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leapsecs.3
leapsecs - handle UTC leap seconds
#include <leapsecs.h>
int leapsecs_sub(&t);
void leapsecs_add(&t,hit);
int leapsecs_read();
int leapsecs_init();
struct tai t;
int hit;
leapsecs_sub changes a seconds-since-epoch count into a non-leap-seconds-since-epoch count. It interprets t as a TAI64 label, subtracts from t the number of leap seconds that have occurred before or at t, and places the result back into t.
leapsecs_sub returns 1 if t was a leap second, 0 otherwise.
leapsecs_add reverses the effect of leapsecs_sub. hit must be 1 for a leap second, 0 otherwise.
The current implementation of leapsecs_sub and leapsecs_add uses a leap-second table read from disk.
leapsecs_read reads the leap-second table from /etc/leapsecs.dat. It returns 0 on success, -1 on error. If /etc/leapsecs.dat does not exist, leapsecs_read treats it as an empty file.
leapsecs_init is a one-time version of leapsecs_read. Initially it is the same as leapsecs_read; however, once leapsecs_read returns 0, leapsecs_init will always return 0 without calling leapsecs_read again.
leapsecs_add and leapsecs_sub call leapsecs_init. WARNING: If leapsecs_init returns failure, leapsecs_add and leapsecs_sub will proceed without a leap-second table. For reliability, all programs should call leapsecs_init at startup and check for errors.
WARNING: New entries are added to the leap-second table on disk every 12 to 18 months. leapsecs_read may be called repeatedly. It leaves the old table alone on error. For reliability, all long-running programs should call leapsecs_read at least once every month.