SQL & PL/SQL

Hello,

Is there a SQL or PL/SQL function to convert an Oracle DATE time representing local time to a number representing elapsed seconds since the Epoch (defined 1st Jan 1970 00:00 GMT) and vice-versa? I 've got some files with date (local times) stored in traditional formats and the database uniformly handles all date fields as NUMBER representing elapsed seconds since the Epoch. Note that 0 seconds since the epoch is 1st Jan 1970 00:00 in GMT time but should be, say 1st Jan 1970 03:00 for Eastern European Time zone (which is GMT+3 half of the calendar year and GMT+2 the other half according to daylight saving)

Thanks.