Make TIMESTAMP + TIME in the source code

Hello, I'm writinng again because I need to make some validation for
the incoming data (VALUES... on the INSERT-Stmt). This validation
is based on adding a TIMESTAMP and a TIME kind of data.

From the Shell I can make:

template1=# select timestamp '02/03/85 7:00pm'+'00:00:02.3450' as
"TIMESTAMP+TIME";

And that would give me the next result:

TIMESTAMP+TIME
-------------------------
1985-02-03 19:00:02.345

That's exactly wath I need to do, obtain the result from adding a TIMESTAMP
and a TIME, but I must do it from the Postgre's source code, since I'm
working
on modifying Postgres for a University Project (here in Venezuela we call it
"Tesis" or "Graduation Special Work".

Due to this, I need to know if there's a special function on Postgre's
backend
code that can do this.

Greetings, I hope you could help me on this.

PD: in adition, both data (TIMESTAMP and TIME) are stored in strings (char
*).
The TIME is stored on the pg_class structure (thanks to a modification I
made),
and the TIMESTAMP is given on the INSERT values.
--
Luis D. García M.

Telf: (+58) 2418662663
Cel.: (+58) 4143482018

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