def btreeSearch(self, ip):
        """
        " b-tree search method
        " param: ip
        """
        if not ip.isdigit(): ip = self.ip2Long(ip)

        if len(self.__headerSip) < 1:
            #pass the super block
            self.__f.seek(8)
            #read the header block
            b = self.__f.read(8192)
            #parse the header block
            sip = None
            ptr = None
            for i in range(0, len(b)-1, 8):
                sip = self.getLong(b, i)
                ptr = self.getLong(b, i+4)
                if ptr == 0:
                    break
                self.__headerSip.append(sip)
                self.__headerPtr.append(ptr)

        headerLen = len(self.__headerSip) - 1
        l, h, sptr, eptr = (0, headerLen, 0, 0)
        while l <= h:
            m = int((l+h)/2)

            if ip == self.__headerSip[m]:
                if m > 0:
                    sptr = self.__headerPtr[m-1]
                    eptr = self.__headerPtr[m]
                    break;
                else:
                    sptr = self.__headerPtr[m]
                    eptr = self.__headerPtr[m+1]
                    break;

            if ip > self.__headerSip[m]:
                if m == headerLen:
                    sptr = self.__headerPtr[m-1]
                    eptr = self.__headerPtr[m]
                    break;
                elif ip < self.__headerSip[m+1]:
                    sptr = self.__headerPtr[m]
                    eptr = self.__headerPtr[m+1]
                    break;

                l = m + 1
            else:
                if m == 0:
                    sptr = self.__headerPtr[m]
                    eptr = self.__headerPtr[m+1]
                    break;
                elif ip > self.__headerSip[m-1]:
                    sptr = self.__headerPtr[m-1]
                    eptr = self.__headerPtr[m]
                    break;

                h = m - 1

        if sptr == 0: return "N1"

        indexLen = eptr - sptr
        self.__f.seek(sptr)
        b = self.__f.read(indexLen + 12)

        l, h, mixPtr = (0, int(indexLen/12), 0)
        while l <= h:
            m = int((l+h)/2)
            offset = m * 12

            if ip >= self.getLong(b, offset):
                if ip > self.getLong(b, offset+4):
                    l = m + 1
                else:
                    mixPtr = self.getLong(b, offset+8)
                    break;
            else:
                h = m - 1

        if mixPtr == 0: return "N2"

        return self.returnData(mixPtr)
" b-tree search method
        " param: ip