Update README to remove optimizations section

README.md

@@ -45,7 +45,8 @@ the aforementioned specifications.
 ## Optimization
 An optimization directive has been included in `board.c` to allow for the near
 complete removal of boundary checks and error conditions. To enable this
-optimization, simply add `-DOPTIMIZE` to your compiler flags.
+optimization, simply add `-DOPTIMIZE` to your compiler flags. For insane speeds,
+don't forget the `-O3` gcc flag.
 
 ## Live status output
 If you would like to get a live status output of speculative value placement,
@@ -56,14 +57,6 @@ are really only useful on much slower devices.
 
 ## TODO
 
-* Optimizations
-
-  * Packed structures
-
-  * Better structure layouts
-
-  * Optimize speculative value placement error-condition checks
-
 * Cleaner code
 
   * Move printing to separate file

board.c

@@ -72,6 +72,37 @@ meta_init (struct metadata *meta)
 }
 
 
+void
+board_make_links (struct board *board)
+{
+  for (board_pos y = 0; y < 9; ++y)
+    for (board_pos x = 0; x < 9; ++x)
+    {
+      unsigned pos = ELEM_POS (x, y);
+
+      unsigned link_count = -1;
+
+      /* Link column adjacents */
+      for (board_pos lx = 0; lx < 9; ++lx)
+        if (lx != x)
+          board->links[pos][++link_count] = BOARD_ELEM (board, lx, y);
+
+      /* Link column adjacents */
+      for (board_pos ly = 0; ly < 9; ++ly)
+        if (ly != y)
+          board->links[pos][++link_count] = BOARD_ELEM (board, x, ly);
+
+      /* Link quadrant adjacents */
+      board_pos qx = TO_QUAD (x);
+      board_pos qy = TO_QUAD (y);
+      for (board_pos lqy = 0; lqy < 3; ++lqy)
+        for (board_pos lqx = 0; lqx < 3; ++lqx)
+          if ((lqx + qx) != x && (lqy + qy) != y)
+            board->links[pos][++link_count] = BOARD_ELEM (board, lqx + qx, lqy + qy);
+    }
+}
+
+
 void
 board_init (struct board *board)
 {
@@ -80,8 +111,17 @@ board_init (struct board *board)
   defval.potential = 0x1FF;
   defval.complexity = 9;
 
-  for (size_t t = 0; t < (sizeof (board->elements) / sizeof (struct board_element)); ++t)
-    memcpy (&board->elements[t], &defval, sizeof (struct board_element));
+  for (board_pos y = 0; y < 9; ++y)
+    for (board_pos x = 0; x < 9; ++x)
+    {
+      struct board_element *elem = BOARD_ELEM (board, x, y);
+
+      /* Set default state */
+      memcpy (elem, &defval, sizeof (struct board_element));
+    }
+
+
+  board_make_links (board);
 
   board->complexity = 9;
   
@@ -224,6 +264,7 @@ board_set (
     );
 
     struct board_element *elem = BOARD_ELEM (board, x, y);
+    
     elem->has_value = true;
     elem->value = value;
   }
@@ -257,7 +298,7 @@ board_mark (
 }
 
 
-void 
+bool 
 board_unmark (
   struct board *board,
   board_pos x,
@@ -272,19 +313,29 @@ board_unmark (
       "Attempt to mark element with value"
     );
 
-    struct board_element *elem = BOARD_ELEM (board, x, y);
-
-    if (board_is_marked (board, x, y, value))
-    {
-      /* Shift bit to correct place and then invert first 9 bits */
-      elem->potential ^= (1 << value);
-      --(elem->complexity);
-    }
+    return elem_unmark (BOARD_ELEM (board, x, y), value);
   }
   else ERROR("Invalid parameters to function board_unmark()");
 }
 
 
+bool
+elem_unmark (
+  struct board_element *elem,
+  element_value value
+)
+{
+  if (elem_is_marked (elem, value))
+  {
+    /* Shift bit to correct place and then invert first 9 bits */
+    elem->potential ^= (1 << value);
+    --(elem->complexity);
+  }
+
+  return elem->potential != 0;
+}
+
+
 bool
 board_has_value (
   const struct board *board,
@@ -325,12 +376,22 @@ board_is_marked (
 {
   if (is_in_bounds (x, y) && is_valid_value (value))
   {
-    return BOARD_ELEM (board, x, y)->potential & (1 << value);
+    return elem_is_marked(BOARD_ELEM (board, x, y), value);
   }
   else ERROR("Invalid parameters to function board_is_marked()");
 }
 
 
+bool
+elem_is_marked (
+  const struct board_element *elem,
+  element_value value
+)
+{
+  return elem->potential & (1 << value);
+}
+
+
 bool
 board_is_valid (struct board *board)
 {
@@ -524,32 +585,17 @@ board_place (
   {
     if (board_meta_can_set (board, x, y, value))
     {
-      /* Unmark x-axis */
-      for (board_pos unmark_x = 0; unmark_x < 9; ++unmark_x)
-        if (unmark_x != x && ! board_has_value (board, unmark_x, y))
-          board_unmark (board, unmark_x, y, value);
+      unsigned pos = ELEM_POS (x, y);
 
-      /* Unmark y-axis */
-      for (board_pos unmark_y = 0; unmark_y < 9; ++unmark_y)
-        if (unmark_y != y && ! board_has_value (board, x, unmark_y))
-          board_unmark (board, x, unmark_y, value);
-
-      /* Update quad */
-      board_pos quad_x = TO_QUAD (x);
-      board_pos quad_y = TO_QUAD (y);
-
-      for (board_pos unmark_y = 0; unmark_y < 3; ++unmark_y)
-        for (board_pos unmark_x = 0; unmark_x < 3; ++unmark_x)
+      /* Unmark all adjacent elements */
+      for (unsigned i = 0; i < 20; ++i)
+        if (
+          ! board->links[pos][i]->has_value &&
+          ! elem_unmark (board->links[pos][i], value)
+        )
         {
-          board_pos target_x = quad_x + unmark_x;
-          board_pos target_y = quad_y + unmark_y;
-
-          /* Unmark value for all unset elements in quad */
-          if (
-              (target_x != x || target_y != y) &&
-              !board_has_value (board, target_x, target_y)
-          )
-            board_unmark (board, target_x, target_y, value);
+          /* Unmarking potential caused element to have no potential */
+          return false;
         }
 
       /* Set value */
@@ -585,7 +631,7 @@ board_place_speculative (
       /* Create duplicate and place value */
       board_copy (board, board_duplicate);
 
-      if (! board_place (board_duplicate, x, y, value) || ! board_is_valid (board_duplicate))
+      if (! board_place (board_duplicate, x, y, value))
         return NULL;
 
       board_refresh_complexity (board_duplicate);
@@ -632,5 +678,10 @@ board_refresh_complexity (struct board *board)
 void
 board_copy (const struct board *board_from, struct board *board_to)
 {
-  memcpy (board_to, board_from, sizeof(struct board));
+  /* Copy everything except the links */
+  memcpy (
+      board_to,
+      board_from,
+      sizeof(struct board) - sizeof (((struct board *)0)->links)
+  );
 }

board.h

@@ -6,10 +6,13 @@
 
 #include <stdbool.h>
 
+
+#define ELEM_POS(x, y) (((y) * 9) + (x))
+
 /**
  * Get a `struct board_element`-entry from a specified location on the board
  */
-#define BOARD_ELEM(board_ptr, x, y) (&(board_ptr)->elements[((y) * 9) + (x)])
+#define BOARD_ELEM(board_ptr, x, y) (&(board_ptr)->elements[ELEM_POS (x, y)])
 
 /**
  * Get a `struct metadata`-entry from a specified location on the quadrand grid
@@ -32,6 +35,8 @@
  */
 #define TO_QUAD(pos) (((pos) / 3) * 3)
 
+struct board_element;
+
 typedef unsigned short int board_pos;
 typedef unsigned char element_value;
 
@@ -45,13 +50,9 @@ typedef unsigned char element_value;
 struct board_element {
   bool has_value : 1;                 /* Whether element has a decided value */
 
-  union {
-    element_value    value      : 4;  /* Value of element */
-    struct {
-      unsigned short potential  : 9;  /* Bitfield of possible values */
-      unsigned char  complexity : 4;  /* Complexity tracker */
-    };
-  };
+  element_value value : 4;            /* Value of element */
+  unsigned short potential : 9;       /* Bitfield of possible values*/
+  unsigned char complexity : 4;       /* Complexity tracker */
 };
 
 /**
@@ -80,6 +81,9 @@ struct board {
   struct metadata meta_quad [9];      /* Quadrant metadata */
   struct metadata meta_row  [9];      /* Row metadata */
   struct metadata meta_col  [9];      /* Column metadata */
+
+
+  struct board_element *links [81][20];/* All "connected", "adjacent" elements */
 };
 
 
@@ -90,6 +94,13 @@ void
 meta_init (struct metadata *meta);
 
 
+/*
+ * Just generate board element adjacency links
+ */
+void
+board_make_links (struct board *board);
+
+
 /**
  * Initialize a board to a blank state with maximum complexity
  */
@@ -184,7 +195,7 @@ board_mark (
  *
  * NOTE: Unmarking an element with a decied value is undefined
  */
-void
+bool
 board_unmark (
   struct board *board,
   board_pos x,
@@ -193,6 +204,16 @@ board_unmark (
 );
 
 
+/**
+ * Removes a marking of a potential value of an element
+ */
+bool
+elem_unmark (
+  struct board_element *elem,
+  element_value value
+);
+
+
 /**
  * Get whether or not an element has a decided value
  */
@@ -231,6 +252,16 @@ board_is_marked (
 );
 
 
+/**
+ * Get whether or not a given element is marked with a particular value
+ */
+bool
+elem_is_marked (
+  const struct board_element *elem,
+  element_value value
+);
+
+
 /**
  * Checks if there are any pairs of board elements that share a value and
  * also share either a row or a column

main.c

@@ -64,7 +64,10 @@ tables_ensure_depth (struct boards_table *board_spec, unsigned long long depth)
 
     /* Allocate boards */
     for (unsigned long long l = board_spec->max_depth; l < new_max; ++l)
+    {
       board_spec->board_specs[l] = malloc (sizeof (struct board));
+      board_make_links (board_spec->board_specs[l]);
+    }
 
     /* Update max depth */
     board_spec->max_depth = new_max;
@@ -316,6 +319,13 @@ first_potential_value (struct board_element *element, struct board *board, bool
 /**
  * Reduce away all elements on board with complexity=1 until none remain
  */
+#ifdef NOVERB
+bool
+simplify (
+  struct boards_table *board_specs,
+  unsigned long long depth
+)
+#else
 bool
 simplify (
   struct boards_table *board_specs,
@@ -323,10 +333,12 @@ simplify (
   unsigned long long *counter,
   unsigned verbosity
 )
+#endif
 {
   /* Get current table */
   struct board *board = board_specs->board_specs[depth];
 
+#ifndef NOVERB
   if (verbosity > 0)
   {
     if (((*counter) & (0xFFFF >> (4 * (4 - verbosity)))) == 0)
@@ -337,6 +349,7 @@ simplify (
     }
     *counter += 1;
   }
+#endif
 
 
   bool error;
@@ -358,15 +371,8 @@ simplify (
 
             ++count;
 
-            //fprintf (stderr, "Placing (%u, %u)=%u (potential=%u)\n", x, y, value, elem->potential);
-            
             if (! board_place (board, x, y, value))
-            {
-              bool rerr = meta_has_value (BOARD_ROW (board, y), value);
-              bool cerr = meta_has_value (BOARD_COL (board, x), value);
-              bool qerr = meta_has_value (BOARD_QUAD (board, TO_QUAD (x), TO_QUAD (y)), value);
-              fprintf (stderr, "Error (%u, %u, %u)\n", rerr, cerr, qerr);
-            }
+              return false;
           }
         }
 
@@ -382,14 +388,14 @@ simplify (
         struct board_element *elem = BOARD_ELEM (board, x, y);
         /* Find a simplest element on the board */
         if (
-            ! board_has_value (board, x, y) &&
+            ! elem->has_value &&
             elem->complexity == board->complexity
         )
           for (element_value value = 0; value < 9; ++value)
           {
             /* Try speculative placement of each potential value and recurse */
             tables_ensure_depth (board_specs, depth + 1);
-            if ((elem->potential & (1 << value)) != 0)
+            if (elem_is_marked (elem, value))
             {
               struct board *board_spec =
                 board_place_speculative (
@@ -403,18 +409,27 @@ simplify (
               /* If speculative placement failed, try another value */
               if (board_spec == NULL)
               {
-                board_unmark (board, x, y, value);
+                if (! elem_unmark (elem, value))
+                  return false;
                 continue;
               }
 
               /* Found solution */
+
               if (
+#ifdef NOVERB
+                  simplify (
+                    board_specs,
+                    depth + 1
+                  ) &&
+#else
                   simplify (
                     board_specs,
                     depth + 1,
                     counter,
                     verbosity
                   ) &&
+#endif
                   board_spec->complexity == 0)
               {
                 board_copy (board_spec, board);
@@ -422,7 +437,8 @@ simplify (
                 y = 9;
                 value = 9;
               }
-              else board_unmark (board, x, y, value);
+              else if (! elem_unmark (elem, value))
+                return false;
             }
           }
       }