+
+static inline usec_t usec_add(usec_t a, usec_t b) {
+ usec_t c;
+
+ /* Adds two time values, and makes sure USEC_INFINITY as input results as USEC_INFINITY in output, and doesn't
+ * overflow. */
+
+ c = a + b;
+ if (c < a || c < b) /* overflow check */
+ return USEC_INFINITY;
+
+ return c;
+}
+
+static inline usec_t usec_sub_unsigned(usec_t timestamp, usec_t delta) {
+
+ if (timestamp == USEC_INFINITY) /* Make sure infinity doesn't degrade */
+ return USEC_INFINITY;
+ if (timestamp < delta)
+ return 0;
+
+ return timestamp - delta;
+}
+
+static inline usec_t usec_sub_signed(usec_t timestamp, int64_t delta) {
+ if (delta < 0)
+ return usec_add(timestamp, (usec_t) (-delta));
+ else
+ return usec_sub_unsigned(timestamp, (usec_t) delta);
+}
+
+#if SIZEOF_TIME_T == 8
+/* The last second we can format is 31. Dec 9999, 1s before midnight, because otherwise we'd enter 5 digit year
+ * territory. However, since we want to stay away from this in all timezones we take one day off. */
+#define USEC_TIMESTAMP_FORMATTABLE_MAX ((usec_t) 253402214399000000)
+#elif SIZEOF_TIME_T == 4
+/* With a 32bit time_t we can't go beyond 2038... */
+#define USEC_TIMESTAMP_FORMATTABLE_MAX ((usec_t) 2147483647000000)
+#else
+#error "Yuck, time_t is neither 4 not 8 bytes wide?"
+#endif