fix: not working with full board

src/main.c

@@ -12,25 +12,21 @@ int main(int argc, char **argv) {
 		0x010, 0x004, 0x000, 0x000, 0x040, 0x000, 0x000, 0x000, 0x000,
 		0x020, 0x000, 0x000, 0x001, 0x100, 0x010, 0x000, 0x000, 0x000,
 		0x000, 0x100, 0x080, 0x000, 0x000, 0x000, 0x000, 0x020, 0x000,
-		0x080, 0x000, 0x000, 0x000, 0x000, 0x000, 0x000, 0x000, 0x004,
-		0x008, 0x000, 0x000, 0x000, 0x000, 0x000, 0x000, 0x000, 0x001,
-		0x040, 0x000, 0x000, 0x000, 0x000, 0x000, 0x000, 0x000, 0x020,
+		0x080, 0x000, 0x000, 0x000, 0x020, 0x000, 0x000, 0x000, 0x004,
+		0x008, 0x000, 0x000, 0x080, 0x000, 0x004, 0x000, 0x000, 0x001,
+		0x040, 0x000, 0x000, 0x000, 0x002, 0x000, 0x000, 0x000, 0x020,
 		0x000, 0x020, 0x000, 0x000, 0x000, 0x000, 0x002, 0x080, 0x000,
 		0x000, 0x000, 0x000, 0x008, 0x001, 0x100, 0x000, 0x000, 0x010,
 		0x000, 0x000, 0x000, 0x000, 0x080, 0x000, 0x000, 0x040, 0x100,
 		// clang-format on
 	};
+	sudoku_init(board);
 	sudoku_print(board);
+
+	for (int i = 0; i < 2; i++) {
 		sudoku_solve_step(board);
 		sudoku_print(board);
-	sudoku_solve_step(board);
-	sudoku_print(board);
-	sudoku_solve_step(board);
-	sudoku_print(board);
-	sudoku_solve_step(board);
-	sudoku_print(board);
-	sudoku_solve_step(board);
-	sudoku_print(board);
+	}
 
 	return EXIT_SUCCESS;
 }

src/sudoku.c

@@ -8,6 +8,12 @@
 
 #include "util/intdef.h"
 
+void sudoku_init(u16 *board) {
+	for (uint i = 0; i < SUDOKU_LEN; i++) {
+		board[i] |= SUDOKU_ALL & -!board[i];
+	}
+}
+
 /* removes `val` from `*brd`, if `*brd` is not equal to `val` */
 static inline void setbrdpos(u16 *brd, u16 val) {
 	*brd &= ~(val & -(*brd != val));
@@ -29,8 +35,6 @@ void sudoku_place(u16 *brd, u16 val, uint idx) {
 
 void sudoku_solve_step(u16 *board) {
 	for (uint i = 0; i < SUDOKU_LEN; i++) {
-		board[i] |= SUDOKU_ALL & -!board[i];
-
 		switch (board[i]) {
 		case SUDOKU_1:
 		case SUDOKU_2:
@@ -42,6 +46,7 @@ void sudoku_solve_step(u16 *board) {
 		case SUDOKU_8:
 		case SUDOKU_9:
 			sudoku_place(board, board[i], i);
+			// printf("%i,%i\n", i % SUDOKU_DPT, i / SUDOKU_DPT);
 		}
 	}
 }
@@ -51,7 +56,7 @@ void sudoku_print(const u16 *board) {
 	for (uint i = 0; i < SUDOKU_LEN; i++) {
 		char tile;
 		switch (board[i]) {
-		case 0:        tile = 'x'; break;
+		// case 0:        tile = 'x'; break;
 		case SUDOKU_1: tile = '1'; break;
 		case SUDOKU_2: tile = '2'; break;
 		case SUDOKU_3: tile = '3'; break;
@@ -65,7 +70,7 @@ void sudoku_print(const u16 *board) {
 		};
 
 		printf("| %c ", tile);
-		// printf("|%3i", board[i]);
+		// printf("|%3X", board[i]);
 		if (i % 9 == 8) printf("|\n");
 	}
 	printf("+———-———-———-———-———-———-———-———-———+\n");

src/sudoku.h

@@ -22,6 +22,9 @@ enum sudoku_bitmask {
 	SUDOKU_ALL = 0x01FF,
 };
 
+/* 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);