Procedure COSFT(var Y:array of real; N, ISIGN:integer);
var
    THETA,WR,WI,WPR,SUM,WTEMP,Y1,Y2,WPI,EVEN,ODD,ENF0,SUM0,SUME:real;
    I,J,M,JJ:integer;
begin
    THETA:=3.14159265358979 / N;
    WR:=1;
    WI:=0;
    WPR:=-2 * Sqr(Sin(0.5 * THETA));
    WPI:=Sin(THETA);
    Sum:=Y[1];
    M:=N div 2;
    For J:=1 To M - 1 do
    begin
        WTEMP:=WR;
        WR:=WR * WPR - WI * WPI + WR;
        WI:=WI * WPR + WTEMP * WPI + WI;
        Y1:=0.5 * (Y[J + 1] + Y[N - J + 1]);
        Y2:=(Y[J + 1] - Y[N - J + 1]);
        Y[J + 1]:=Y1 - WI * Y2;
        Y[N - J + 1]:=Y1 + WI * Y2;
        Sum:=Sum + WR * Y2;
    end; 
    REALFT(Y, M, 1);
    Y[2]:=Sum;
    For JJ:=2 To M  do
    begin
        J:=2*JJ;
        Sum:=Sum + Y[J];
        Y[J]:=Sum;
    end; 
    If ISIGN = -1 Then
    begin
        EVEN:=Y[1];
        ODD:=Y[2];
        For JJ:=1 To M -1 do
        begin
            I:=2*JJ + 1;
            EVEN:=EVEN + Y[I];
            ODD:=ODD + Y[I + 1];
        end;
        ENF0:=2 * (EVEN - ODD);
        SUM0:=Y[1] - ENF0;
        SUME:=(2 * ODD / N) - SUM0;
        Y[1]:=0.5 * ENF0;
        Y[2]:=Y[2] - SUME;
        For JJ:=1 To M -1  do
        begin
            I:=2 * JJ + 1;
            Y[I]:=Y[I] - SUM0;
            Y[I + 1]:=Y[I + 1] - SUME;
        end; 
    end; 
end;