邮件解码之二

(* //
  标题:邮件解码之二
  说明:Base64
  设计:Zswang
  日期:2002-02-21
  支持:wjhu111@21cn.com
  // *)
/// ////Begin Source
const
    cBase64 = 'ABCDEFGHIJKLMNOPQRSTUVWXYZabcdefghijklmnopqrstuvwxyz0123456789+/=';

function Base64Encode(mSource: string; mAddLine: Boolean = True): string;
var
    I, J: Integer;
    S: string;
begin
    Result := '';
    J := 0;
    for I := 0 to Length(mSource) div 3 - 1 do
    begin
        S := Copy(mSource, I * 3 + 1, 3);
        Result := Result + cBase64[Ord(S[1]) shr 2 + 1];
        Result := Result + cBase64[((Ord(S[1]) and $03) shl 4) + (Ord(S[2]) shr 4) + 1];
        Result := Result + cBase64[((Ord(S[2]) and $0F) shl 2) + (Ord(S[3]) shr 6) + 1];
        Result := Result + cBase64[Ord(S[3]) and $3F + 1];
        if mAddLine then
        begin
            Inc(J, 4);
            if J >= 76 then
            begin
                Result := Result + #13#10;
                J := 0;
            end;
        end;
    end;
    I := Length(mSource) div 3;
    S := Copy(mSource, I * 3 + 1, 3);
    case Length(S) of
        1:
            begin
                Result := Result + cBase64[Ord(S[1]) shr 2 + 1];
                Result := Result + cBase64[(Ord(S[1]) and $03) shl 4 + 1];
                Result := Result + cBase64[65];
                Result := Result + cBase64[65];
            end;
        2:
            begin
                Result := Result + cBase64[Ord(S[1]) shr 2 + 1];
                Result := Result + cBase64[((Ord(S[1]) and $03) shl 4) + (Ord(S[2]) shr 4) + 1];
                Result := Result + cBase64[(Ord(S[2]) and $0F) shl 2 + 1];
                Result := Result + cBase64[65];
            end;
    end;
end; { Base64Encode }

function Base64Decode(mCode: string): string;
var
    I, L: Integer;
    S: string;
begin
    Result := '';
    L := Length(mCode);
    I := 1;
    while I <= L do
    begin
        if Pos(mCode[I], cBase64) > 0 then
        begin
            S := Copy(mCode, I, 4);
            if (Length(S) = 4) then
            begin
                Result := Result + Chr((Pos(S[1], cBase64) - 1) shl 2 + (Pos(S[2], cBase64) - 1) shr 4);
                if S[3] <> cBase64[65] then
                begin
                    Result := Result + Chr(((Pos(S[2], cBase64) - 1) and $0F) shl 4 + (Pos(S[3], cBase64) - 1) shr 2);
                    if S[4] <> cBase64[65] then
                        Result := Result + Chr(((Pos(S[3], cBase64) - 1) and $03) shl 6 + (Pos(S[4], cBase64) - 1));
                end;
            end;
            Inc(I, 4);
        end
        else
            Inc(I);
    end;
end; { Base64Decode }

/// ////End Source
/// ////Begin Demo
procedure TForm1.Button1Click(Sender: TObject);
begin
    Memo2.Text := Base64Encode(Memo1.Text);
end;

procedure TForm1.Button2Click(Sender: TObject);
begin
    Memo1.Text := Base64Decode(Memo2.Text);
end;
/// ////End Demo