kernel.c

#define MAX_ROWS 24

void handleInterrupt21( int ax, int bx, int cx, int dx );

void main()
{
    char line[80];
    int x;
   
    makeInterrupt21();
    interrupt( 33, 12, 2, 12, 0 );

    interrupt(33,0,"___.   .__                 __       .___           \r\n\0",0,0);
    interrupt(33,0,"\\_ |__ |  | _____    ____ |  | __ __| _/___  ______\r\n\0",0,0);
    interrupt(33,0," | __ \\|  | \\__  \\ _/ ___\\|  |/ // __ |/ _ \\/  ___/\r\n\0",0,0);
    interrupt(33,0," | \\_\\ \\  |__/ /\\ \\\\  \\___|    </ /_/ ( <_> )___ \\ \r\n\0",0,0);
    interrupt(33,0," |___  /____(____  /\\___  >__|_ \\____ |\\___/____  >\r\n\0",0,0);
    interrupt(33,0,"     \\/          \\/     \\/     \\/    \\/         \\/ \r\n\0",0,0);
    interrupt(33,0," V. 1.03, C. 2017. Based on a project by M. Black. \r\n\0",0,0);
    interrupt(33,0," Author(s): Sam Goodrick.\r\n\r\n\0",0,0);
   
    interrupt(33,0,"Hola mondo.\r\n\0",0,0);
    interrupt(33,0,"Enter a line: \0",0,0);
    interrupt(33,1,line,0,0);
    interrupt(33,0,"\r\nYou typed: \0",0,0);
    interrupt(33,0,line,0,0);
    interrupt(33,0,"\r\n\0",0,0);
    interrupt(33,0,"\rEnter a number: \0",0,0);
    interrupt(33,14,&x,0,0);
    interrupt(33,0,"\nYour number is \0",0,0);
    interrupt(33,13,x,0,0);
    interrupt(33,0,"\r\n\0",0,0);
    while(1);
}

void printString(char* c)
{
    int i = 0;
    char current;

    /* iterate char by char until the end of the string */
    do
    {
	current = *(c + i);
	/* interrupt 16 prints current character */
	interrupt( 16, 14*256+current, 0, 0, 0 );
	++i;
    }while( current != '\0' );
}

void readString(char* c)
{
    int i = 0;
    char current;
    
    do
    {
	/* interrupt 22 accepts a single keystroke and stores it in current */
	current = interrupt( 22, 0, 0, 0, 0 );
	/* print the inputted character with interrupt 16 */
	interrupt( 16, 14*256+current, 0, 0, 0 );
	*(c + i) = current;

	/* if BACKSPACE is pressed, decrement unless at beginning of string */
	if( current == 0x8 )
	{
	    if( i > 0 )
		--i;
	}
	else
	    ++i;
    } while( current != 0xD ); /*continue until ENTER is pressed */
    *(c + (i - 1)) = '\0';
}

void clearScreen(int bx, int cx)
{
    int i;
    for( i = 0; i < MAX_ROWS; ++i )
    {
    	interrupt( 33,0,"\r\n\0",0,0 );
    }

    /* reposition cursor in upperleft corner */
    interrupt( 16, 512, 0, 0, 0 );

    /* use interrupt 16 to set the colors of the terminal to bx and cx */
    if( bx > 0 && cx > 0 )
	interrupt( 16, 1536, 4096 * ( bx - 1 ) + 256 * ( cx - 1 ), 0, 6223 );

}

int mod(int a, int b)
{
    int x = a;
    while (x >= b) x = x - b;
    return x;
}

int div(int a, int b)
{
    int q = 0;
    while (q * b <= a) q++;
    return (q - 1);
}

void writeInt(int x)
{
    char number[6], *d;
    int q = x, r;
    if (x < 1)
    {
	d = number; *d = 0x30; d++; *d = 0x0; d--;
    }
    else
    {
	d = number + 5;
	*d = 0x0; d--;
	while (q > 0)
	{
	    r = mod(q,10); q = div(q,10);
	    *d = r + 48; d--;
	}
	d++;
    }
    interrupt(33,0,d,0,0);
}

void readInt(int* number)
{
    char* input;
    int i, digit, sum, len;

    /* read a string of digits and check it's length */
    interrupt( 33,1,input,0,0 );
    for( len = 0; *(input + len) != '\0'; ++len );

    sum = i = 0;
    
    while( *(input + i) != '\0' )
    {	
	/* subtract 48 to convert from ASCII to decimal */
	digit = *(input + i) - 48;

	/* convert each digit to its appropriate decimal place */
	sum += digit*pow( 10, len-1-i );
	++i;
    }
    *number = sum;
}

int pow( int b, int e )
{
    int result = 1;
    while (e)
    {
        if (e & 1)
            result *= b;
        e >>= 1;
        b *= b;
    }

    return result;
}

void handleInterrupt21( int ax, int bx, int cx, int dx )
{
    switch( ax )
    {
    case 0:
	printString( bx );
	break;
    case 1:
	readString( bx );
	break;
    case 12:
	clearScreen( bx, cx );
	break;
    case 13:
	writeInt( bx );
	break;
    case 14:
	readInt( bx );
	break;
    }
}