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    function b = de2bi(varargin)
%DE2BI Convert decimal numbers to binary numbers.
%   B = DE2BI(D) converts a nonnegative integer decimal vector D to a binary
%   matrix B. Each row of the binary matrix B corresponds to one element of D.
%   The default orientation of the of the binary output is Right-MSB; the first
%   element in B represents the lowest bit.
%
%   In addition to the vector input, three optional parameters can be given:
%
%   B = DE2BI(...,N) uses N to define how many digits (columns) are output.
%
%   B = DE2BI(...,N,P) uses P to define which base to convert the decimal
%   elements to.
%
%   B = DE2BI(...,FLAG) uses FLAG to determine the output orientation.  FLAG
%   has two possible values, 'right-msb' and 'left-msb'.  Giving a 'right-msb'
%   FLAG does not change the function's default behavior.  Giving a 'left-msb'
%   FLAG flips the output orientation to display the MSB to the left.
%
%   Examples:
%   ? D = [12; 5];
%
%   ? B = de2bi(D)                  ? B = de2bi(D,5)
%   B =                             B =
%        0     0     1     1             0     0     1     1     0
%        1     0     1     0             1     0     1     0     0
%
%   ? T = de2bi(D,[],3)             ? B = de2bi(D,5,'left-msb')
%   T =                             B =
%        0     1     1                   0     1     1     0     0
%        2     1     0                   0     0     1     0     1
%
%   See also BI2DE.

%   Copyright 1996-2001 The MathWorks, Inc.
%   $Revision: 1.16 $  $Date: 2001/04/23 15:32:11 $

% Typical error checking.
error(nargchk(1,4,nargin));

% --- Placeholder for the signature string.
sigStr = '';
flag = '';
p = [];
n = [];

% --- Identify string and numeric arguments
for i=1:nargin
   if(i>1)
      sigStr(size(sigStr,2)+1) = '/';
   end;
   % --- Assign the string and numeric flags
   if(ischar(varargin{i}))
      sigStr(size(sigStr,2)+1) = 's';
   elseif(isnumeric(varargin{i}))
      sigStr(size(sigStr,2)+1) = 'n';
   else
      error('Only string and numeric arguments are accepted.');
   end;
end;

% --- Identify parameter signitures and assign values to variables
switch sigStr
   % --- de2bi(d)
   case 'n'
      d		= varargin{1};

	% --- de2bi(d, n)
	case 'n/n'
      d		= varargin{1};
      n		= varargin{2};

	% --- de2bi(d, flag)
	case 'n/s'
      d		= varargin{1};
      flag	= varargin{2};

	% --- de2bi(d, n, flag)
	case 'n/n/s'
      d		= varargin{1};
      n		= varargin{2};
      flag	= varargin{3};

	% --- de2bi(d, flag, n)
	case 'n/s/n'
      d		= varargin{1};
      flag	= varargin{2};
      n		= varargin{3};

	% --- de2bi(d, n, p)
	case 'n/n/n'
      d		= varargin{1};
      n		= varargin{2};
      p  	= varargin{3};

	% --- de2bi(d, n, p, flag)
	case 'n/n/n/s'
      d		= varargin{1};
      n		= varargin{2};
      p  	= varargin{3};
      flag	= varargin{4};

	% --- de2bi(d, n, flag, p)
	case 'n/n/s/n'
      d		= varargin{1};
      n		= varargin{2};
      flag	= varargin{3};
      p  	= varargin{4};

	% --- de2bi(d, flag, n, p)
	case 'n/s/n/n'
      d		= varargin{1};
      flag	= varargin{2};
      n		= varargin{3};
      p  	= varargin{4};

   % --- If the parameter list does not match one of these signatures.
   otherwise
      error('Syntax error.');
end;

if isempty(d)
   error('Required parameter empty.');
end

d = d(:);
len_d = length(d);

if max(max(d < 0)) | max(max(~isfinite(d))) | (~isreal(d)) | (max(max(floor(d) ~= d)))
   error('Input must contain only finite real positive integers.');
end

% Assign the base to convert to.
if isempty(p)
    p = 2;
elseif max(size(p) ~= 1)
   error('Destination base must be scalar.');
elseif (~isfinite(p)) | (~isreal(p)) | (floor(p) ~= p)
   error('Destination base must be a finite real integer.');
elseif p < 2
   error('Cannot convert to a base of less than two.');
end;

% Determine minimum length required.
tmp = max(d);
if tmp ~= 0 				% Want base-p log of tmp.
   ntmp = floor( log(tmp) / log(p) ) + 1;
else 							% Since you can't take log(0).
   ntmp = 1;
end

% This takes care of any round off error that occurs for really big inputs.
if ~( (p^ntmp) > tmp )
   ntmp = ntmp + 1;
end

% Assign number of columns in output matrix.
if isempty(n)
   n = ntmp;
elseif max(size(n) ~= 1)
   error('Specified number of columns must be scalar.');
elseif (~isfinite(n)) | (~isreal(n)) | (floor(n) ~= n)
   error('Specified number of columns must be a finite real integer.');
elseif n < ntmp
   error('Specified number of columns in output matrix is too small.');
end

% Check if the string flag is valid.
if isempty(flag)
   flag = 'right-msb';
elseif ~(strcmp(flag, 'right-msb') | strcmp(flag, 'left-msb'))
   error('Invalid string flag.');
end

% Initial value.
b = zeros(len_d, n);

% Perform conversion.
for i = 1 : len_d                   % Cycle through each element of the input vector/matrix.
    j = 1;
    tmp = d(i);
    while (j <= n) & (tmp > 0)      % Cycle through each digit.
        b(i, j) = rem(tmp, p);      % Determine current digit.
        tmp = floor(tmp/p);
        j = j + 1;
    end;
end;

% If a flag is specified to flip the output such that the MSB is to the left.
if strcmp(flag, 'left-msb')

   b2 = b;
   b = b2(:,n:-1:1);

end

% [EOF] de2bi.m