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1 // Copyright (C) 2012 by Brian Neal.
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2 // This file is part of Cpp-Enigma, the Enigma Machine simulation.
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3 // Cpp-Enigma is released under the MIT License (see License.txt).
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4 //
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5 // rotor.cpp - Implementation file for the rotor class.
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6
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7 #include <set>
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8 #include <array>
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9 #include <algorithm>
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10 #include "rotor.h"
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11 #include "enigma_utils.h"
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12
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13 using namespace enigma;
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14
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15 ////////////////////////////////////////////////////////////////////////////////
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16
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17 namespace
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18 {
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19 const char* const ucase = "ABCDEFGHIJKLMNOPQRSTUVWXYZ";
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20
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21 // Turned into a function to avoid translation unit initialization order problems.
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22 const std::set<char>& get_ucase_set()
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23 {
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24 static const std::set<char> the_set(ucase, ucase + 26);
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25 return the_set;
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26 }
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27 }
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28
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29 ////////////////////////////////////////////////////////////////////////////////
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30
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31 rotor::rotor(const char* name, const char* wiring, int ring_setting, const char* stepping)
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32 : rotor_name{name},
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33 wiring_str{wiring},
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34 ring_setting{ring_setting},
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35 pos{0},
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36 display_val{'A'},
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37 entry_map(),
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38 exit_map(),
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39 display_map(),
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40 pos_map(),
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41 step_map()
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42 {
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43 // check wiring length
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44 if (wiring_str.size() != 26)
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45 {
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46 throw rotor_error("invalid wiring length");
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47 }
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48
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49 // ensure wiring contains only uppercase letters & every char must appear
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50 // exactly once:
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51 const std::set<char>& ucase_set(get_ucase_set());
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52
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53 // g++ 4.6.3 warns about missing braces unless we double them up, below:
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54 std::array<int, 26> letter_counts = {{ 0 }};
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55 for (int i = 0; i < 26; ++i)
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56 {
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57 const char c{wiring_str[i]};
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58 if (ucase_set.find(c) == ucase_set.end())
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59 {
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60 throw rotor_error("invalid wiring");
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61 }
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62 ++letter_counts[c - 'A'];
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63 }
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64
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65 if (std::find_if(letter_counts.begin(),
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66 letter_counts.end(),
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67 [](int n) { return n != 1; }) != letter_counts.end())
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68 {
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69 throw rotor_error("invalid wiring; duplicate letter");
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70 }
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71
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72 if (ring_setting < 0 || ring_setting >= 26)
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73 {
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74 throw rotor_error("invalid ring setting");
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75 }
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76 set_ring_setting(ring_setting);
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77
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78 // Initialize our two arrays that describe the internal wiring. Arrays are used
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79 // to do fast lookup from both entry (from the right) and exit (from the
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80 // left).
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81
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82 for (int i = 0; i < 26; ++i)
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83 {
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84 const int v = wiring_str[i] - 'A';
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85 entry_map[i] = v;
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86 exit_map[v] = i;
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87 }
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88
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89 // Build a lookup table that tells us when the pawls are allowed to step.
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90 // The index to this array is the current display letter [A-Z] - 'A'.
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91
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92 if (stepping != nullptr)
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93 {
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94 for (char c = *stepping; *stepping != '\0'; ++stepping)
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95 {
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96 if (ucase_set.find(c) != ucase_set.end())
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97 {
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98 step_map[c - 'A'] = true;
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99 }
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100 else
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101 {
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102 throw rotor_error("invalid stepping");
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103 }
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104 }
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105 }
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106
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107 // set initial position
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108 set_display('A');
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109 }
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110
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111 ////////////////////////////////////////////////////////////////////////////////
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112
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113 void rotor::set_ring_setting(int n)
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114 {
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115 ring_setting = n;
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116
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117 // Build a mapping from window display values to positions
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118 // and a reverse mapping of position to display value:
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119 for (int i = 0; i < 26; ++i)
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120 {
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121 const int n = alpha_mod(i - ring_setting);
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122 display_map[i] = n;
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123 pos_map[n] = i + 'A';
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124 }
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125 }
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