@@ -61,28 +61,34 @@ Maze hunt_and_kill(int w, int h, unsigned seed, C callback = [](Maze &){})

     auto done = false;

     while (!done)

     {

+        #define FOR_NEIGHBOR(...) \

+            for (auto i = 0; i < 4; ++i) \

+            { \

+                auto ni = i%2*4-2;   /* -2, +2, -2, +2 */ \

+                auto nx = ni* (i/2); /*  0,  0, -2, +2 */ \

+                auto ny = ni*!(i/2); /* -2, +2,  0,  0 */ \

+                __VA_ARGS__ \

+            }

         // Call callback.

         callback(maze);

         // Find number of neighbors.

         auto n = 0;

-        for (auto ny = -2; ny <= 2; ny += 2)

-        for (auto nx = -2; nx <= 2; nx += 2)

-            if (!nx != !ny)

+        FOR_NEIGHBOR(

             if (maze(cx+nx, cy+ny) == Maze::WALL)

                 ++n;

+        )

         // If we have neighbors, carve path to random one.

         if (n != 0)

         {

             n = std::rand() % n;

-            for (auto ny = -2; ny <= 2; ny += 2)

-            for (auto nx = -2; nx <= 2; nx += 2)

-                if (!nx != !ny)

+            FOR_NEIGHBOR(

                 if (maze(cx+nx, cy+ny) == Maze::WALL && n-- == 0)

                 {

                     maze(cx+nx/2, cy+ny/2) = maze(cx+nx, cy+ny) = Maze::PATH;

                     cx = cx+nx;

                     cy = cy+ny;

                 }

+            )

             continue;

         }

         // No neighbors, done unless there's an uncarved cell to restart at.

@@ -90,17 +96,17 @@ Maze hunt_and_kill(int w, int h, unsigned seed, C callback = [](Maze &){})

             for (; ry < h; ry += 2, rx = 1)

             for (; rx < w; rx += 2)

                 if (maze(rx, ry) == Maze::WALL)

-                    for (auto ny = -2; ny <= 2; ny += 2)

-                    for (auto nx = -2; nx <= 2; nx += 2)

-                        if (!nx != !ny)

+                    FOR_NEIGHBOR(

                         if (maze(rx+nx, ry+ny) == Maze::PATH)

                         {

                             cx = rx+nx;

                             cy = ry+ny;

                             return false;

                         }

+                    )

             return true;

         }();

+        #undef FOR_NEIGHBOR

     }

     // Exit.

     w -= (w + 1) % 2;