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diff --git a/include/haproxy/ticks.h b/include/haproxy/ticks.h
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+/*
+ * include/haproxy/ticks.h
+ * Functions and macros for manipulation of expiration timers
+ *
+ * Copyright (C) 2000-2020 Willy Tarreau - w@1wt.eu
+ *
+ * This library 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, version 2.1
+ * exclusively.
+ *
+ * This library 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 library; if not, write to the Free Software
+ * Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA  02110-1301  USA
+ */
+
+/*
+ * Using a mix of milliseconds and timeval for internal timers is expensive and
+ * overkill, because we don't need such a precision to compute timeouts.
+ * So we're converting them to "ticks".
+ *
+ * A tick is a representation of a date relative to another one, and is
+ * measured in milliseconds. The natural usage is to represent an absolute date
+ * relative to the current date. Since it is not practical to update all values
+ * each time the current date changes, instead we use the absolute date rounded
+ * down to fit in a tick. We then have to compare a tick to the current date to
+ * know whether it is in the future or in the past. If a tick is below the
+ * current date, it is in the past. If it is above, it is in the future. The
+ * values will wrap so we can't compare that easily, instead we check the sign
+ * of the difference between a tick and the current date.
+ *
+ * Proceeding like this allows us to manipulate dates that are stored in
+ * scalars with enough precision and range. For this reason, we store ticks in
+ * 32-bit integers. This is enough to handle dates that are between 24.85 days
+ * in the past and as much in the future.
+ * 
+ * We must both support absolute dates (well in fact, dates relative to now+/-
+ * 24 days), and intervals (for timeouts). Both types need an "eternity" magic
+ * value. For optimal code generation, we'll use zero as the magic value
+ * indicating that an expiration timer or a timeout is not set. We have to
+ * check that we don't return this value when adding timeouts to <now>. If a
+ * computation returns 0, we must increase it to 1 (which will push the timeout
+ * 1 ms further). For this reason, timeouts must not be added by hand but via
+ * the dedicated tick_add() function.
+ */
+
+#ifndef _HAPROXY_TICKS_H
+#define _HAPROXY_TICKS_H
+
+#include <haproxy/api.h>
+
+#define TICK_ETERNITY   0
+
+/* right now, ticks are milliseconds. Both negative ms and negative ticks
+ * indicate eternity.
+ */
+#define MS_TO_TICKS(ms) (ms)
+#define TICKS_TO_MS(tk) (tk)
+
+/* currently updated and stored in time.c */
+extern THREAD_LOCAL unsigned int   now_ms;   /* internal date in milliseconds (may wrap) */
+extern volatile unsigned int global_now_ms;
+
+/* return 1 if tick is set, otherwise 0 */
+static inline int tick_isset(int expire)
+{
+	return expire != 0;
+}
+
+/* Add <timeout> to <now>, and return the resulting expiration date.
+ * <timeout> will not be checked for null values.
+ */
+static inline int tick_add(int now, int timeout)
+{
+	now += timeout;
+	if (unlikely(!now))
+		now++;    /* unfortunate value */
+	return now;
+}
+
+/* add <timeout> to <now> if it is set, otherwise set it to eternity.
+ * Return the resulting expiration date.
+ */
+static inline int tick_add_ifset(int now, int timeout)
+{
+	if (!timeout)
+		return TICK_ETERNITY;
+	return tick_add(now, timeout);
+}
+
+/* return 1 if timer <t1> is before <t2>, none of which can be infinite. */
+static inline int tick_is_lt(int t1, int t2)
+{
+	return (t1 - t2) < 0;
+}
+
+/* return 1 if timer <t1> is before or equal to <t2>, none of which can be infinite. */
+static inline int tick_is_le(int t1, int t2)
+{
+	return (t1 - t2) <= 0;
+}
+
+/* return 1 if timer <timer> is expired at date <now>, otherwise zero */
+static inline int tick_is_expired(int timer, int now)
+{
+	if (unlikely(!tick_isset(timer)))
+		return 0;
+	if (unlikely((timer - now) <= 0))
+		return 1;
+	return 0;
+}
+
+/* return the first one of the two timers, both of which may be infinite */
+static inline int tick_first(int t1, int t2)
+{
+	if (!tick_isset(t1))
+		return t2;
+	if (!tick_isset(t2))
+		return t1;
+	if ((t1 - t2) <= 0)
+		return t1;
+	else
+		return t2;
+}
+
+/* return the first one of the two timers, where only the first one may be infinite */
+static inline int tick_first_2nz(int t1, int t2)
+{
+	if (!tick_isset(t1))
+		return t2;
+	if ((t1 - t2) <= 0)
+		return t1;
+	else
+		return t2;
+}
+
+/* return the number of ticks remaining from <now> to <exp>, or zero if expired */
+static inline int tick_remain(int now, int exp)
+{
+	if (tick_is_expired(exp, now))
+		return 0;
+	return exp - now;
+}
+
+#endif /* _HAPROXY_TICKS_H */
+
+/*
+ * Local variables:
+ *  c-indent-level: 8
+ *  c-basic-offset: 8
+ * End:
+ */