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base64decode.m
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base64decode.m
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function res = base64decode(str)
% base64decode Perform Base 64 decoding of a string
% RES = base64decode(V) decodes a string that was encoded using Base 64 encoding as
% documented in RFC 4648, <a href="http://tools.ietf.org/html/rfc4648#section-4">section 4</a> and returns the
% decoded byte array. This encoding is used in a number of contexts in Internet
% messages where arbitrary data must be transmitted in the form of ASCII
% characters.
%
% In the input string, any characters not in the set of 65 characters defined for
% Base 64 encoding are ignored. Decoding stops at the end of string or the first
% occurrence of a '=' character.
%
% If you know that the encoded data was a character string, you can convert it back
% to a string using native2unicode(RES), using the user default encoding in effect
% at the time the string was encoded.
%
% See also base64encode, native2unicode
% Copyright 2016 The MathWorks, Inc.
if isstring(str)
str = char(str);
end
if isempty(str)
res = uint8.empty;
else
validateattributes(str, {'char'}, {'vector'}, mfilename, 'string');
len = length(str);
res(ceil(len*3/4)) = uint8(0);
bx = 1;
i = 1;
j = 0;
out = uint8(0);
while i <= len && j < 4
ch = str(i);
i = i + 1;
if ch >= 'A' && ch <= 'Z'
code = uint8(ch - 'A');
elseif ch >= 'a' && ch <= 'z'
code = uint8(26) + (ch - 'a');
elseif ch >= '0' && ch <= '9'
code = uint8(52) + (ch - '0');
else
switch ch
case '+'
code = uint8(62);
case '/'
code = uint8(63);
case '='
res(bx:end)=[];
break;
otherwise
continue;
end
end
switch j
case 0
out = bitshift(code,2);
j = j + 1;
case 1
res(bx) = out + bitshift(code,-4);
bx = bx + 1;
out = bitshift(code,4);
j = j + 1;
case 2
res(bx) = out + bitshift(code,-2);
bx = bx + 1;
out = bitshift(code,6);
j = j + 1;
case 3
res(bx) = out + code;
bx = bx + 1;
j = 0;
end
end
end
end