diff --git a/boot.c b/boot.c
index 273e672..d49b3ad 100644
--- a/boot.c
+++ b/boot.c
@@ -8,7 +8,7 @@ typedef enum : char {
 	NOT   = 'O'
 } Cell;
 
-Cell* board = ((Cell*)0x7F00);
+Cell* const board = (Cell*)0x7F00;
 
 HEDLEY_ALWAYS_INLINE char readchar(void);
 HEDLEY_ALWAYS_INLINE bool checkwin(Cell c);
@@ -24,9 +24,8 @@ void _start(void) {
 	"start:\n"
 	);
 	Cell cur = CROSS;
-	for (char i = 0; i < 3; i++)
-		for (char j = 0; j < 3; j++)
-			board[i * 3 + j] = NONE;
+	for (unsigned char i = 0; i < 9; i++)
+		board[i] = NONE;
 	while (1) {
 		printboard();
 		char k = readchar();
@@ -45,10 +44,7 @@ void _start(void) {
 		board[c] = cur;
 		if (checkwin(cur))
 			break;
-		if (cur == CROSS)
-			cur = NOT;
-		else
-			cur = CROSS;
+		cur ^= (CROSS ^ NOT);
 	}
 	putchar(cur);
 	printboard();
@@ -83,10 +79,8 @@ void printboard(void) {
 HEDLEY_ALWAYS_INLINE
 bool checkwin(Cell c) {
 	for (size_t i = 0; i <= 2; i++)
-		if ((board[i] == c) && (board[i + 3] == c) && (board[i + 6] == c))
-			return true;
-	for (size_t i = 0; i <= 2; i++)
-		if ((board[3*i] == c) && (board[3*i + 1] == c) && (board[3*i + 2] == c))
+		if (((board[i] == c) && (board[i + 3] == c) && (board[i + 6] == c)) &&
+		   ((board[3*i] == c) && (board[3*i + 1] == c) && (board[3*i + 2] == c)))
 			return true;
 	if (board[0] == c && board[4] == c && board[8] == c)
 		return true;