lib/timeutils: Add helper functions to deal with nanosecs since 1970.

Signed-off-by: Damien George <damien@micropython.org>

lib/timeutils/timeutils.h

@@ -27,6 +27,10 @@
 #ifndef MICROPY_INCLUDED_LIB_TIMEUTILS_TIMEUTILS_H
 #define MICROPY_INCLUDED_LIB_TIMEUTILS_TIMEUTILS_H
 
+// The number of seconds between 1970/1/1 and 2000/1/1 is calculated using:
+// time.mktime((2000,1,1,0,0,0,0,0,0)) - time.mktime((1970,1,1,0,0,0,0,0,0))
+#define TIMEUTILS_SECONDS_1970_TO_2000 (946684800ULL)
+
 typedef struct _timeutils_struct_time_t {
     uint16_t tm_year;       // i.e. 2014
     uint8_t tm_mon;         // 1..12
@@ -38,6 +42,14 @@ typedef struct _timeutils_struct_time_t {
     uint16_t tm_yday;       // 1..366
 } timeutils_struct_time_t;
 
+static inline uint64_t timeutils_seconds_since_2000_to_nanoseconds_since_1970(mp_uint_t s) {
+    return ((uint64_t)s + TIMEUTILS_SECONDS_1970_TO_2000) * 1000000000ULL;
+}
+
+static inline mp_uint_t timeutils_seconds_since_2000_from_nanoseconds_since_1970(uint64_t ns) {
+    return ns / 1000000000ULL - TIMEUTILS_SECONDS_1970_TO_2000;
+}
+
 bool timeutils_is_leap_year(mp_uint_t year);
 mp_uint_t timeutils_days_in_month(mp_uint_t year, mp_uint_t month);
 mp_uint_t timeutils_year_day(mp_uint_t year, mp_uint_t month, mp_uint_t date);
@@ -51,4 +63,10 @@ mp_uint_t timeutils_seconds_since_2000(mp_uint_t year, mp_uint_t month,
 mp_uint_t timeutils_mktime(mp_uint_t year, mp_int_t month, mp_int_t mday,
     mp_int_t hours, mp_int_t minutes, mp_int_t seconds);
 
+static inline uint64_t timeutils_nanoseconds_since_1970(mp_uint_t year, mp_uint_t month,
+    mp_uint_t date, mp_uint_t hour, mp_uint_t minute, mp_uint_t second) {
+    return timeutils_seconds_since_2000_to_nanoseconds_since_1970(
+        timeutils_seconds_since_2000(year, month, date, hour, minute, second));
+}
+
 #endif // MICROPY_INCLUDED_LIB_TIMEUTILS_TIMEUTILS_H