C++: Check a valid date

C++ has no checkdate, like php does. so i wrote this to filter out bad dates and feb29ths.

bool isValidDate(int m, int d, int y)
{
  //checks Gregorian date
  if (! (1582<= y )  )
     return false;
  if (! (1<= m && m<=12) )
     return false;
  if (! (1<= d && d<=31) )
     return false;
  if ( (d==31) && (m==2 || m==4 || m==6 || m==9 || m==11) )
     return false;
  if ( (d==30) && (m==2) )
     return false;
  if ( (m==2) && (d==29) && (y%4!=0) )
     return false;
  if ( (m==2) && (d==29) && (y%400==0) )
     return true;
  if ( (m==2) && (d==29) && (y%100==0) )
     return false;
  if ( (m==2) && (d==29) && (y%4==0)  )
     return true;

  return true;
}

source(s): http://en.wikipedia.org/wiki/Leap_year