New data_type coap_time_diff_t and functions coap_time_lt(), coap_time_le()

for time stamps with wrapping

coap_time.h

@@ -28,6 +28,13 @@
 
 typedef clock_time_t coap_tick_t;
 
+/**
+ * This data type is used to represent the difference between two
+ * clock_tick_t values. This data type must have the same size in
+ * memory as coap_tick_t to allow wrapping.
+ */
+typedef int coap_tick_diff_t;
+
 #define COAP_TICKS_PER_SECOND CLOCK_SECOND
 
 /** Set at startup to initialize the internal clock (time in seconds). */
@@ -51,6 +58,13 @@ contiki_ticks_impl(coap_tick_t *t) {
 #else /* WITH_CONTIKI */
 typedef unsigned int coap_tick_t; 
 
+/**
+ * This data type is used to represent the difference between two
+ * clock_tick_t values. This data type must have the same size in
+ * memory as coap_tick_t to allow wrapping.
+ */
+typedef int coap_tick_diff_t;
+
 #define COAP_TICKS_PER_SECOND 1024
 
 /** Set at startup to initialize the internal clock (time in seconds). */
@@ -89,6 +103,16 @@ coap_ticks_impl(coap_tick_t *t) {
 #define coap_ticks coap_ticks_impl
 #endif /* coap_ticks */
 
+static inline
+int coap_time_lt(coap_tick_t a, coap_tick_t b) {
+  return ((coap_tick_diff_t)(a - b)) < 0;
+}
+
+static inline
+int coap_time_le(coap_tick_t a, coap_tick_t b) {
+  return a == b || coap_time_lt(a,b);
+}
+
 /** @} */
 
 #endif /* _COAP_TIME_H_ */