diff options
Diffstat (limited to 'include/ntp_calendar.h')
| -rw-r--r-- | include/ntp_calendar.h | 73 |
1 files changed, 71 insertions, 2 deletions
diff --git a/include/ntp_calendar.h b/include/ntp_calendar.h index 0b1f20d6bd7b7..cc7977aff4818 100644 --- a/include/ntp_calendar.h +++ b/include/ntp_calendar.h @@ -19,6 +19,8 @@ struct calendar { uint8_t second; /* second of minute */ uint8_t weekday; /* 0..7, 0=Sunday */ }; +typedef struct calendar TCivilDate; +typedef struct calendar const TcCivilDate; /* ISO week calendar date */ struct isodate { @@ -29,6 +31,8 @@ struct isodate { uint8_t minute; /* minute of hour */ uint8_t second; /* second of minute */ }; +typedef struct isodate TIsoDate; +typedef struct isodate const TcIsoDate; /* general split representation */ typedef struct { @@ -109,6 +113,7 @@ extern systime_func_ptr ntpcal_set_timefunc(systime_func_ptr); extern const char * const months[12]; extern const char * const daynames[7]; +extern char * ntpcal_iso8601std(char*, size_t, struct calendar const*); extern void caljulian (uint32_t, struct calendar *); extern uint32_t caltontp (const struct calendar *); @@ -152,12 +157,26 @@ extern ntpcal_split ntpcal_daysplit(const vint64 *); /* + * Split a time stamp in seconds into elapsed weeks and elapsed seconds + * since start of week. + */ +extern ntpcal_split +ntpcal_weeksplit(const vint64 *); + +/* * Merge a number of days and a number of seconds into seconds, * expressed in 64 bits to avoid overflow. */ extern vint64 ntpcal_dayjoin(int32_t /* days */, int32_t /* seconds */); +/* + * Merge a number of weeks and a number of seconds into seconds, + * expressed in 64 bits to avoid overflow. + */ +extern vint64 +ntpcal_weekjoin(int32_t /* weeks */, int32_t /* seconds */); + /* Get the number of leap years since epoch for the number of elapsed * full years */ @@ -431,7 +450,7 @@ basedate_expand_gpsweek(unsigned short weekno); /* * Start day of the GPS epoch. This is the Rata Die of 1980-01-06 */ -#define DAY_GPS_STARTS 722819 +#define DAY_GPS_STARTS 722820 /* * Difference between UN*X and NTP epoch (25567). @@ -467,6 +486,56 @@ basedate_expand_gpsweek(unsigned short weekno); */ #define GREGORIAN_CYCLE_WEEKS (GREGORIAN_CYCLE_DAYS / 7) -#define is_leapyear(y) (!((y) % 4) && !(!((y) % 100) && (y) % 400)) +/* + * Is a Greogorian calendar year a leap year? The obvious solution is to + * test the expression + * + * (y % 4 == 0) && ((y % 100 != 0) || (y % 400 == 0)) + * + * This needs (in theory) 2 true divisions -- most compilers check the + * (mod 4) condition by doing a bit test. Some compilers have been + * even observed to partially fuse the (mod 100) and (mod 400) test, + * but there is an alternative formula that gives the compiler even + * better chances: + * + * (y % 4 == 0) && ((y % 16 == 0) || (y % 25 != 0)) + * + * The order of checks is chosen so that the shorcut evaluation can fix + * the result as soon as possible. And the compiler has to do only one + * true division here -- the (mod 4) and (mod 16) can be done with + * direct bit tests. *If* the compiler chooses to do so. + * + * The deduction is as follows: rewrite the standard formula as + * (y % 4 == 0) && ((y % 4*25 != 0) || (y % 16*25 == 0)) + * + * then split the congruences: + * (y % 4 == 0) && ((y % 4 != 0 || y % 25 != 0) || (y % 16 == 0 && y % 25 == 0)) + * + * eliminate the 1st inner term, as it is provably false: + * (y % 4 == 0) && (y % 25 != 0 || (y % 16 == 0 && y % 25 == 0)) + * + * Use the distributive laws on the second major group: + * (y % 4 == 0) && ((y % 25 != 0 || y % 16 == 0) && (y % 25 != 0 || y % 25 == 0)) + * + * Eliminate the constant term, reorder, and voila: + */ + +static inline int +is_leapyear(int32_t y) { + return !(y % 4) && (!(y % 16) || (y % 25)); +} +/* The (mod 4) test eliminates 3/4 (or 12/16) of all values. + * The (mod 16) test eliminates another 1/16 of all values. + * 3/16 of all values reach the final division. + * Assuming that the true division is the most costly operation, this + * sequence should give most bang for the buck. + */ + +/* misc */ +extern int u32mod7(uint32_t x); +extern int i32mod7(int32_t x); +extern uint32_t i32fmod(int32_t x, uint32_t d); + +extern int32_t ntpcal_expand_century(uint32_t y, uint32_t m, uint32_t d, uint32_t wd); #endif |