first talk your new company's boss your situation he will surely agreed with you. if they want some proof of your working then you may present them your appointment letter or salary slip as a evidance. If they aggreed then do one thing first give resignation from your present company and take its aknolwledgement. If your current boss refuse to give aknolwedgement then one copy of resignation send by regd post or by email, means you have retain some proof that you have submited resign. Put your last working day in that and metioned that company can adjust shortfall period whatever it may be in your full and final settlement.
pankaj
pankaj