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## Copyright (C) 2007 Muthiah Annamalai <muthiah.annamalai@uta.edu>
## Copyright (C) 2015 Oliver Heimlich <oheim@posteo.de>
##
## This program is free software; you can redistribute it and/or modify it under
## the terms of the GNU General Public License as published by the Free Software
## Foundation; either version 3 of the License, or (at your option) any later
## version.
##
## This program is distributed in the hope that it will be useful, but WITHOUT
## ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
## FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License for more
## details.
##
## You should have received a copy of the GNU General Public License along with
## this program; if not, see <http://www.gnu.org/licenses/>.
## -*- texinfo -*-
## @deftypefn {Function File} {@var{rval} =} base64decode (@var{code})
## @deftypefnx {Function File} {@var{rval} =} base64decode (@var{code}, @var{as_string})
## Convert a base64 @var{code} (a string of printable characters according to RFC 2045)
## into the original ASCII data set of range 0-255. If option @var{as_string} is
## passed, the return value is converted into a string. Otherwise, the return
## value is a uint8 row vector.
##
## @example
## @group
## base64decode ('SGFrdW5hIE1hdGF0YQ==', true)
## @result{} Hakuna Matata
## @end group
## @end example
##
## See: http://www.ietf.org/rfc/rfc2045.txt
##
## @seealso {base64encode}
## @end deftypefn
function Z = base64decode (X, as_string)
if (nargin < 1 || nargin > 2)
print_usage;
elseif (nargin == 1)
as_string = false;
endif
## strip white space
X((X == ' ') | (X == "\n") | (X == "\r")) = [];
if (any (X(:) < 0) || any(X(:) > 255))
error ("base64decode is expecting integers in the range 0 .. 255");
endif
## convert into ascii code and 8 bit integers to save memory
X = uint8 (X);
## decompose into the 4xN matrices - separation of encoded 3 byte blocks
if (rows (X) ~= 4)
if (rem (numel (X), 4) ~= 0)
error ("base64decode is expecting blocks of 4 characters to decode");
endif
X = reshape (X, [4, numel(X)./4]);
endif
## decode 6-bit values from the incoming matrix &
## write the values into Va matrix.
Va = ones (size(X), 'uint8') .* 65;
iAZ = ((X >= 'A') & (X <= 'Z'));
Va(iAZ) = X(iAZ) - 'A';
iaz = ((X >= 'a') & (X <= 'z'));
Va(iaz) = X(iaz) - 'a' + 26;
i09 = ((X >= '0') & (X <= '9'));
Va(i09) = X(i09) - '0' + 52;
Va(X == '+') = 62;
Va(X == '/') = 63;
padding = (X == '=');
Va(padding) = 0;
if (any (any (Va == 65)))
error ('base64decode is expecting valid characters A..Za..z0..9+/=');
endif
if (not (isempty (X)) && ...
(find (padding, 1) < numel (X) - 1 || ...
(X(end - 1) == '=' && X(end) ~= '=')))
error ('base64decode is expecting max two padding characters at the end');
endif
## decode 4x6 bit into 3x8 bit
B = vertcat (...
Va(1, :) .* 4 + (Va(2, :) - rem (Va(2, :), 16)) ./ 16, ...
rem (Va(2, :), 16) .* 16 + (Va(3, :) - rem (Va(3, :), 4)) ./ 4, ...
rem (Va(3, :), 4) .* 64 + Va(4, :));
## Convert blocks into row vector
Z = B(:).';
## Remove byte blocks which have been introduced by padding
if (not (isempty (X)))
Z(end - sum (padding(end - 1 : end)) + 1 : end) = [];
endif
if (as_string)
Z = char (Z);
end
endfunction
%!assert(base64decode(base64encode('Hakuna Matata'),true),'Hakuna Matata')
%!assert(base64decode(base64encode([1:255])),uint8([1:255]))
%!assert(base64decode(base64encode('taken'),true),'taken')
%!assert(base64decode(base64encode('sax'),true),'sax')
%!assert(base64decode(base64encode('H'),true),'H')
%!assert(base64decode(base64encode('H'),false),uint8('H'))
%!assert(base64decode(base64encode('Ta'),true),'Ta')
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