Do not understand Curve intersections code

I used Curve intersections code and it gives the answer

https://ww2.mathworks.cn/matlabcentral/fileexchange/22441-curve-intersections

But the problem is that I do not understand some part of the code and the algorithm.

For examle what this line do

hF = @le; % line 50

C1 = feval(hF,D(bsxfun(@times,dx1,y2)-bsxfun(@times,dy1,x2),S1),0); % line 63
C2 = feval(hF,D((bsxfun(@times,y1,dx2)-bsxfun(@times,x1,dy2))',S2'),0)'; % line 65

function u = D(x,y)
        u = bsxfun(@minus,x(:,1:end-1),y).*bsxfun(@minus,x(:,2:end),y);
end

what is 'signed distances'

 %...Determine 'signed distances'   
    S1 = dx1.*y1(1:end-1) - dy1.*x1(1:end-1);
    S2 = dx2.*y2(1:end-1) - dy2.*x2(1:end-1);

Answer 1

[darova]

Intersections just loops through all segments of curves and find all intersections

Many of segments have intersections, but intersection point has to be on these segments

Here are equations need to be solved to find intersection point

Try to find x,y and see if this solution has something in common with this

function u = D(x,y)
        u = bsxfun(@minus,x(:,1:end-1),y).*bsxfun(@minus,x(:,2:end),y);
end

[darova]

Look here: Intersections

Piece of explanation from there:

% In principle, we have to perform this computation on every pair of line
% segments in the input data.  This can be quite a large number of pairs so
% we will reduce it by doing a simple preliminary check to eliminate line
% segment pairs that could not possibly cross.  The check is to look at the
% smallest enclosing rectangles (with sides parallel to the axes) for each
% line segment pair and see if they overlap.
% ...

I think the piece of code you posted do the same - checks if enclosing rectangles overlap