--- /dev/null
+## Copyright (C) 2006 Muthiah Annamalai <muthiah.annamalai@uta.edu>
+##
+## 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/>.
+
+## This function generates the output bits from the PRBS
+## state, for the number of iterations specified.
+##
+## First argument is the PRBS structure obtained from prbs_generator.
+## PRBS iterations is specified in the second argument.
+## PRBS start state is taken from the prbs.sregs.
+##
+## Second argument of the output is PRBS structure with a new
+## state. This allows usage like:
+##
+## [ seq, prbs ] = prbs_iterator( prbs, niterations );
+##
+## while the state of the PRBS is updated.
+##
+## Example: If you had a PRBS shift register like the diagram
+## below with 4 registers we use representation by polynomial
+## of [ 1 2 3 4], and feedback connections between [ 1 3 4 ].
+## The output PRBS sequence is taken from the position 4.
+##
+## +---+ +----+ +---+ +---+
+## | D |----| D |---| D |---| D |
+## +---+ +----+ +---+ +---+
+## | | |
+## \ / /
+## [+]---------------+------+
+## 1 + 0.D + 1.D^2 + 1.D^3
+##
+## The code to implement this PRBS will be
+## prbs=prbs_generator([1 3 4],{[1 3 4]},[1 0 1 1]);
+## x = prbs_iterator(prbs,15)
+##
+## See Also: This function is to be used along with functions
+## prbs_iterator, prbs_generator and prbs_sequence.
+
+function [outputseq, prbs] = prbs_iterator (prbs, iterations = 2^(prbs.reglen)-1)
+
+ if ( nargin < 1 || nargin > 2 )
+ print_usage;
+ endif
+ outputseq=zeros(1,iterations);
+ nstate=zeros(1,prbs.reglen);
+
+ ## For each iteration, shift the output bit. Then compute the xor pattern of connections.
+ ## Finally apply feedback the stuff. Insert the computed pattern.
+ for itr=1:iterations
+ ## save output.
+ outputseq(itr)=prbs.sregs(prbs.reglen);
+
+ ## compute the feedback.
+ for itr2=1:prbs.conlen
+ val=0;
+ L=length(prbs.connections{itr2});
+ for itr3=2:L
+ val=bitxor(val,prbs.sregs(prbs.connections{itr2}(itr3)));
+ endfor
+ nstate(prbs.connections{itr2}(1))=val;
+ endfor
+
+ ## rotate the output discarding the last output.
+ prbs.sregs=[0 prbs.sregs(1:prbs.reglen-1)];
+
+ ## insert the feedback.
+ for itr2=1:prbs.conlen
+ prbs.sregs(itr2)=nstate(itr2);
+ nstate(itr2)=0; # reset.
+ endfor
+
+ endfor
+endfunction
+
+##
+## TEST CASES FOR PRBS.
+##
+##
+## 2^31 -1 : D31 + D28 + 1 =0 inverted
+## 2^23 -1 : D23 + D18 + 1 = 0 ,
+## 2^15 -1 : D15 + D14 + 1 = 0,
+## 2^10 -1 : D10 + D7 + 1 = 0,
+## 2^7 -1 : D7 + D6 + 1 = 0,
+## 2^4 -1 : D3 + D2 + 1 = 0,
+##
+## +---+ +----+ +---+ +---+
+## | D |----| D |---| D |---| D |
+## +---+ +----+ +---+ +---+
+## | | |
+## \ / /
+## [+]---------------+------+
+## 1 + 0.D + 1.D^2 + 1.D^3
+##
+##
+## prbs=prbs_generator([1 3 4],{[1 3 4]},[1 0 1 1]);
+## x = prbs_iterator(prbs,15)
+## y = prbs_iterator(prbs,30)(16:end)
+## z = prbs_sequence(prbs)
+## exit
+## break
+
+##
+## Multiple Tap, Simple Sequence Generator.
+##
+## n=10;
+## k=8;
+## inits=round(abs(rand(1,n)*1.0))
+## prbs=prbs_generator([n 1],{[1 2 k n-1 n]},inits);
+## prbs_iterator(prbs,1023)
+## prbs_seqlength(prbs,inits)
+
+##prbs=prbs_generator([1 2 3],{[1 2 3]},[1 1 1]);
+##prbs_iterator(prbs,7)
+
+##
+## 2^4 -1 : D4 + D1 + 1 = 0,
+##
+## +---+ +----+ +---+ +---+
+## | D |----| D |---| D |---| D |
+## +---+ +----+ +---+ +---+
+## | | |
+## \ / /
+## [+]---------------+------+
+## 1 + 0.D + 1.D^2 + 1.D^3
+##
+##prbs=prbs_generator([1 3 4],{[1 2 4]},[1 0 1 1]);
+##prbs_iterator(prbs,16)
+##prbs_iterator(prbs,32)
+
+
+##prbs=prbs_generator([7],{[1 7 6]},[1 0 0 1 0 0 0]);
+##y=prbs_iterator(prbs,128);
+##x=prbs_iterator(prbs,256);