src/main.c


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#define NB_COLS 80
#define NB_ROWS 25
#define BPC     2
#define BPR     (BPC * NB_COLS)

#define VIDEO_BUFFER 0xB8000

/* XXX doest not always handle memory overlaps */
static void my_memmove(void *_dest, const void *_src, int n)
{
    char *dest = _dest;
    const char *src = _src;

    for (int i = 0; i < n; ++i) {
        dest[i] = src[i];
    }
}

static void my_memset(void *_dest, int c, int n)
{
    char *dest = _dest;

    for (int i = 0; i < n; ++i) {
        dest[i] = c;
    }
}

static void clear_line(void *_addr)
{
    char *addr = _addr;

    for (int i = 0; i < NB_COLS; ++i) {
        if (i % BPC == 0) {
            *addr++ = ' ';
        } else {
            *addr++ = 0x7;
        }
    }
}

int printk(const char *str)
{
    static const long int offset = VIDEO_BUFFER;
    static char *addr = (char *) VIDEO_BUFFER;
    int count = 0;

    for (int i = 0; str[i]; ++i) {
        /* TODO add the serial port handling */

        char chr;
        char *new_addr = addr;
        char *addr_line = (char *)(((long)(addr - offset) / BPR) * BPR) + offset;

        if ((long)addr >= offset + NB_ROWS * BPR) {
            /* shift up */
            addr -= BPR;
            addr_line -= BPR;
            my_memmove((void *)offset, (void *)offset + BPR, BPR * (NB_ROWS - 1));
            clear_line(addr_line);
        }


        switch (str[i]) {
            case '\n':
                new_addr = addr_line + BPR;
                chr = '\0';
                break;
            default:
                new_addr = addr + BPC;
                chr = str[i];
                break;
        }

        if (chr)
            *addr = chr;

        addr = new_addr;
        ++count;
    }

    return count;
}

int main(void)
{
}