TAI, or Temps Atomique International, measures real time with a constant duration defined by cesium radiation since 1955. UTC, Coordinated Universal Time, based on TAI, has leap seconds every year or two to match Earth’s rotation. UNIX time counts seconds since 1970 GMT, making it convenient for time intervals. The UNIX localtime() routine had issues with leap seconds, affecting the xntpd program’s reliability. Fixing the problem is straightforward but hindered by the outdated POSIX standard. The author provides 64-bit time manipulation code to address future disasters and a Network Time Protocol client that handles leap seconds correctly. This content emphasizes precision in time measurement and programming challenges.
https://cr.yp.to/proto/utctai.html