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diff --git a/src/usr.sbin/rdate/ntpleaps.h b/src/usr.sbin/rdate/ntpleaps.h
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+/*	$OpenBSD: ntpleaps.h,v 1.4 2007/11/25 16:40:04 jmc Exp $	*/
+
+/*
+ * Copyright (c) 2002 Thorsten Glaser. All rights reserved.
+ *
+ * Redistribution and use in source and binary forms, with or without
+ * modification, are permitted provided that the following conditions
+ * are met:
+ *
+ *    - Redistributions of source code must retain the above copyright
+ *      notice, this list of conditions and the following disclaimer.
+ *    - Redistributions in binary form must reproduce the above
+ *      copyright notice, this list of conditions and the following
+ *      disclaimer in the documentation and/or other materials provided
+ *      with the distribution.
+ *
+ * THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS
+ * "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT
+ * LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS
+ * FOR A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE
+ * COPYRIGHT HOLDERS OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT,
+ * INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING,
+ * BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES;
+ * LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER
+ * CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
+ * LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN
+ * ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE
+ * POSSIBILITY OF SUCH DAMAGE.
+ *
+ */
+
+/* Leap second support for SNTP clients
+ * This header file and its corresponding C file provide generic
+ * ability for NTP or SNTP clients to correctly handle leap seconds
+ * by reading them from an always existing file and subtracting the
+ * leap seconds from the NTP return value before setting the posix
+ * clock. This is fairly portable between operating systems and may
+ * be used for patching other ntp clients, too. The tzfile used is:
+ * /usr/share/zoneinfo/right/UTC which is available on any unix-like
+ * platform with the Olson tz library, which is necessary to get real
+ * leap second zoneinfo files and userland support anyways.
+ */
+
+#ifndef _NTPLEAPS_H
+#define _NTPLEAPS_H
+
+/* Offset between struct timeval.tv_sec and a tai64_t */
+#define	NTPLEAPS_OFFSET	(4611686018427387914ULL)
+
+/* Hide this ugly value from programmes */
+#define	SEC_TO_TAI64(s)	(NTPLEAPS_OFFSET + (u_int64_t)(s))
+#define	TAI64_TO_SEC(t)	((t) - NTPLEAPS_OFFSET)
+
+/* Initializes the leap second table. Does not need to be called
+ * before usage of the subtract function, but calls ntpleaps_read.
+ * returns 0 on success, -1 on error (displays a warning on stderr)
+ */
+int ntpleaps_init(void);
+
+/* Re-reads the leap second table, thus consuming quite much time.
+ * Ought to be called from within daemons at least once a month to
+ * ensure the in-memory table is always up-to-date.
+ * returns 0 on success, -1 on error (leap seconds will not be available)
+ */
+int ntpleaps_read(void);
+
+/* Subtracts leap seconds from the given value (converts NTP time
+ * to posix clock tick time.
+ * returns 0 on success, -1 on error (time is unchanged), 1 on leap second
+ */
+int ntpleaps_sub(u_int64_t *);
+
+#endif