diff --git a/moo/lib/moo-cmn.h b/moo/lib/moo-cmn.h
index dda7a4a..fd7c905 100644
--- a/moo/lib/moo-cmn.h
+++ b/moo/lib/moo-cmn.h
@@ -614,11 +614,18 @@ typedef struct moo_obj_t*          moo_oop_t;
 #define MOO_SEC_TO_USEC(sec) ((sec) * MOO_USECS_PER_SEC)
 #define MOO_USEC_TO_SEC(usec) ((usec) / MOO_USECS_PER_SEC)
 
+#if defined(MOO_SIZEOF_INT64_T) && (MOO_SIZEOF_INT64_T > 0)
+typedef moo_int64_t moo_ntime_sec_t;
+#else
+typedef moo_int32_t moo_ntime_sec_t;
+#endif
+typedef moo_int32_t moo_ntime_nsec_t;
+
 typedef struct moo_ntime_t moo_ntime_t;
 struct moo_ntime_t
 {
-	moo_intptr_t  sec;
-	moo_int32_t   nsec; /* nanoseconds */
+	moo_ntime_sec_t  sec;
+	moo_ntime_nsec_t   nsec; /* nanoseconds */
 };
 
 #define MOO_INIT_NTIME(c,s,ns) (((c)->sec = (s)), ((c)->nsec = (ns)))
diff --git a/moo/lib/moo-utl.h b/moo/lib/moo-utl.h
index 4297cca..92ecf71 100644
--- a/moo/lib/moo-utl.h
+++ b/moo/lib/moo-utl.h
@@ -875,6 +875,34 @@ MOO_EXPORT int moo_conv_mb8_to_ucstr (
 	moo_oow_t*         ucslen
 );
 
+/* =========================================================================
+ * TIME CALCULATION WITH OVERFLOW/UNDERFLOW DETECTION
+ * ========================================================================= */
+
+/** 
+ * The moo_add_ntime() function adds two time structures pointed to by \a x and \a y
+ * and stores the result in the structure pointed to by \a z. If it detects overflow/
+ * underflow, it stores the largest/least possible value respectively.
+ * You may use the MOO_ADD_NTIME() macro if overflow/underflow check isn't needed.
+ */
+MOO_EXPORT void moo_add_ntime (
+	moo_ntime_t*       z, 
+	const moo_ntime_t* x,
+	const moo_ntime_t* y
+);
+
+/** 
+ * The moo_sub_ntime() function subtracts the time value \a y from the time value \a x
+ * and stores the result in the structure pointed to by \a z. If it detects overflow/
+ * underflow, it stores the largest/least possible value respectively.
+ * You may use the MOO_SUB_NTIME() macro if overflow/underflow check isn't needed.
+ */
+MOO_EXPORT void moo_sub_ntime (
+	moo_ntime_t*       z,
+	const moo_ntime_t* x,
+	const moo_ntime_t* y
+);
+
 /* =========================================================================
  * BIT SWAP
  * ========================================================================= */
diff --git a/moo/lib/utl.c b/moo/lib/utl.c
index ddcfacd..1ab6619 100644
--- a/moo/lib/utl.c
+++ b/moo/lib/utl.c
@@ -1314,3 +1314,115 @@ int moo_copyoocharstosbuf (moo_t* moo, const moo_ooch_t* ptr, moo_oow_t len, moo
 	moo->sbuf[id].len = 0;
 	return moo_concatoocharstosbuf(moo, ptr, len, id);
 }
+
+
+/* ----------------------------------------------------------------------- */
+
+void moo_add_ntime (moo_ntime_t* z, const moo_ntime_t* x, const moo_ntime_t* y)
+{
+	moo_ntime_sec_t xs, ys;
+	moo_ntime_nsec_t ns;
+
+	/*MOO_ASSERT (x->nsec >= 0 && x->nsec < MOO_NSECS_PER_SEC);
+	MOO_ASSERT (y->nsec >= 0 && y->nsec < MOO_NSECS_PER_SEC);*/
+
+	ns = x->nsec + y->nsec;
+	if (ns >= MOO_NSECS_PER_SEC)
+	{
+		ns = ns - MOO_NSECS_PER_SEC;
+		if (x->sec == MOO_TYPE_MAX(moo_ntime_sec_t))
+		{
+			if (y->sec >= 0) goto overflow;
+			xs = x->sec;
+			ys = y->sec + 1; /* this won't overflow */
+		}
+		else
+		{
+			xs = x->sec + 1; /* this won't overflow */
+			ys = y->sec;
+		}
+	}
+	else
+	{
+		xs = x->sec;
+		ys = y->sec;
+	}
+
+	if ((ys >= 1 && xs > MOO_TYPE_MAX(moo_ntime_sec_t) - ys) ||
+	    (ys <= -1 && xs < MOO_TYPE_MIN(moo_ntime_sec_t) - ys))
+	{
+		if (xs >= 0)
+		{
+		overflow:
+			xs = MOO_TYPE_MAX(moo_ntime_sec_t);
+			ns = MOO_NSECS_PER_SEC - 1;
+		}
+		else
+		{
+			xs = MOO_TYPE_MIN(moo_ntime_sec_t);
+			ns = 0;
+		}
+	}
+	else
+	{
+		xs = xs + ys;
+	}
+
+	z->sec = xs;
+	z->nsec = ns;
+}
+
+void moo_sub_ntime (moo_ntime_t* z, const moo_ntime_t* x, const moo_ntime_t* y)
+{
+	moo_ntime_sec_t xs, ys;
+	moo_ntime_nsec_t ns;
+
+	/*MOO_ASSERT (x->nsec >= 0 && x->nsec < MOO_NSECS_PER_SEC);
+	MOO_ASSERT (y->nsec >= 0 && y->nsec < MOO_NSECS_PER_SEC);*/
+
+	ns = x->nsec - y->nsec;
+	if (ns < 0)
+	{
+		ns = ns + MOO_NSECS_PER_SEC;
+		if (x->sec == MOO_TYPE_MIN(moo_ntime_sec_t))
+		{
+			if (y->sec <= 0) goto underflow;
+			xs = x->sec;
+			ys = y->sec - 1; /* this won't underflow */
+		}
+		else
+		{
+			xs = x->sec - 1; /* this won't underflow */
+			ys = y->sec;
+		}
+	}
+	else
+	{
+		xs = x->sec;
+		ys = y->sec;
+	}
+
+	if ((ys >= 1 && xs < MOO_TYPE_MIN(moo_ntime_sec_t) + ys) ||
+	    (ys <= -1 && xs > MOO_TYPE_MAX(moo_ntime_sec_t) + ys))
+	{
+		if (xs >= 0)
+		{
+			xs = MOO_TYPE_MAX(moo_ntime_sec_t);
+			ns = MOO_NSECS_PER_SEC - 1;
+		}
+		else
+		{
+		underflow:
+			xs = MOO_TYPE_MIN(moo_ntime_sec_t);
+			ns = 0;
+		}
+	} 
+	else
+	{
+		xs = xs - ys;
+	}
+
+	z->sec = xs;
+	z->nsec = ns;
+}
+