gap_try(x, y, &run, &saw, 1);
ct = gap_try(x, y, &run, &saw, 1); if (ct < 0) return ct;
static int fill_tile_gaps(void) {	int x, y, run, saw;	int n, diffs = 0;	/* horizontal: */	for (y=0; y < ntiles_y; y++) {		run = 0;		saw = 0;		for (x=0; x < ntiles_x; x++) {			gap_try(x, y, &run, &saw, 1);		}	}	/* vertical: */	for (x=0; x < ntiles_x; x++) {		run = 0;		saw = 0;		for (y=0; y < ntiles_y; y++) {			gap_try(x, y, &run, &saw, 0);		}	}	for (n=0; n < ntiles; n++) {		if (tile_has_diff[n]) {			diffs++;		}	}	return diffs;}