private bool IsValidLength(long len)
{
if (len == 0x8000) return true;
else if (len == 0x10000) return true;
else if (len == 0x20000) return true;
else if (len == 0x40000) return true;
else if (len == 0x80000) return true;
else if (len == 0x100000) return true;
else if (len == 0x200000) return true;
return false;
}