lzw2norm.m

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function [output,table] = lzw2norm (vector, maxTableSize, restartTable)
%LZW2NORM   LZW Data Compression (decoder)
%   For vectors, LZW2NORM(X) is the uncompressed vector of X using the LZW algorithm.
%   [...,T] = LZW2NORM(X) returns also the table that the algorithm produces.
%
%   For matrices, X(:) is used as input.
%
%   maxTableSize can be used to set a maximum length of the table. Default
%   is 4096 entries, use Inf for unlimited. Usual sizes are 12, 14 and 16
%   bits.
%
%	If restartTable is specified, then the table is flushed when it reaches
%	its maximum size and a new table is built.
%
%   Input must be of uint16 type, while the output is a uint8.
%   Table is a cell array, each element containig the corresponding code.
%
%   
% How it decodes:
%
% Read OLD_CODE
% output OLD_CODE
% CHARACTER = OLD_CODE
% WHILE there are still input characters DO
%     Read NEW_CODE
%     IF NEW_CODE is not in the translation table THEN
%         STRING = get translation of OLD_CODE
%         STRING = STRING+CHARACTER
%     ELSE
%         STRING = get translation of NEW_CODE
%     END of IF
%     output STRING
%     CHARACTER = first character in STRING
%     add translation of OLD_CODE + CHARACTER to the translation table
%     OLD_CODE = NEW_CODE
% END of WHILE


% Ensure to handle uint8 input vector and convert
% to a row
if ~isa(vector,'uint16'),
	error('input argument must be a uint16 vector')
end
vector = vector(:)';

if (nargin < 2)
	maxTableSize = 4096;
	restartTable = 0;
end;
if (nargin < 3)
	restartTable = 0;
end;

	function code = findCode(lastCode, c)
		% Look up code value

		% if (isempty(lastCode))
		% 	fprintf('findCode: ---- + %02x = ', c);
		% else
		% 	fprintf('findCode: %04x + %02x = ', lastCode, c);
		% end;

		if (isempty(lastCode))
			code = c+1;
			%fprintf('%04x\n', code);
			return;
		else
			ii = table.codes(lastCode).prefix;
			jj = find([table.codes(ii).c] == c);
			code = ii(jj);
			% 	if (isempty(code))
			% 		fprintf('----\n');
			% 	else
			% 		fprintf('%04x\n', code);
			% 	end;
			return;
		end;
	end

	function [] = addCode(lastCode, c)
		% Add a new code to the table

		e.c = c;	% NB using variable in parent to avoid allocation cost
		e.lastCode = lastCode;
		e.prefix = [];
		e.codeLength = table.codes(lastCode).codeLength + 1;
		table.codes(table.nextCode) = e;
		table.codes(lastCode).prefix = [table.codes(lastCode).prefix table.nextCode];
		table.nextCode = table.nextCode + 1;

		% if (isempty(lastCode))
		% 	fprintf('addCode   : ---- + %02x = %04x\n', c, table.nextCode-1);
		% else
		% 	fprintf('addCode   : %04x + %02x = %04x\n', lastCode, c, table.nextCode-1);
		% end;
	end

	function str = getCode(code)
		% Output the string for a code

		l = table.codes(code).codeLength;
		str = zeros(1, l);
		for ii = l:-1:1
			str(ii) = table.codes(code).c;
			code = table.codes(code).lastCode;
		end;
	end

	function [] = newTable
		% Build the initial table consisting of all codes of length 1. The strings
		% are stored as prefixCode + character, so that testing is very quick. To
		% speed up searching, we store a list of codes that each code is the prefix
		% for.
		e.c = 0;
		e.lastCode = -1;
		e.prefix = [];
		e.codeLength = 1;
		table.nextCode = 2;
		if (~isinf(maxTableSize))
			table.codes(1:maxTableSize) = e; % Pre-allocate for speed
		else
			table.codes(1:65536) = e; % Pre-allocate for speed
		end;
		for c = 1:255
			e.c = c;
			e.lastCode = -1;
			e.prefix = [];
			e.codeLength = 1;
			table.codes(table.nextCode) = e;
			table.nextCode = table.nextCode + 1;
		end;
	end
%
% Main loop
%
e.c = 0;
e.lastCode = -1;
e.prefix = [];
e.codeLength = 1;
newTable;
output = zeros(1, 3*length(vector), 'uint8'); % assume compression of 33%
outputIndex = 1;
lastCode = vector(1);
output(outputIndex) = table.codes(vector(1)).c;
outputIndex = outputIndex + 1;
character = table.codes(vector(1)).c;
tic;
for vectorIndex=2:length(vector),
	% 	if mod(vectorIndex, 1000) == 0
	% 		fprintf('Index: %5d, Time %.1fs, Table Length %4d, Complete %.1f%%\n', outputIndex, toc, table.nextCode-1, vectorIndex/length(vector)*100); %*ceil(log2(size(table, 2)))/8);
	% 		tic;
	% 	end;

	element = vector(vectorIndex);
	if (element >= table.nextCode)
		% add codes not in table, a special case.
		str = [getCode(lastCode) character];
	else,
		str = getCode(element);
	end
	output(outputIndex + (0:length(str)-1)) = str;
	outputIndex = outputIndex + length(str);
	if ((length(output)-outputIndex) < 1.5*(length(vector)-vectorIndex))
		output = [output zeros(1, 3*(length(vector)-vectorIndex), 'uint8')];
	end;
	if (length(str) < 1)
		keyboard;
	end;
	character = str(1);
	if (table.nextCode <= maxTableSize)
		addCode(lastCode, character);
		if (restartTable && table.nextCode == maxTableSize+1)
			% fprintf('New table\n');
			newTable;
		end;

	end;
	lastCode = element;
end;

output = output(1:outputIndex-1);
table.codes = table.codes(1:table.nextCode-1);

end