bgneal@0: #ifndef CPP_ENIGMA_ROTOR_H
bgneal@0: #define CPP_ENIGMA_ROTOR_H
bgneal@0: // Copyright (C) 2012 by Brian Neal.
bgneal@0: // This file is part of Cpp-Enigma, the Enigma Machine simulation.
bgneal@0: // Cpp-Enigma is released under the MIT License (see License.txt).
bgneal@0: //
bgneal@0: // rotor.h - This file contains the rotor class.
bgneal@0: 
bgneal@0: #include <string>
bgneal@0: #include "enigma_types.h"
bgneal@0: 
bgneal@0: 
bgneal@0: namespace enigma
bgneal@0: {
bgneal@0:    class rotor_error : public enigma_error
bgneal@0:    {
bgneal@0:    public:
bgneal@0:       explicit rotor_error(const std::string& what_arg)
bgneal@0:        : enigma_error(what_arg)
bgneal@0:       {}
bgneal@0:    };
bgneal@0: 
bgneal@0:    // The rotor class represents the Enigma Machine rotors (Walzen).
bgneal@0:    //
bgneal@0:    // A rotor has 26 circularly arranged pins on the right (entry) side and 26
bgneal@0:    // contacts on the left side. Each pin is connected to a single contact by
bgneal@0:    // internal wiring, thus establishing a substitution cipher. We represent this
bgneal@0:    // wiring by establishing a mapping from a pin to a contact (and vice versa for
bgneal@0:    // the return path). Internally we number the pins and contacts from 0-25 in a
bgneal@0:    // clockwise manner with 0 being the "top".
bgneal@0:    //
bgneal@0:    // An alphabetic or numeric ring is fastened to the rotor by the operator. The
bgneal@0:    // labels of this ring are displayed to the operator through a small window on
bgneal@0:    // the top panel. The ring can be fixed to the rotor in one of 26 different
bgneal@0:    // positions; this is called the ring setting (Ringstellung). We will number
bgneal@0:    // the ring settings from 0-25 where 0 means no offset (e.g. the letter "A" is
bgneal@0:    // mapped to pin 0 on an alphabetic ring). A ring setting of 1 means the letter
bgneal@0:    // "B" is mapped to pin 0.
bgneal@0:    //
bgneal@0:    // Each rotor can be in one of 26 positions on the spindle, with position 0
bgneal@0:    // where pin/contact 0 is being indicated in the operator window. The rotor
bgneal@0:    // rotates towards the operator by mechanical means during normal operation as
bgneal@0:    // keys are being pressed during data entry. Position 1 is thus defined to be
bgneal@0:    // one step from position 0. Likewise, position 25 is the last position before
bgneal@0:    // another step returns it to position 0, completing 1 trip around the spindle.
bgneal@0:    //
bgneal@0:    // Finally, a rotor has a "stepping" or "turnover" parameter. Physically this
bgneal@0:    // is implemented by putting a notch on the alphabet ring and it controls when
bgneal@0:    // the rotor will "kick" the rotor to its left, causing the neighbor rotor to
bgneal@0:    // rotate. Most rotors had one notch, but some Kriegsmarine rotors had 2
bgneal@0:    // notches and thus rotated twice as fast.
bgneal@0:    //
bgneal@0:    // Note that due to the system of ratchets and pawls, the middle rotor (in a 3
bgneal@0:    // rotor Enigma) can "double-step". The middle rotor will advance on the next
bgneal@0:    // step of the first rotor a second time in a row, if the middle rotor is in
bgneal@0:    // its own turnover position.
bgneal@0:    //
bgneal@0:    // Note that we allow the stepping parameter to be None. This indicates the
bgneal@0:    // rotor does not rotate. This allows us to model the entry wheel and
bgneal@0:    // reflectors as stationary rotors.
bgneal@0: 
bgneal@0:    class rotor
bgneal@0:    {
bgneal@0:    public:
bgneal@0:       // rotor constructor:
bgneal@0:       //
bgneal@0:       // model_name - e.g. "I", "II", "III", "Beta", "Gamma"
bgneal@0:       //
bgneal@0:       // wiring - this should be a string of 26 alphabetic characters that
bgneal@0:       // represents the internal wiring transformation of the signal as it enters
bgneal@0:       // from the right side. This is the format used in various online
bgneal@0:       // resources. For example, for the Wehrmacht Enigma type I rotor the
bgneal@0:       // mapping is "EKMFLGDQVZNTOWYHXUSPAIBRCJ".
bgneal@0:       //
bgneal@0:       // ring_setting - this should be an integer from 0-25, inclusive, which
bgneal@0:       // indicates the Ringstellung. A value of 0 means there is no offset; e.g.
bgneal@0:       // the letter "A" is fixed to pin 0. A value of 1 means "B" is mapped to
bgneal@0:       // pin 0.
bgneal@0:       //
bgneal@0:       // stepping - this is the stepping or turnover parameter. It should be
bgneal@0:       // a string such as "Q". This will indicate that when the rotor transitions
bgneal@0:       // from "Q" to "R" (by observing the operator window), the rotor will "kick"
bgneal@0:       // the rotor to its left, causing it to rotate. If the rotor has more than one
bgneal@0:       // notch, a string of length 2 could be used, e.g. "ZM". Another way to think
bgneal@0:       // of this parameter is that when a character in the stepping string is visible
bgneal@0:       // in the operator window, a notch is lined up with the pawl on the left side
bgneal@0:       // of the rotor. This will allow the pawl to push up on the rotor *and* the
bgneal@0:       // rotor to the left when the next key is depressed.
bgneal@0:       //
bgneal@0:       // Note that for purposes of simulation, our rotors will always use
bgneal@0:       // alphabetic labels A-Z. In reality, the Heer & Luftwaffe devices used
bgneal@0:       // numbers 01-26, and Kriegsmarine devices used A-Z. Our usage of A-Z is
bgneal@0:       // simply for simulation convenience.
bgneal@0:       // display.
bgneal@0: 
bgneal@0:       rotor(const char* name, const char* wiring, int ring_setting = 0, const char* stepping = 0);
bgneal@0: 
bgneal@0:       // Returns the rotor name:
bgneal@0:       const std::string& name() const { return rotor_name; }
bgneal@0: 
bgneal@0:       // Spin the rotor such that the string val appears in the operator window:
bgneal@0:       void set_display(const char* val);
bgneal@0: 
bgneal@0:       // Returns what is currently being displayed in the operator window:
bgneal@0:       std::string get_display() const;
bgneal@0: 
bgneal@0:       // Simulate a signal entering the rotor from the right at a given pin:
bgneal@0:       // n must be an integer between 0 and 25.
bgneal@0:       // Returns the contact number of the output signal (0-25).
bgneal@0:       int signal_in(int n) const;
bgneal@0: 
bgneal@0:       // Simulate a signal entering the rotor from the left at a given contact position n.
bgneal@0:       // n must be an integer between 0 and 25.
bgneal@0:       // Returns the pin number of the output signal (0-25).
bgneal@0:       int signal_out(int n) const;
bgneal@0: 
bgneal@0:       // Return true if this rotor has a notch in the stepping position and false otherwise:
bgneal@0:       bool notch_over_pawl() const;
bgneal@0: 
bgneal@0:       // Rotate the rotor forward one step:
bgneal@0:       void rotate();
bgneal@0: 
bgneal@0:    private:
bgneal@0:       std::string rotor_name;
bgneal@0:       std::string wiring_str;
bgneal@0:       int ring_setting;
bgneal@0:       int pos;
bgneal@0:       int rotations;
bgneal@0:    };
bgneal@0: }
bgneal@0: 
bgneal@0: #endif