--- a/enigma/rotor.cpp	Thu Jun 21 21:05:26 2012 -0500
+++ b/enigma/rotor.cpp	Fri Jun 22 20:15:11 2012 -0500
@@ -8,21 +8,37 @@
 #include <array>
 #include <algorithm>
 #include "rotor.h"
+#include "enigma_utils.h"
 
 using namespace enigma;
 
+////////////////////////////////////////////////////////////////////////////////
+
 namespace
 {
    const char* const ucase = "ABCDEFGHIJKLMNOPQRSTUVWXYZ";
-   const std::set<char> ucase_set(ucase, ucase + 26);
+
+   // Turned into a function to avoid translation unit initialization order problems.
+   const std::set<char>& get_ucase_set()
+   {
+      static const std::set<char> the_set(ucase, ucase + 26);
+      return the_set;
+   }
 }
 
+////////////////////////////////////////////////////////////////////////////////
+
 rotor::rotor(const char* name, const char* wiring, int ring_setting, const char* stepping)
- : rotor_name(name),
-   wiring_str(wiring),
-   ring_setting(ring_setting),
-   pos(0),
-   rotations(0)
+ : rotor_name{name},
+   wiring_str{wiring},
+   ring_setting{ring_setting},
+   pos{0},
+   display_val{'A'},
+   entry_map(),
+   exit_map(),
+   display_map(),
+   pos_map(),
+   step_map()
 {
    // check wiring length
    if (wiring_str.size() != 26)
@@ -32,12 +48,13 @@
 
    // ensure wiring contains only uppercase letters & every char must appear
    // exactly once:
+   const std::set<char>& ucase_set(get_ucase_set());
 
-   std::array<int, 26> letter_counts {{ 0 }};
+   // g++ 4.6.3 warns about missing braces unless we double them up, below:
+   std::array<int, 26> letter_counts = {{ 0 }};
    for (int i = 0; i < 26; ++i)
    {
-      const char c(wiring_str[i]);
-
+      const char c{wiring_str[i]};
       if (ucase_set.find(c) == ucase_set.end())
       {
          throw rotor_error("invalid wiring");
@@ -51,4 +68,58 @@
    {
       throw rotor_error("invalid wiring; duplicate letter");
    }
+
+   if (ring_setting < 0 || ring_setting >= 26)
+   {
+      throw rotor_error("invalid ring setting");
+   }
+   set_ring_setting(ring_setting);
+
+   // Initialize our two arrays that describe the internal wiring. Arrays are used
+   // to do fast lookup from both entry (from the right) and exit (from the
+   // left).
+
+   for (int i = 0; i < 26; ++i)
+   {
+      const int v = wiring_str[i] - 'A';
+      entry_map[i] = v;
+      exit_map[v] = i;
+   }
+
+   // Build a lookup table that tells us when the pawls are allowed to step.
+   // The index to this array is the current display letter [A-Z] - 'A'.
+
+   if (stepping != nullptr)
+   {
+      for (char c = *stepping; *stepping != '\0'; ++stepping)
+      {
+         if (ucase_set.find(c) != ucase_set.end())
+         {
+            step_map[c - 'A'] = true;
+         }
+         else
+         {
+            throw rotor_error("invalid stepping");
+         }
+      }
+   }
+
+   // set initial position
+   set_display('A');
 }
+
+////////////////////////////////////////////////////////////////////////////////
+
+void rotor::set_ring_setting(int n)
+{
+   ring_setting = n;
+
+   // Build a mapping from window display values to positions
+   // and a reverse mapping of position to display value:
+   for (int i = 0; i < 26; ++i)
+   {
+      const int n = alpha_mod(i - ring_setting);
+      display_map[i] = n;
+      pos_map[n] = i + 'A';
+   }
+}