bootsector_tictactoe/boot.c

#include <stdlib.h>
#include <stdbool.h>
#include "hedley.h"

#define BOARD ((Cell*)0x7F00)

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

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

char numpadkeys[];

void _start(void) {
	__asm__ volatile (
		"movl $0x8000, %esp\n"
		"ljmp $(0),$(start)\n"
	"start:\n"
	);
	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 k = readchar();
		char o;
		if      (k > 0x46)
			o = 0x47;
		else if (k < 0x13)
			o =  0x10;
		else if (k < 0x21)
			o = (0x1E - 4);
		else
			o = (0x2C - 8);
		size_t c = numpadkeys[k - o];
		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)
		;
	HEDLEY_UNREACHABLE();
}
// numpadkeys[x - 0x47]
char numpadkeys[] = {0, 1, 2, false, 3, 4, 5, false, 6, 7, 8};


HEDLEY_NEVER_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');
	}
}

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))
			return true;
	if (BOARD[0] == c && BOARD[4] == c && BOARD[8] == c)
		return true;
	if (BOARD[2] == c && BOARD[4] == c && BOARD[6] == c)
		return true;
	return false;
}
/*
 * 012
 * 345
 * 678
 */

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

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