How to generate Unix time from dates?

[Ray Shwake]

cpcahil at virtech.uucp (Conor P. Cahill) writes:

>The value returned by time(2) is the number of seconds (not microsecs) that
>have past since 12 Midnight December 31, 1969 GMT.  There is no way to use
>this value to represent date/times prior to that date.

	Some time back I wrote a 'unixtime' utility which generated both
ASCII and long integer UNIX times, plus supported "time shifts" in hours,
minutes and seconds. Source and manual page available to those interested.
Doesn't, however, support time before UNIX time 0L noted above.