%!PS

% begin included library code
% see https://codeberg.org/Firedrake/postscript-libraries/
/s2a {
    [ exch { } forall ]
} bind def

/test {
    /test.count test.count 1 add def
    {
        /test.pass test.pass 1 add def
    } {
        ( ) print
        test.count (....) cvs print
        (-fail) print
    } ifelse
} bind def

/apush.right { % [a b] c -> [a b c]
    exch
    [ exch aload length 2 add -1 roll ]
} bind def

/test.start {
    print (:) print
    /test.pass 0 def
    /test.count 0 def
} bind def

/test.end {
    ( ) print
    test.count 0 gt {
        (Passed ) print
        test.pass (...) cvs print
        (/) print
        test.count (...) cvs print
        ( \() print
        test.pass 100 mul test.count idiv (...) cvs print
        (%\)) print
        (\r\n) print
    } if
} bind def

/apop.left { % [a b c] -> [b c] a
    dup 0 get exch
    [ exch aload length -1 roll pop ] exch
} bind def


% end included library code

/cs2xy {
    [ exch
      s2a aload pop
      (1) s2a aload pop sub
      exch
      (a) s2a aload pop sub
      exch
    ]
} bind def

/knightsmove {
    0 dict begin
    cs2xy /tc exch def
    cs2xy /fc exch def
    /queue [ [ fc 0 get fc 1 get 0 ] ] def
    /seen 0 dict def
    -1
    {
        queue length 1 ge {
            queue apop.left /cc exch def /queue exch def
            cc 0 get tc 0 get eq cc 1 get tc 1 get eq and {
                pop cc 2 get
                exit
            } {
                [
                    [2 1]
                    [1 2]
                    [2 -1]
                    [1 -2]
                    [-2 1]
                    [-1 2]
                    [-2 -1]
                    [-1 -2]
                ] {
                    /offset exch def
                    /x cc 0 get offset 0 get add def
                    /y cc 1 get offset 1 get add def
                    x 0 ge x 7 le and y 0 ge and y 7 le and {
                        /cv x 8 mul y add def
                        seen cv known not {
                            /queue queue [ x y cc 2 get 1 add ] apush.right def
                            seen cv true put
                        } if
                    } if
                } forall
            } ifelse
        } {
            exit
        } ifelse
    } loop
    end
} bind def

(knightsmove) test.start
(g2) (a8) knightsmove 4 eq test
(g2) (h2) knightsmove 3 eq test
test.end