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function outstruct = memmapstream(bytes, format, varargin)
%
% outstruct=memmapstream(bytes, format)
%
% Map a byte-array (in char array or uint8/int8 array) into a structure
% using a dictionary (format is compatible with memmapfile in MATLAB)
%
% This function is compatible with both MATLAB and GNU Octave.
%
% author: Qianqian Fang (q.fang <at> neu.edu)
%
% input:
% bytes: a char, int8 or uint8 vector or array
% format: a 3-column cell array in the format compatible with the
% 'Format' parameter of memmapfile in MATLAB. It has the
% following structure
%
% column 1: data type string, it can be one of the following
% 'int8','int16','int32','int64',
% 'uint8','uint16','uint32','uint64',
% 'single','double','logical'
% column 2: an integer vector denoting the size of the data
% column 3: a string denoting the fieldname in the output struct
%
% For example format={'int8',[1,8],'key'; 'float',[1,1],'value'}
% reads the first 8 bytes from 'bytes' as the first subfield
% 'key' and the following 4 bytes as the floating point 'value'
% subfield.
%
% output:
% outstruct: a structure containing the required field
%
% example:
% bytestream=['Andy' 5 'JT'];
% format={'uint8', [1,4], 'name',
% 'uint8', [1,1], 'age',
% 'uint8', [1,2], 'school'};
% data=memmapstream(bytestream,format);
%
% this file is part of JNIfTI specification: https://github.com/NeuroJSON/jnifti
%
% License: Apache 2.0, see https://github.com/NeuroJSON/jnifti for details
%
if (nargin < 2)
error('must provide bytes and format as inputs');
end
if (~ischar(bytes) && ~isa(bytes, 'int8') && ~isa(bytes, 'uint8') || isempty(bytes))
error('first input, bytes, must be a char-array or uint8/int8 vector');
end
if (~iscell(format) || size(format, 2) < 3 || size(format, 1) == 0 || ~ischar(format{1, 1}))
error('second input, format, must be a 3-column cell array, in a format described by the memmapfile Format field.');
end
bytes = bytes(:)';
datatype = struct('int8', 1, 'int16', 2, 'int32', 4, 'int64', 8, 'uint8', 1, 'uint16', 2, 'uint32', 4, 'uint64', 8, 'single', 4, 'double', 8);
opt = varargin2struct(varargin{:});
opt.usemap = jsonopt('usemap', 0, opt) && exist('containers.Map');
if (opt.usemap)
outstruct = containers.Map();
else
outstruct = struct();
end
len = 1;
for i = 1:size(format, 1)
bytelen = datatype.(format{i, 1}) * prod(format{i, 2});
if (opt.usemap)
outstruct(format{i, 3}) = reshape(typecast(uint8(bytes(len:bytelen + len - 1)), format{i, 1}), format{i, 2});
else
outstruct.(format{i, 3}) = reshape(typecast(uint8(bytes(len:bytelen + len - 1)), format{i, 1}), format{i, 2});
end
len = len + bytelen;
if (len > length(bytes))
break
end
end
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