sort/shell.adb


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package body Shell is


    -- sequence from Marcin Ciura, 2001
    Gaps : array (Positive range 1 .. 8) of Integer := (701, 301, 132, 57, 23, 10, 4, 1);


    procedure Sort(Arr : in out Array_T) is
        Temp : Element_T;
        Place : Integer;
    begin
        if Arr'Length <= 1 then
            return;
        end if;

        for G of Gaps loop
            for I in Integer range (Index_T'Pos(Arr'First) + G) .. Index_T'Pos(Arr'Last) loop
                Place := I;
                Temp := Arr(Index_T'Val(Place));
                while Place >= (Index_T'Pos(Arr'First) + G) and then Arr(Index_T'Val(Place - G)) > Temp loop
                    Arr(Index_T'Val(Place)) := Arr(Index_T'Val(Place - G));
                    Place := Place - G;
                end loop;
                Arr(Index_T'Val(Place)) := Temp;
            end loop;
        end loop;
    end Sort;


end Shell;