function y = base64encode(x, eol)

%BASE64ENCODE Perform base64 encoding on a string.

%

%   BASE64ENCODE(STR, EOL) encode the given string STR.  EOL is the line ending

%   sequence to use; it is optional and defaults to '\n' (ASCII decimal 10).

%   The returned encoded string is broken into lines of no more than 76

%   characters each, and each line will end with EOL unless it is empty.  Let

%   EOL be empty if you do not want the encoded string broken into lines.

%

%   STR and EOL don't have to be strings (i.e., char arrays).  The only

%   requirement is that they are vectors containing values in the range 0-255.

%

%   This function may be used to encode strings into the Base64 encoding

%   specified in RFC 2045 - MIME (Multipurpose Internet Mail Extensions).  The

%   Base64 encoding is designed to represent arbitrary sequences of octets in a

%   form that need not be humanly readable.  A 65-character subset

%   ([A-Za-z0-9+/=]) of US-ASCII is used, enabling 6 bits to be represented per

%   printable character.

%

%   Examples

%   --------

%

%   If you want to encode a large file, you should encode it in chunks that are

%   a multiple of 57 bytes.  This ensures that the base64 lines line up and

%   that you do not end up with padding in the middle.  57 bytes of data fills

%   one complete base64 line (76 == 57*4/3):

%

%   If ifid and ofid are two file identifiers opened for reading and writing,

%   respectively, then you can base64 encode the data with

%

%      while ~feof(ifid)

%         fwrite(ofid, base64encode(fread(ifid, 60*57)));

%      end

%

%   or, if you have enough memory,

%

%      fwrite(ofid, base64encode(fread(ifid)));

%

%   See also BASE64DECODE.



%   Author:      Peter J. Acklam

%   Time-stamp:  2004-02-03 21:36:56 +0100

%   E-mail:      pjacklam@online.no

%   URL:         http://home.online.no/~pjacklam



   % check number of input arguments

   error(nargchk(1, 2, nargin));



   % make sure we have the EOL value

   if nargin < 2

      eol = ''; %sprintf('\n');

   else

      if sum(size(eol) > 1) > 1

         error('EOL must be a vector.');

      end

      if any(eol(:) > 255)

         error('EOL can not contain values larger than 255.');

      end

   end



   if sum(size(x) > 1) > 1

      error('STR must be a vector.');

   end



   x   = uint8(x);

   eol = uint8(eol);



   ndbytes = length(x);                 % number of decoded bytes

   nchunks = ceil(ndbytes / 3);         % number of chunks/groups

   nebytes = 4 * nchunks;               % number of encoded bytes



   % add padding if necessary, to make the length of x a multiple of 3

   if rem(ndbytes, 3)

      x(end+1 : 3*nchunks) = 0;

   end



   x = reshape(x, [3, nchunks]);        % reshape the data

   y = repmat(uint8(0), 4, nchunks);    % for the encoded data



   %%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%

   % Split up every 3 bytes into 4 pieces

   %

   %    aaaaaabb bbbbcccc ccdddddd

   %

   % to form

   %

   %    00aaaaaa 00bbbbbb 00cccccc 00dddddd

   %

   y(1,:) = bitshift(x(1,:), -2);                  % 6 highest bits of x(1,:)



   y(2,:) = bitshift(bitand(x(1,:), 3), 4);        % 2 lowest bits of x(1,:)

   y(2,:) = bitor(y(2,:), bitshift(x(2,:), -4));   % 4 highest bits of x(2,:)



   y(3,:) = bitshift(bitand(x(2,:), 15), 2);       % 4 lowest bits of x(2,:)

   y(3,:) = bitor(y(3,:), bitshift(x(3,:), -6));   % 2 highest bits of x(3,:)



   y(4,:) = bitand(x(3,:), 63);                    % 6 lowest bits of x(3,:)



   %%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%

   % Now perform the following mapping

   %

   %   0  - 25  ->  A-Z

   %   26 - 51  ->  a-z

   %   52 - 61  ->  0-9

   %   62       ->  +

   %   63       ->  /

   %

   % We could use a mapping vector like

   %

   %   ['A':'Z', 'a':'z', '0':'9', '+/']

   %

   % but that would require an index vector of class double.

   %

   z = repmat(uint8(0), size(y));

   i =           y <= 25;  z(i) = 'A'      + double(y(i));

   i = 26 <= y & y <= 51;  z(i) = 'a' - 26 + double(y(i));

   i = 52 <= y & y <= 61;  z(i) = '0' - 52 + double(y(i));

   i =           y == 62;  z(i) = '+';

   i =           y == 63;  z(i) = '/';

   y = z;



   %%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%

   % Add padding if necessary.

   %

   npbytes = 3 * nchunks - ndbytes;     % number of padding bytes

   if npbytes

      y(end-npbytes+1 : end) = '=';     % '=' is used for padding

   end



   if isempty(eol)



      % reshape to a row vector

      y = reshape(y, [1, nebytes]);



   else



      nlines = ceil(nebytes / 76);      % number of lines

      neolbytes = length(eol);          % number of bytes in eol string



      % pad data so it becomes a multiple of 76 elements

      y(nebytes + 1 : 76 * nlines) = 0;

      y = reshape(y, 76, nlines);



      % insert eol strings

      eol = eol(:);

      y(end + 1 : end + neolbytes, :) = eol(:, ones(1, nlines));



      % remove padding, but keep the last eol string

      m = nebytes + neolbytes * (nlines - 1);

      n = (76+neolbytes)*nlines - neolbytes;

      y(m+1 : n) = '';



      % extract and reshape to row vector

      y = reshape(y, 1, m+neolbytes);



   end



   % output is a character array

   y = char(y);