void zero_fb(x1, y1, x2, y2) {
void zero_fb(int x1, int y1, int x2, int y2) {
void zero_fb(x1, y1, x2, y2) {	int pixelsize = bpp >> 3;	int line, fill = 0;	char *dst;		if (x1 < 0 || x2 <= x1 || x2 > dpy_x) {		return;	}	if (y1 < 0 || y2 <= y1 || y2 > dpy_y) {		return;	}	dst = main_fb + y1 * main_bytes_per_line + x1 * pixelsize;	line = y1;	while (line++ < y2) {		memset(dst, fill, (size_t) (x2 - x1) * pixelsize);		dst += main_bytes_per_line;	}}