inverted gmtime?

[mrose%udel-eecis2.delaware at UDEL-RELAY.ARPA]

    I'm looking for a routine that will take a (struct tm *) and return
    a long.  That is, I want the inverse of localtime() or gmtime().

    Does anyone have such a routine?  

    Thanks in advance,

/mtr

    ps: please reply to me only, I don't think this interests the
    general readership of the list.