/* For a given year after 2038, pick the latest possible matching
year in the 28 year calendar cycle.
A matching year...
1) Starts on the same day of the week.
2) Has the same leap year status.
This is so the calendars match up.
Also the previous year must match. When doing Jan 1st you might
wind up on Dec 31st the previous year when doing a -UTC time zone.
Finally, the next year must have the same start day of week. This
is for Dec 31st with a +UTC time zone.
It doesn't need the same leap year status since we only care about
January 1st.
*/
static int S_safe_year(Year year)
{
int safe_year;
Year year_cycle = year + S_cycle_offset(year);
/* Change non-leap xx00 years to an equivalent */
if( S_is_exception_century(year) )
year_cycle += 11;
/* Also xx01 years, since the previous year will be wrong */
if( S_is_exception_century(year - 1) )
year_cycle += 17;
year_cycle %= SOLAR_CYCLE_LENGTH;
if( year_cycle < 0 )
year_cycle = SOLAR_CYCLE_LENGTH + year_cycle;
assert( year_cycle >= 0 );
assert( year_cycle < SOLAR_CYCLE_LENGTH );
safe_year = safe_years[year_cycle];
assert(safe_year <= 2037 && safe_year >= 2010);
TIME64_TRACE3("# year: %lld, year_cycle: %lld, safe_year: %d\n",
year, year_cycle, safe_year);
return safe_year;
}
/* The exceptional centuries without leap years cause the cycle to
shift by 16
*/
static Year cycle_offset(Year year)
{
const Year start_year = 2000;
Year year_diff = year - start_year;
Year exceptions;
if( year > start_year )
year_diff--;
exceptions = year_diff / 100;
exceptions -= year_diff / 400;
TIME64_TRACE3("# year: %lld, exceptions: %lld, year_diff: %lld\n",
year, exceptions, year_diff);
return exceptions * 16;
}
/* timegm() is not in the C or POSIX spec, but it is such a useful
extension I would be remiss in leaving it out. Also I need it
for localtime64()
*/
Time64_T timegm64(const struct TM *date) {
Time64_T days = 0;
Time64_T seconds = 0;
Year year;
Year orig_year = (Year)date->tm_year;
int cycles = 0;
if( orig_year > 100 ) {
cycles = (orig_year - 100) / 400;
orig_year -= cycles * 400;
days += (Time64_T)cycles * days_in_gregorian_cycle;
}
else if( orig_year < -300 ) {
cycles = (orig_year - 100) / 400;
orig_year -= cycles * 400;
days += (Time64_T)cycles * days_in_gregorian_cycle;
}
TIME64_TRACE3("# timegm/ cycles: %d, days: %lld, orig_year: %lld\n", cycles, days, orig_year);
if( orig_year > 70 ) {
year = 70;
while( year < orig_year ) {
days += length_of_year[IS_LEAP(year)];
year++;
}
}
else if ( orig_year < 70 ) {
year = 69;
do {
days -= length_of_year[IS_LEAP(year)];
year--;
} while( year >= orig_year );
}
days += julian_days_by_month[IS_LEAP(orig_year)][date->tm_mon];
days += date->tm_mday - 1;
seconds = days * 60 * 60 * 24;
seconds += date->tm_hour * 60 * 60;
seconds += date->tm_min * 60;
seconds += date->tm_sec;
return(seconds);
}
/* For a given year after 2038, pick the latest possible matching
year in the 28 year calendar cycle.
A matching year...
1) Starts on the same day of the week.
2) Has the same leap year status.
This is so the calendars match up.
Also the previous year must match. When doing Jan 1st you might
wind up on Dec 31st the previous year when doing a -UTC time zone.
Finally, the next year must have the same start day of week. This
is for Dec 31st with a +UTC time zone.
It doesn't need the same leap year status since we only care about
January 1st.
*/
static int safe_year(const Year year)
{
int safe_year= (int)year;
Year year_cycle;
if( year >= MIN_SAFE_YEAR && year <= MAX_SAFE_YEAR ) {
return safe_year;
}
year_cycle = year + cycle_offset(year);
/* safe_years_low is off from safe_years_high by 8 years */
if( year < MIN_SAFE_YEAR )
year_cycle -= 8;
/* Change non-leap xx00 years to an equivalent */
if( is_exception_century(year) )
year_cycle += 11;
/* Also xx01 years, since the previous year will be wrong */
if( is_exception_century(year - 1) )
year_cycle += 17;
year_cycle %= SOLAR_CYCLE_LENGTH;
if( year_cycle < 0 )
year_cycle = SOLAR_CYCLE_LENGTH + year_cycle;
assert( year_cycle >= 0 );
assert( year_cycle < SOLAR_CYCLE_LENGTH );
if( year < MIN_SAFE_YEAR )
safe_year = safe_years_low[year_cycle];
else if( year > MAX_SAFE_YEAR )
safe_year = safe_years_high[year_cycle];
else
assert(0);
TIME64_TRACE3("# year: %lld, year_cycle: %lld, safe_year: %d\n",
year, year_cycle, safe_year);
assert(safe_year <= MAX_SAFE_YEAR && safe_year >= MIN_SAFE_YEAR);
return safe_year;
}