN
+ * CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE
+ * SOFTWARE.
+ */
+
+#ifndef TIMESPEC_UTIL_H
+#define TIMESPEC_UTIL_H
+
+#define NSEC_PER_SEC 1000000000
+
+/* Subtract timespecs
+ *
+ * \param r[out] result: a - b
+ * \param a[in] operand
+ * \param b[in] operand
+ */
+static inline void
+timespec_sub(struct timespec *r,
+	     const struct timespec *a, const struct timespec *b)
+{
+	r->tv_sec = a->tv_sec - b->tv_sec;
+	r->tv_nsec = a->tv_nsec - b->tv_nsec;
+	if (r->tv_nsec < 0) {
+		r->tv_sec--;
+		r->tv_nsec += NSEC_PER_SEC;
+	}
+}
+
+/* Convert timespec to nanoseconds
+ *
+ * \param a timespec
+ * \return nanoseconds
+ */
+static inline int64_t
+timespec_to_nsec(const struct timespec *a)
+{
+	return (int64_t)a->tv_sec * NSEC_PER_SEC + a->tv_nsec;
+}
+
+
+#endif /* TIMESPEC_UTIL_H */