wrote documentation for sudoku_print and sudoku_solve_step

src/sudoku.c

@@ -8,11 +8,38 @@
 
 #include "util/intdef.h"
 
+void sudoku_init(u16 *board) {
+	for (uint i = 0; i < SUDOKU_DEPTH_2; i++) {
+		board[i] |= SUDOKU_ALL & -!board[i];
+	}
+}
+
+void sudoku_place(u16 *board, u16 val, uint idx) {
+	uint icol = idx % SUDOKU_DEPTH;
+	uint irow = idx - icol;
+	uint ibox = idx - (idx % SUDOKU_DEPTH_SQRT);
+	for (uint i = 0; i < SUDOKU_DEPTH; i++) {
+		board[irow + i] &= ~val;
+		board[icol + (i * SUDOKU_DEPTH)] &= ~val;
+		board[ibox + (i / SUDOKU_DEPTH_SQRT * SUDOKU_DEPTH) + (i % SUDOKU_DEPTH_SQRT)] &= ~val;
+	}
+}
+
 void sudoku_solve_step(u16 *board) {
-	u16 bmask[SUDOKU_DEPTH_2]; // board mask
-	memcpy(bmask, board, SUDOKU_DEPTH_2 * 2);
-	// TODO: first, we must somehow loop through the columns
-	// TODO: then, we must write to the bmask or do *magic* for the bits designating to 1-9 to be unset if ONLY one of them is set
+	for (uint i = 0; i < SUDOKU_DEPTH_2; i++) {
+		switch (board[i]) {
+		case SUDOKU_1:
+		case SUDOKU_2:
+		case SUDOKU_3:
+		case SUDOKU_4:
+		case SUDOKU_5:
+		case SUDOKU_6:
+		case SUDOKU_7:
+		case SUDOKU_8:
+		case SUDOKU_9:
+			sudoku_place(board, board[i], i);
+		}
+	}
 }
 
 void sudoku_print(const u16 *board) {

src/sudoku.h

@@ -4,8 +4,9 @@
 
 #include "util/intdef.h"
 
-#define SUDOKU_DEPTH   9                             // defines the "depth" of the puzzle.
-#define SUDOKU_DEPTH_2 (SUDOKU_DEPTH * SUDOKU_DEPTH) // computes how many squares there are
+#define SUDOKU_DEPTH_SQRT 3
+#define SUDOKU_DEPTH      (SUDOKU_DEPTH_SQRT * SUDOKU_DEPTH_SQRT)
+#define SUDOKU_DEPTH_2    (SUDOKU_DEPTH * SUDOKU_DEPTH)
 
 /* bitmask  */
 enum sudoku_bitmask {
@@ -18,10 +19,17 @@ enum sudoku_bitmask {
 	SUDOKU_7 = 0x040,
 	SUDOKU_8 = 0x080,
 	SUDOKU_9 = 0x100,
+	SUDOKU_ALL = 0x01FF,
 };
 
-/* TODO: write documentation */
+/* initialises the sudoku board to `SUDOKU_ALL`. (if the tile is empty) */
+void sudoku_init(u16 *board);
+
+/* places `val` at `idx` in `board`, and removes `val` from the possibilities in neighbouring tiles */
+void sudoku_place(u16 *board, u16 val, uint idx);
+
+/* loops through the board, updating all places that only have a single possibility set. */
 void sudoku_solve_step(u16 *board);
 
-/* TODO: write documentation */
+/* prints the sudoku board to `stdout` */
 void sudoku_print(const u16 *board);