util: add macros for maximum, minimum and clamp

If MAX/MIN are defined in system headers, undefine them first.

ntp_core.c

@@ -1404,8 +1404,7 @@ receive_packet(NTP_Packet *message, struct timeval *now, double now_err, NCR_Ins
                            &sample_time,
                            offset, delay, dispersion,
                            root_delay, root_dispersion,
-                           message->stratum > inst->min_stratum ?
-                             message->stratum : inst->min_stratum,
+                           MAX(message->stratum, inst->min_stratum),
                            (NTP_Leap) pkt_leap);
 
       SRC_SelectSource(inst->source);

util.h

@@ -148,4 +148,17 @@ extern int UTI_CheckDirPermissions(const char *path, mode_t perm, uid_t uid, gid
 /* Fill buffer with random bytes */
 extern void UTI_GetRandomBytes(void *buf, unsigned int len);
 
+/* Macros to get maximum and minimum of two values */
+#ifdef MAX
+#undef MAX
+#endif
+#define MAX(x, y) ((x) > (y) ? (x) : (y))
+#ifdef MIN
+#undef MIN
+#endif
+#define MIN(x, y) ((x) < (y) ? (x) : (y))
+
+/* Macro to clamp a value between two values */
+#define CLAMP(min, x, max) (MAX((min), MIN((x), (max))))
+
 #endif /* GOT_UTIL_H */