function coef=comp_dgtreal_ola(f,g,a,M,Lb,phasetype)
%
%  This function implements periodic convolution using overlap-add. The
%  window g is supposed to be extended by fir2iir.
%
%   Url: http://ltfat.github.io/doc/comp/comp_dgtreal_ola.html

% Copyright (C) 2005-2015 Peter L. Soendergaard <peter@sonderport.dk>.
% This file is part of LTFAT version 2.1.1
%
% 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/>.
  
[L W]=size(f);
gl=length(g);
  
N=L/a;
M2=floor(M/2)+1;

% Length of extended block and padded g
Lext=Lb+gl;

% Number of blocks
Nb=L/Lb;

% Number of time positions per block
Nblock   = Lb/a;

if rem(Nblock,1)~=0
  error('The length of the time shift must devide the block length.');
end;

% Number of time positions in half extension
b2 = gl/2/a;

if rem(b2,1)~=0
  error(['The length of the time shift must devide the window length by ' ...
         'an even number.'])
end;

% Extend window to length of extended block.
gpad=fir2long(g,Lext);

coef=zeros(M2,N,W,assert_classname(f,g));

for ii=0:Nb-1
  
  block=comp_sepdgtreal(postpad(f(ii*Lb+1:(ii+1)*Lb,:),Lext),gpad,a,M,phasetype);

  % Large block
  coef(:,ii*Nblock+1:(ii+1)*Nblock,:) = coef(:,ii*Nblock+1:(ii+1)*Nblock,:)+block(:,1:Nblock,:);  
  
  % Small block +
  s_ii=mod(ii+1,Nb);
  coef(:,s_ii*Nblock+1   :s_ii*Nblock+b2,:) = coef(:,s_ii*Nblock+1 ...
                                                   :s_ii*Nblock+b2,:)+ block(:,Nblock+1:Nblock+b2,:); 

  % Small block -
  s_ii=mod(ii-1,Nb)+1;
  coef(:,s_ii*Nblock-b2+1:s_ii*Nblock,:) =coef(:,s_ii*Nblock-b2+1:s_ii*Nblock,:)+ block(:,Nblock+b2+1:Nblock+2*b2,:);

end;


