These functions are inspired by C standard interfaces named similarly.
offtime() converts the calendar time
clock, offset by
offset seconds, into broken-down time, expressed as Coordinated Universal Time (UTC).
timeoff() converts the broken-down time
tm, expressed as UTC, offset by
offset seconds, into a calendar time value.
timegm() converts the broken-down time
tm into a calendar time value, effectively being the inverse of
gmtime(3). It is equivalent to the C standard function
mktime(3) operating in UTC.
timelocal() converts the broken down time
tm, expressed as local time, into a calendar time value. It is equivalent to the C standard function
mktime(3), and is provided for symmetry only.