#assume we start with the corner points ordered in order of drawing the polygon
@x = (x1, x2, x3, ....);
@y = (y1, y2, y3, ....);

# determine the equations of each side
for $i (0 .. $#@x-1) {
     $m[$i] = ($y[$i+1] - $y[$i])/($x[$i+1] - $x[$i]);
     $b[$i] = $y[$i] - $m[$i]*$x[$i];
}

#test each point
@data_x= (dx1, dx2, dx3, ...);
@data_y= (dy1, dy2, dy3, ...);
for $i (0 .. $#data_y) {
     #find intersection of the line y = $data_y[$i] with each polygon side
     for $j (0 .. $#x-1) {
          if ($m[$j] != 0) {
               $x_intsxn = ($data_y[$i] - $b[$j])/$m[$j];
                    #does that intersection occur within the side's length?
                    if (($x_intsxn > $x[$j] && $x_intsxn < $x[$j+1]) || ($x_intsxn > $x[$j] && $x_intsxn < $x[$j+1])) {
                         #is this intersection to the right or left of the point?
                         if ($x_intsxn > $data_x[$i]) {$right++;}
                         else {$left++;}
                     }
           }
     }
     #test odd/even interesections
     if ($left % 2 && $right % 2) {odd number means point inside polygon, do 'insidepoint' stuff or flag point as inside}
     else {flag point as outside}
}