timespec UPDATE reworked time functions

merged some time functions in order to be able to directly get some time in the future with a single function call
instead of having to get the current time and then add some time to it, also created a new function, which returns
the difference from the current time so that it can be put into condition statements instead of having to get the
current time and then get the difference.
diff --git a/src/session.c b/src/session.c
index e97ea7b..98e40b2 100644
--- a/src/session.c
+++ b/src/session.c
@@ -57,51 +57,29 @@
 extern struct nc_server_opts server_opts;
 
 int
-nc_gettimespec_mono(struct timespec *ts)
-{
-#ifdef CLOCK_MONOTONIC_RAW
-    return clock_gettime(CLOCK_MONOTONIC_RAW, ts);
-#elif defined (CLOCK_MONOTONIC)
-    return clock_gettime(CLOCK_MONOTONIC, ts);
-#else
-    /* no monotonic clock available, return realtime */
-    return nc_gettimespec_real(ts);
-#endif
-}
-
-int
-nc_gettimespec_real(struct timespec *ts)
+nc_gettimespec_real_add(struct timespec *ts, uint32_t msec)
 {
 #ifdef CLOCK_REALTIME
-    return clock_gettime(CLOCK_REALTIME, ts);
+    if (clock_gettime(CLOCK_REALTIME, ts)) {
+        return -1;
+    }
 #else
     int rc;
     struct timeval tv;
 
     rc = gettimeofday(&tv, NULL);
-    if (!rc) {
+    if (rc) {
+        return -1;
+    } else {
         ts->tv_sec = (time_t)tv.tv_sec;
         ts->tv_nsec = 1000L * (long)tv.tv_usec;
     }
-    return rc;
 #endif
-}
 
-/* ts1 < ts2 -> +, ts1 > ts2 -> -, returns milliseconds */
-int32_t
-nc_difftimespec(const struct timespec *ts1, const struct timespec *ts2)
-{
-    int64_t nsec_diff = 0;
+    if (!msec) {
+        return 0;
+    }
 
-    nsec_diff += (((int64_t)ts2->tv_sec) - ((int64_t)ts1->tv_sec)) * 1000000000L;
-    nsec_diff += ((int64_t)ts2->tv_nsec) - ((int64_t)ts1->tv_nsec);
-
-    return nsec_diff ? nsec_diff / 1000000L : 0;
-}
-
-void
-nc_addtimespec(struct timespec *ts, uint32_t msec)
-{
     assert((ts->tv_nsec >= 0) && (ts->tv_nsec < 1000000000L));
 
     ts->tv_sec += msec / 1000;
@@ -116,6 +94,60 @@
     }
 
     assert((ts->tv_nsec >= 0) && (ts->tv_nsec < 1000000000L));
+    return 0;
+}
+
+int
+nc_gettimespec_mono_add(struct timespec *ts, uint32_t msec)
+{
+    #ifdef CLOCK_MONOTONIC_RAW
+    if (clock_gettime(CLOCK_MONOTONIC_RAW, ts)) {
+        return -1;
+    }
+    #elif defined (CLOCK_MONOTONIC)
+    if (clock_gettime(CLOCK_MONOTONIC, ts)) {
+        return -1;
+    }
+    #else
+    /* no monotonic clock available, return realtime */
+    if (nc_gettimespec_real_add(ts, 0)) {
+        return -1;
+    }
+#endif
+
+    if (!msec) {
+        return 0;
+    }
+
+    assert((ts->tv_nsec >= 0) && (ts->tv_nsec < 1000000000L));
+
+    ts->tv_sec += msec / 1000;
+    ts->tv_nsec += (msec % 1000) * 1000000L;
+
+    if (ts->tv_nsec >= 1000000000L) {
+        ++ts->tv_sec;
+        ts->tv_nsec -= 1000000000L;
+    } else if (ts->tv_nsec < 0) {
+        --ts->tv_sec;
+        ts->tv_nsec += 1000000000L;
+    }
+
+    assert((ts->tv_nsec >= 0) && (ts->tv_nsec < 1000000000L));
+    return 0;
+}
+
+int32_t
+nc_difftimespec_cur(const struct timespec *ts)
+{
+    struct timespec cur;
+    int64_t nsec_diff = 0;
+
+    nc_gettimespec_mono_add(&cur, 0);
+
+    nsec_diff += (((int64_t)ts->tv_sec) - ((int64_t)cur.tv_sec)) * 1000000000L;
+    nsec_diff += ((int64_t)ts->tv_nsec) - ((int64_t)cur.tv_nsec);
+
+    return nsec_diff / 1000000L;
 }
 
 const char *
@@ -231,8 +263,7 @@
     }
 
     if (timeout > 0) {
-        nc_gettimespec_real(&ts_timeout);
-        nc_addtimespec(&ts_timeout, timeout);
+        nc_gettimespec_real_add(&ts_timeout, timeout);
 
         /* LOCK */
         ret = pthread_mutex_timedlock(&session->opts.server.rpc_lock, &ts_timeout);
@@ -308,8 +339,7 @@
     assert(session->opts.server.rpc_inuse);
 
     if (timeout > 0) {
-        nc_gettimespec_real(&ts_timeout);
-        nc_addtimespec(&ts_timeout, timeout);
+        nc_gettimespec_real_add(&ts_timeout, timeout);
 
         /* LOCK */
         ret = pthread_mutex_timedlock(&session->opts.server.rpc_lock, &ts_timeout);
@@ -352,8 +382,7 @@
     struct timespec ts_timeout;
 
     if (timeout > 0) {
-        nc_gettimespec_real(&ts_timeout);
-        nc_addtimespec(&ts_timeout, timeout);
+        nc_gettimespec_real_add(&ts_timeout, timeout);
 
         ret = pthread_mutex_timedlock(session->io_lock, &ts_timeout);
     } else if (!timeout) {
@@ -396,22 +425,20 @@
 {
     int ret;
     int32_t diff_msec;
-    struct timespec ts_timeout, ts_start, ts_end;
+    struct timespec ts_timeout, ts_start;
 
     assert(session->side == NC_CLIENT);
 
     if (*timeout > 0) {
         /* get current time */
-        nc_gettimespec_real(&ts_start);
+        nc_gettimespec_real_add(&ts_start, 0);
 
-        nc_gettimespec_real(&ts_timeout);
-        nc_addtimespec(&ts_timeout, *timeout);
+        nc_gettimespec_real_add(&ts_timeout, *timeout);
 
         ret = pthread_mutex_timedlock(&session->opts.client.msgs_lock, &ts_timeout);
         if (!ret) {
             /* update timeout based on what was elapsed */
-            nc_gettimespec_real(&ts_end);
-            diff_msec = nc_difftimespec(&ts_start, &ts_end);
+            diff_msec = nc_difftimespec_cur(&ts_start);
             *timeout -= diff_msec;
         }
     } else if (!*timeout) {
@@ -671,7 +698,7 @@
     struct nc_session *siter;
     struct nc_msg_cont *contiter;
     struct ly_in *msg;
-    struct timespec ts, ts_cur;
+    struct timespec ts;
     void *p;
 
     if (!session || (session->status == NC_STATUS_CLOSING)) {
@@ -684,12 +711,10 @@
         ATOMIC_STORE_RELAXED(session->opts.client.ntf_thread, 2);
 
         /* wait for it */
-        nc_gettimespec_mono(&ts);
-        nc_addtimespec(&ts, NC_SESSION_FREE_LOCK_TIMEOUT);
+        nc_gettimespec_mono_add(&ts, NC_SESSION_FREE_LOCK_TIMEOUT);
         while (ATOMIC_LOAD_RELAXED(session->opts.client.ntf_thread)) {
             usleep(NC_TIMEOUT_STEP);
-            nc_gettimespec_mono(&ts_cur);
-            if (nc_difftimespec(&ts_cur, &ts) < 1) {
+            if (nc_difftimespec_cur(&ts) < 1) {
                 ERR(session, "Waiting for notification thread exit failed (timed out).");
                 break;
             }
@@ -770,8 +795,7 @@
     if ((session->side == NC_SERVER) && (session->flags & NC_SESSION_CH_THREAD)) {
         pthread_cond_signal(&session->opts.server.ch_cond);
 
-        nc_gettimespec_real(&ts);
-        nc_addtimespec(&ts, NC_SESSION_FREE_LOCK_TIMEOUT);
+        nc_gettimespec_real_add(&ts, NC_SESSION_FREE_LOCK_TIMEOUT);
 
         /* wait for CH thread to actually wake up and terminate */
         r = 0;