bootsector_tictactoe/boot.c

#include <stdbool.h>

#define BOARD ((Cell*)0x7F00)

typedef enum : char {
	NONE  = ' ',
	CROSS = 'X',
	NOT   = 'O'
} Cell;

inline void putchar(char);
inline char readchar(void);
inline void printboard(void);
inline bool checkwin(Cell c);

void _start(void) {
	Cell cur = CROSS;
	for (char i = 0; i < 3; i++)
		for (char j = 0; j < 3; j++)
			*(BOARD + i * 3 + j) = NONE;
	while (1) {
		printboard();
		char c;
		switch (readchar()) {
			case 0x47: // 7
				c = 0;
				break;
			case 0x48: // 8
				c = 1;
				break;
			case 0x49: // 9
				c = 2;
				break;

			case 0x4B: // 4
				c = 3;
				break;
			case 0x4C: // 5
				c = 4;
				break;
			case 0x4D: // 6
				c = 5;
				break;

			case 0x4F: // 1
				c = 6;
				break;
			case 0x50: // 2
				c = 7;
				break;
			case 0x51: // 3
				c = 8;
				break;
			default:
				continue;
		}
		if (*(BOARD + c) != NONE)
			continue;
		*(BOARD + c) = cur;
		if (checkwin(cur))
			break;
		if (cur == CROSS)
			cur = NOT;
		else
			cur = CROSS;
	}
	putchar(cur);
	printboard();
	while(1)
		;
}

inline void printboard(void) {
	__asm__ volatile (
		"movb $0x02, %%ah;"
		"movb $0x00, %%bh;"
		"movw $0x0000, %%dx;"
		"int $0x10;"
		:
		:
		:"%ah","%bh","%dx"
	);
	for (char i = 0; i < 3; i++) {
		for (char j = 0; j < 3; j++) {
			putchar(*(BOARD + i * 3 + j));
		}
		putchar('\n');
		putchar('\r');
	}
}

inline bool checkwin(Cell c) {
	for (char i = 0; i < 3; i++)
		if ((*(BOARD + i) == c) && (*(BOARD + i + 3) == c) && (*(BOARD + i + 6) == c))
			return true;
	for (char i = 0; i < 3; i++)
		if ((*(BOARD + 3*i) == c) && (*(BOARD + 3*i + 1) == c) && (*(BOARD + 3*i + 2) == c))
			return true;
	if (*(BOARD) == c && *(BOARD + 4) == c && *(BOARD + 8))
		return true;
	if (*(BOARD + 2) == c && *(BOARD + 4) == c && *(BOARD + 7))
		return true;
	return false;
}

inline char readchar(void) {
	char out;
__asm__ volatile (
	"movb $0x00, %%ah;"
	"int $0x16;"
	"movb %%ah, %0;"
	:"=r"(out)
	:
	:"%ax"
);
	return out;
}

inline void putchar(char out) {
__asm__ volatile (
	"movb $0x0e, %%ah;"
	"movb %0, %%al;"
	"int $0x10;"
	:
	:"r"(out)
	:"%ax"
);
}