def interpret(self, startpos, args, addr=None, simfd=None):
        """
        implement scanf - extract formatted data from memory or a file according to the stored format
        specifiers and store them into the pointers extracted from `args`.

        :param startpos:    The index of the first argument corresponding to the first format element
        :param args:        A function which, given the index of an argument to the function, returns that argument
        :param addr:        The address in the memory to extract data from, or...
        :param simfd:       A file descriptor to use for reading data from
        :return:            The number of arguments parsed
        """
        if simfd is not None and isinstance(simfd.read_storage, SimPackets):
            argnum = startpos
            for component in self.components:
                if type(component) is bytes:
                    sdata, _ = simfd.read_data(len(component), short_reads=False)
                    self.state.solver.add(sdata == component)
                elif isinstance(component, claripy.Bits):
                    sdata, _ = simfd.read_data(len(component) // 8, short_reads=False)
                    self.state.solver.add(sdata == component)
                elif component.spec_type == b's':
                    if component.length_spec is None:
                        sdata, slen = simfd.read_data(self.state.libc.buf_symbolic_bytes)
                    else:
                        sdata, slen = simfd.read_data(component.length_spec)
                    for byte in sdata.chop(8):
                        self.state.solver.add(claripy.And(*[byte != char for char in self.SCANF_DELIMITERS]))
                    self.state.memory.store(args(argnum), sdata, size=slen)
                    self.state.memory.store(args(argnum) + slen, claripy.BVV(0, 8))
                    argnum += 1
                elif component.spec_type == b'c':
                    sdata, _ = simfd.read_data(1, short_reads=False)
                    self.state.memory.store(args(argnum), sdata)
                    argnum += 1
                else:
                    bits = component.size * 8
                    if component.spec_type == b'x':
                        base = 16
                    elif component.spec_type == b'o':
                        base = 8
                    else:
                        base = 10

                    # here's the variable representing the result of the parsing
                    target_variable = self.state.solver.BVS('scanf_' + component.string.decode(), bits,
                            key=('api', 'scanf', argnum - startpos, component.string))
                    negative = claripy.SLT(target_variable, 0)

                    # how many digits does it take to represent this variable fully?
                    max_digits = int(math.ceil(math.log(2**bits, base)))

                    # how many digits does the format specify?
                    spec_digits = component.length_spec

                    # how many bits can we specify as input?
                    available_bits = float('inf') if spec_digits is None else spec_digits * math.log(base, 2)
                    not_enough_bits = available_bits < bits

                    # how many digits will we model this input as?
                    digits = max_digits if spec_digits is None else spec_digits

                    # constrain target variable range explicitly if it can't take on all possible values
                    if not_enough_bits:
                        self.state.solver.add(self.state.solver.And(
                            self.state.solver.SLE(target_variable, (base**digits) - 1),
                            self.state.solver.SGE(target_variable, -(base**(digits - 1) - 1))))

                    # perform the parsing in reverse - constrain the input digits to be the string version of the input
                    # this only works because we're reading from a packet stream and therefore nobody has the ability
                    # to add other constraints to this data!
                    # this makes z3's job EXTREMELY easy
                    sdata, _ = simfd.read_data(digits, short_reads=False)
                    for i, digit in enumerate(reversed(sdata.chop(8))):
                        digit_value = (target_variable // (base**i)) % base
                        digit_ascii = digit_value + ord('0')
                        if base > 10:
                            digit_ascii = claripy.If(digit_value >= 10, digit_value + (-10 + ord('a')), digit_ascii)

                        # if there aren't enough bits, we can increase the range by accounting for the possibility that
                        # the first digit is a minus sign
                        if not_enough_bits:
                            if i == digits - 1:
                                neg_digit_ascii = ord('-')
                            else:
                                neg_digit_value = (-target_variable // (base**i)) % base
                                neg_digit_ascii = neg_digit_value + ord('0')
                                if base > 10:
                                    neg_digit_ascii = claripy.If(neg_digit_value >= 10, neg_digit_value + (-10 + ord('a')), neg_digit_ascii)

                            digit_ascii = claripy.If(negative, neg_digit_ascii, digit_ascii)

                        self.state.solver.add(digit == digit_ascii[7:0])

                    self.state.memory.store(args(argnum), target_variable, endness=self.state.arch.memory_endness)
                    argnum += 1

            return argnum - startpos

        # TODO: we only support one format specifier in interpretation for now

        format_specifier_count = sum(1 for x in self.components if isinstance(x, FormatSpecifier))
        if format_specifier_count > 1:
            l.warning("We don't support more than one format specifiers in format strings.")

        if simfd is not None:
            region = simfd.read_storage
            addr = simfd._pos if hasattr(simfd, '_pos') else simfd._read_pos # XXX THIS IS BAD
        else:
            region = self.parser.state.memory

        bits = self.parser.state.arch.bits
        failed = self.parser.state.solver.BVV(0, bits)
        argpos = startpos
        position = addr
        for component in self.components:
            if isinstance(component, bytes):
                # TODO we skip non-format-specifiers in format string interpretation for now
                # if the region doesn't match the concrete component, we need to return immediately
                pass
            else:
                fmt_spec = component
                try:
                    dest = args(argpos)
                except SimProcedureArgumentError:
                    dest = None
                if fmt_spec.spec_type == b's':
                    # set some limits for the find
                    max_str_len = self.parser.state.libc.max_str_len
                    max_sym_bytes = self.parser.state.libc.buf_symbolic_bytes

                    # has the length of the format been limited by the string itself?
                    if fmt_spec.length_spec is not None:
                        max_str_len = fmt_spec.length_spec
                        max_sym_bytes = fmt_spec.length_spec

                    # TODO: look for limits on other characters which scanf is sensitive to, '\x00', '\x20'
                    ohr, ohc, ohi = region.find(position, self.parser.state.solver.BVV(b'\n'), max_str_len, max_symbolic_bytes=max_sym_bytes)

                    # if no newline is found, mm is position + max_strlen
                    # If-branch will really only happen for format specifiers with a length
                    mm = self.parser.state.solver.If(ohr == 0, position + max_str_len, ohr)
                    # we're just going to concretize the length, load will do this anyways
                    length = self.parser.state.solver.max_int(mm - position)
                    src_str = region.load(position, length)

                    # TODO all of these should be delimiters we search for above
                    # add that the contents of the string cannot be any scanf %s string delimiters
                    for delimiter in set(FormatString.SCANF_DELIMITERS):
                        delim_bvv = self.parser.state.solver.BVV(delimiter)
                        for i in range(length):
                            self.parser.state.add_constraints(region.load(position + i, 1) != delim_bvv)

                    # write it out to the pointer
                    self.parser.state.memory.store(dest, src_str)
                    # store the terminating null byte
                    self.parser.state.memory.store(dest + length, self.parser.state.solver.BVV(0, 8))

                    position += length

                else:

                    # XXX: atoi only supports strings of one byte
                    if fmt_spec.spec_type in [b'd', b'i', b'u', b'x']:
                        base = 16 if fmt_spec.spec_type == b'x' else 10
                        status, i, num_bytes = self.parser._sim_atoi_inner(position, region, base=base, read_length=fmt_spec.length_spec)
                        # increase failed count if we were unable to parse it
                        failed = self.parser.state.solver.If(status, failed, failed + 1)
                        position += num_bytes
                    elif fmt_spec.spec_type == b'c':
                        i = region.load(position, 1)
                        i = i.zero_extend(bits - 8)
                        position += 1
                    else:
                        raise SimProcedureError("unsupported format spec '%s' in interpret" % fmt_spec.spec_type)

                    i = self.parser.state.solver.Extract(fmt_spec.size*8-1, 0, i)
                    self.parser.state.memory.store(dest, i, size=fmt_spec.size, endness=self.parser.state.arch.memory_endness)

                argpos += 1

        if simfd is not None:
            simfd.read_data(position - addr)

        return (argpos - startpos) - failed
implement scanf - extract formatted data from memory or a file according to the stored format
        specifiers and store them into the pointers extracted from `args`.

        :param startpos:    The index of the first argument corresponding to the first format element
        :param args:        A function which, given the index of an argument to the function, returns that argument
        :param addr:        The address in the memory to extract data from, or...
        :param simfd:       A file descriptor to use for reading data from
        :return:            The number of arguments parsed