sql query to convert between tz

Hi ,

I need to write an function which will convert a given date from gmt to est and est to gmt timezone. I have to take care of daylight savings also.

Iam using new_time as below

v_est:= new_time(sysdate,'gmt','est')
v_gmt:= new_time(sysdate,'est'.'gmt'). But this function does not handle day light saving.

My function needs to handle the below condition,

I have to check whether daylight saving needs to be applied based on the diff between dates in various timezone and then apply it while converting it from gmt to est and est to gmt.
else
do not apply daylight saving, directly converting between gmt and est and est and gmt.
end if;

any help is really appraciated.