Compute Leap Seconds

I use PostgreSQL 11 and have two columns. One is unix timestamp which is not aware of leap seconds and an utc timestamp which is aware of leap seconds. Is there a way either to find the number of leap seconds between an unix timestamp (without leap Seconds) and an utc timestamp (with leap seconds)? Alternatively is there a way to convert an utc timestamp (with leap seconds) into an unix timestamp (without leap seconds)?