Unix time question

[Jeffrey W Percival]

I have a date string, of the form yymmddhhmmss.ss

How do I convert this into the number of seconds since the Unix epoch?

In other words, gettimeofday(2) gives me the *current* time in elapsed
seconds...  I want the number of elapsed seconds represented by my
date string.

date(1) does this, but I don't have source.  TFM doesn't seem to cover this.
-- 
Jeff Percival (jwp at larry.sal.wisc.edu)