The clock gps_clock
seconds since the first Sunday of January, 1980 00:00:00 UTC.
Leap seconds are not inserted into GPS.
Therefore every time a leap second is inserted into UTC,
UTC shifts another second with respect to GPS.
Aside from the offset from 1958y/January/1
GPS is behind TAI by 19s due to the 10s offset between 1958 and 1970
and the additional 9 leap seconds inserted between 1970 and 1980.