DST settings for php(Codeigniter)

I am working on a world clock module in php(codeigniter). I need to display times according to timezone which people select in a drop box. I have completed that, but facing a problem with DST(day light saving) settings. How do i get to know weather that particular timezone has DST for it or not. Kindly help me with this point as I am from India and not familiar with day light savings. Infact go开发者_JS百科t to know about day light saving after working on this project. LOL.. Kindly help.

I (capital i) - Whether or not the date is in daylight saving time - 1 if Daylight Saving Time, 0 otherwise.