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diff --git a/gr-trellis/lib/fsm.cc b/gr-trellis/lib/fsm.cc
new file mode 100644
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+++ b/gr-trellis/lib/fsm.cc
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+/* -*- c++ -*- */
+/*
+ * Copyright 2002,2012 Free Software Foundation, Inc.
+ *
+ * This file is part of GNU Radio
+ *
+ * GNU Radio 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, or (at your option)
+ * any later version.
+ *
+ * GNU Radio 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 GNU Radio; see the file COPYING.  If not, write to
+ * the Free Software Foundation, Inc., 51 Franklin Street,
+ * Boston, MA 02110-1301, USA.
+ */
+
+#include <cstdio>
+#include <string>
+#include <iostream>
+#include <fstream>
+#include <stdexcept>
+#include <cmath>
+#include <stdlib.h>
+#include <trellis/base.h>
+#include <trellis/fsm.h>
+
+namespace gr {
+  namespace trellis {
+
+    fsm::fsm()
+    {
+      d_I=0;
+      d_S=0;
+      d_O=0;
+      d_NS.resize(0);
+      d_OS.resize(0);
+      d_PS.resize(0);
+      d_PI.resize(0);
+      d_TMi.resize(0);
+      d_TMl.resize(0);
+    }
+
+    fsm::fsm(const fsm &FSM)
+    {
+      d_I=FSM.I();
+      d_S=FSM.S();
+      d_O=FSM.O();
+      d_NS=FSM.NS();
+      d_OS=FSM.OS();
+      d_PS=FSM.PS(); // is this going to make a deep copy?
+      d_PI=FSM.PI();
+      d_TMi=FSM.TMi();
+      d_TMl=FSM.TMl();
+    }
+
+    fsm::fsm(int I, int S, int O, const std::vector<int> &NS, const std::vector<int> &OS)
+    {
+      d_I=I;
+      d_S=S;
+      d_O=O;
+      d_NS=NS;
+      d_OS=OS;
+
+      generate_PS_PI();
+      generate_TM();
+    }
+
+    //######################################################################
+    //# Read an FSM specification from a file.
+    //# Format (hopefully will become more flexible in the future...):
+    //# I S O (in the first line)
+    //# blank line
+    //# Next state matrix (S lines, each with I integers separated by spaces)
+    //# blank line
+    //# output symbol matrix (S lines, each with I integers separated by spaces)
+    //# optional comments
+    //######################################################################
+    fsm::fsm(const char *name)
+    {
+      FILE *fsmfile;
+
+      if((fsmfile=fopen(name,"r"))==NULL)
+	throw std::runtime_error ("fsm::fsm(const char *name): file open error\n");
+      //printf("file open error in fsm()\n");
+
+      if(fscanf(fsmfile,"%d %d %d\n",&d_I,&d_S,&d_O) == EOF) {
+	if(ferror(fsmfile) != 0)
+	  throw std::runtime_error ("fsm::fsm(const char *name): file read error\n");
+      }
+
+      d_NS.resize(d_I*d_S);
+      d_OS.resize(d_I*d_S);
+
+      for(int i=0;i<d_S;i++) {
+	for(int j=0;j<d_I;j++) {
+	  if(fscanf(fsmfile,"%d",&(d_NS[i*d_I+j])) == EOF) {
+	    if(ferror(fsmfile) != 0)
+	      throw std::runtime_error ("fsm::fsm(const char *name): file read error\n");
+	  }
+	}
+      }
+      for(int i=0;i<d_S;i++) {
+	for(int j=0;j<d_I;j++) {
+	  if(fscanf(fsmfile,"%d",&(d_OS[i*d_I+j])) == EOF) {
+	    if(ferror(fsmfile) != 0)
+	      throw std::runtime_error ("fsm::fsm(const char *name): file read error\n");
+	  }
+	}
+      }
+
+      fclose(fsmfile);
+
+      generate_PS_PI();
+      generate_TM();
+    }
+
+    //######################################################################
+    //# Automatically generate the FSM from the generator matrix
+    //# of a (n,k) binary convolutional code
+    //######################################################################
+    fsm::fsm(int k, int n, const std::vector<int> &G)
+    {
+      // calculate maximum memory requirements for each input stream
+      std::vector<int> max_mem_x(k,-1);
+      int max_mem = -1;
+      for(int i=0;i<k;i++) {
+	for(int j=0;j<n;j++) {
+	  int mem = -1;
+	  if(G[i*n+j]!=0)
+	    mem=(int)(log(double(G[i*n+j]))/log(2.0));
+	  if(mem>max_mem_x[i])
+	    max_mem_x[i]=mem;
+	  if(mem>max_mem)
+	    max_mem=mem;
+	}
+      }
+
+      //printf("max_mem_x\n");
+      //for(int j=0;j<max_mem_x.size();j++) printf("%d ",max_mem_x[j]); printf("\n");
+
+      // calculate total memory requirements to set S
+      int sum_max_mem = 0;
+      for(int i=0;i<k;i++)
+	sum_max_mem += max_mem_x[i];
+
+      //printf("sum_max_mem = %d\n",sum_max_mem);
+
+      d_I=1<<k;
+      d_S=1<<sum_max_mem;
+      d_O=1<<n;
+
+      // binary representation of the G matrix
+      std::vector<std::vector<int> > Gb(k*n);
+      for(int j=0;j<k*n;j++) {
+	Gb[j].resize(max_mem+1);
+	dec2base(G[j],2,Gb[j]);
+	//printf("Gb\n");
+	//for(int m=0;m<Gb[j].size();m++) printf("%d ",Gb[j][m]); printf("\n");
+      }
+
+      // alphabet size of each shift register
+      std::vector<int> bases_x(k);
+      for(int j=0;j<k ;j++)
+	bases_x[j] = 1 << max_mem_x[j];
+      //printf("bases_x\n");
+      //for(int j=0;j<max_mem_x.size();j++) printf("%d ",max_mem_x[j]); printf("\n");
+
+      d_NS.resize(d_I*d_S);
+      d_OS.resize(d_I*d_S);
+
+      std::vector<int> sx(k);
+      std::vector<int> nsx(k);
+      std::vector<int> tx(k);
+      std::vector<std::vector<int> > tb(k);
+      for(int j=0;j<k;j++)
+	tb[j].resize(max_mem+1);
+      std::vector<int> inb(k);
+      std::vector<int> outb(n);
+
+      for(int s=0;s<d_S;s++) {
+	dec2bases(s,bases_x,sx); // split s into k values, each representing one of the k shift registers
+	//printf("state = %d \nstates = ",s);
+	//for(int j=0;j<sx.size();j++) printf("%d ",sx[j]); printf("\n");
+	for(int i=0;i<d_I;i++) {
+	  dec2base(i,2,inb); // input in binary
+	  //printf("input = %d \ninputs = ",i);
+	  //for(int j=0;j<inb.size();j++) printf("%d ",inb[j]); printf("\n");
+
+	  // evaluate next state
+	  for(int j=0;j<k;j++)
+	    nsx[j] = (inb[j]*bases_x[j]+sx[j])/2; // next state (for each shift register) MSB first
+	  d_NS[s*d_I+i]=bases2dec(nsx,bases_x); // collect all values into the new state
+
+	  // evaluate transitions
+	  for(int j=0;j<k;j++)
+	    tx[j] = inb[j]*bases_x[j]+sx[j]; // transition (for each shift register)MSB first
+	  for(int j=0;j<k;j++) {
+	    dec2base(tx[j],2,tb[j]); // transition in binary
+	    //printf("transition = %d \ntransitions = ",tx[j]);
+	    //for(int m=0;m<tb[j].size();m++) printf("%d ",tb[j][m]); printf("\n");
+	  }
+
+	  // evaluate outputs
+	  for(int nn=0;nn<n;nn++) {
+	    outb[nn] = 0;
+	    for(int j=0;j<k;j++) {
+	      for(int m=0;m<max_mem+1;m++)
+		outb[nn] = (outb[nn] + Gb[j*n+nn][m]*tb[j][m]) % 2; // careful: polynomial 1+D ir represented as 110, not as 011
+	      //printf("output %d equals %d\n",nn,outb[nn]);
+	    }
+	  }
+	  d_OS[s*d_I+i] = base2dec(outb,2);
+	}
+      }
+
+      generate_PS_PI();
+      generate_TM();
+    }
+
+    //######################################################################
+    //# Automatically generate an FSM specification describing the
+    //# ISI for a channel
+    //# of length ch_length and a modulation of size mod_size
+    //######################################################################
+    fsm::fsm(int mod_size, int ch_length)
+    {
+      d_I=mod_size;
+      d_S=(int) (pow(1.0*d_I,1.0*ch_length-1)+0.5);
+      d_O=d_S*d_I;
+
+      d_NS.resize(d_I*d_S);
+      d_OS.resize(d_I*d_S);
+
+      for(int s=0;s<d_S;s++) {
+	for(int i=0;i<d_I;i++) {
+	  int t=i*d_S+s;
+	  d_NS[s*d_I+i] = t/d_I;
+	  d_OS[s*d_I+i] = t;
+	}
+      }
+
+      generate_PS_PI();
+      generate_TM();
+    }
+
+    //######################################################################
+    //# Automatically generate an FSM specification describing the
+    //# the trellis for a CPM with h=K/P (relatively prime),
+    //# alphabet size M, and frequency pulse duration L symbols
+    //#
+    //# This FSM is based on the paper by B. Rimoldi
+    //# "A decomposition approach to CPM", IEEE Trans. Info Theory, March 1988
+    //# See also my own notes at http://www.eecs.umich.edu/~anastas/docs/cpm.pdf
+    //######################################################################
+    fsm::fsm(int P, int M, int L)
+    {
+      d_I=M;
+      d_S=(int)(pow(1.0*M,1.0*L-1)+0.5)*P;
+      d_O=(int)(pow(1.0*M,1.0*L)+0.5)*P;
+
+      d_NS.resize(d_I*d_S);
+      d_OS.resize(d_I*d_S);
+      int nv;
+      for(int s=0;s<d_S;s++) {
+	for(int i=0;i<d_I;i++) {
+	  int s1=s/P;
+	  int v=s%P;
+	  int ns1= (i*(int)(pow(1.0*M,1.0*(L-1))+0.5)+s1)/M;
+	  if (L==1)
+	    nv=(i+v)%P;
+	  else
+	    nv=(s1%M+v)%P;
+	  d_NS[s*d_I+i] = ns1*P+nv;
+	  d_OS[s*d_I+i] = i*d_S+s;
+	}
+      }
+
+      generate_PS_PI();
+      generate_TM();
+    }
+
+    //######################################################################
+    //# Automatically generate an FSM specification describing the
+    //# the joint trellis of fsm1 and fsm2
+    //######################################################################
+    fsm::fsm(const fsm &FSM1, const fsm &FSM2)
+    {
+      d_I=FSM1.I()*FSM2.I();
+      d_S=FSM1.S()*FSM2.S();
+      d_O=FSM1.O()*FSM2.O();
+
+      d_NS.resize(d_I*d_S);
+      d_OS.resize(d_I*d_S);
+
+      for(int s=0;s<d_S;s++) {
+	for(int i=0;i<d_I;i++) {
+	  int s1=s/FSM2.S();
+	  int s2=s%FSM2.S();
+	  int i1=i/FSM2.I();
+	  int i2=i%FSM2.I();
+	  d_NS[s*d_I+i] = FSM1.NS()[s1 * FSM1.I() + i1] * FSM2.S() + FSM2.NS()[s2 * FSM2.I() + i2];
+	  d_OS[s*d_I+i] = FSM1.OS()[s1 * FSM1.I() + i1] * FSM2.O() + FSM2.OS()[s2 * FSM2.I() + i2];
+	}
+      }
+
+      generate_PS_PI();
+      generate_TM();
+    }
+
+    //######################################################################
+    //# Generate a new FSM representing n stages through the original FSM
+    //# AKA radix-n FSM
+    //######################################################################
+    fsm::fsm(const fsm &FSM, int n)
+    {
+      d_I=(int) (pow(1.0*FSM.I(),1.0*n)+0.5);
+      d_S=FSM.S();
+      d_O=(int) (pow(1.0*FSM.O(),1.0*n)+0.5);
+
+      d_NS.resize(d_I*d_S);
+      d_OS.resize(d_I*d_S);
+
+      for(int s=0;s<d_S;s++ ) {
+	for(int i=0;i<d_I;i++ ) {
+	  std::vector<int> ii(n);
+	  dec2base(i,FSM.I(),ii);
+	  std::vector<int> oo(n);
+	  int ns=s;
+	  for(int k=0;k<n;k++) {
+	    oo[k]=FSM.OS()[ns*FSM.I()+ii[k]];
+	    ns=FSM.NS()[ns*FSM.I()+ii[k]];
+	  }
+	  d_NS[s*d_I+i]=ns;
+	  d_OS[s*d_I+i]=base2dec(oo,FSM.O());
+	}
+      }
+
+      generate_PS_PI();
+      generate_TM();
+    }
+
+    //######################################################################
+    //# generate the PS and PI tables for later use
+    //######################################################################
+    void
+    fsm::generate_PS_PI()
+    {
+      d_PS.resize(d_S);
+      d_PI.resize(d_S);
+
+      for(int i=0;i<d_S;i++) {
+	d_PS[i].resize(d_I*d_S); // max possible size
+	d_PI[i].resize(d_I*d_S);
+	int j=0;
+	for(int ii=0;ii<d_S;ii++) for(int jj=0;jj<d_I;jj++) {
+	    if(d_NS[ii*d_I+jj]!=i) continue;
+	    d_PS[i][j]=ii;
+	    d_PI[i][j]=jj;
+	    j++;
+	  }
+	d_PS[i].resize(j);
+	d_PI[i].resize(j);
+      }
+    }
+
+    //######################################################################
+    //# generate the termination matrices TMl and TMi for later use
+    //######################################################################
+    void
+    fsm::generate_TM()
+    {
+      d_TMi.resize(d_S*d_S);
+      d_TMl.resize(d_S*d_S);
+
+      for(int i=0;i<d_S*d_S;i++) {
+	d_TMi[i] = -1; // no meaning
+	d_TMl[i] = d_S; //infinity: you need at most S-1 steps
+	if (i/d_S == i%d_S)
+	  d_TMl[i] = 0;
+      }
+
+      for(int s=0;s<d_S;s++) {
+	bool done = false;
+	int attempts = 0;
+	while (done == false && attempts < d_S-1) {
+	  done = find_es(s);
+	  attempts ++;
+	}
+	if (done == false && d_S > 1) {
+	  //throw std::runtime_error ("fsm::generate_TM(): FSM appears to be disconnected\n");
+	  printf("fsm::generate_TM(): FSM appears to be disconnected\n");
+	  printf("state %d cannot be reached from all other states\n",s);
+	}
+      }
+    }
+
+    // find a path from any state to the ending state "es"
+    bool
+    fsm::find_es(int es)
+    {
+      bool done = true;
+      for(int s=0;s<d_S;s++) {
+	if(d_TMl[s*d_S+es] < d_S)
+	  continue;
+	int minl=d_S;
+	int mini=-1;
+	for(int i=0;i<d_I;i++) {
+	  if( 1 + d_TMl[d_NS[s*d_I+i]*d_S+es] < minl) {
+	    minl = 1 + d_TMl[d_NS[s*d_I+i]*d_S+es];
+	    mini = i;
+	  }
+	}
+	if (mini != -1) {
+	  d_TMl[s*d_S+es]=minl;
+	  d_TMi[s*d_S+es]=mini;
+	}
+	else
+	  done = false;
+      }
+      return done;
+    }
+
+    //######################################################################
+    //#  generate trellis representation of FSM as an SVG file
+    //######################################################################
+    void
+    fsm::write_trellis_svg(std::string filename, int number_stages)
+    {
+      std::ofstream trellis_fname (filename.c_str());
+      if(!trellis_fname) {
+	std::cout << "file not found " << std::endl ; exit(-1);
+      }
+      const int TRELLIS_Y_OFFSET = 30;
+      const int TRELLIS_X_OFFSET = 20;
+      const int STAGE_LABEL_Y_OFFSET = 25;
+      const int STAGE_LABEL_X_OFFSET = 20;
+      const int STATE_LABEL_Y_OFFSET = 30;
+      const int STATE_LABEL_X_OFFSET = 5;
+      const int STAGE_STATE_OFFSETS = 10;
+      //   std::cout << "################## BEGIN SVG TRELLIS PIC #####################" << std::endl;
+      trellis_fname << "<svg viewBox = \"0 0 200 200\" version = \"1.1\">" << std::endl;
+
+      for(int stage_num = 0;stage_num < number_stages;stage_num ++) {
+	// draw states
+	for(int state_num = 0;state_num < d_S ; state_num ++ ) {
+	  trellis_fname << "<circle cx = \"" << stage_num * STAGE_STATE_OFFSETS + TRELLIS_X_OFFSET <<
+	    "\" cy = \"" << state_num * STAGE_STATE_OFFSETS + TRELLIS_Y_OFFSET << "\" r = \"1\"/>" << std::endl;
+	  //draw branches
+	  if(stage_num != number_stages-1) {
+	    for(int branch_num = 0;branch_num < d_I; branch_num++) {
+	      trellis_fname << "<line x1 =\"" << STAGE_STATE_OFFSETS * stage_num+ TRELLIS_X_OFFSET  << "\" ";
+	      trellis_fname << "y1 =\"" << state_num * STAGE_STATE_OFFSETS + TRELLIS_Y_OFFSET<< "\" ";
+	      trellis_fname << "x2 =\"" <<  STAGE_STATE_OFFSETS *stage_num + STAGE_STATE_OFFSETS+ TRELLIS_X_OFFSET << "\" ";
+	      trellis_fname << "y2 =\"" << d_NS[d_I * state_num + branch_num] * STAGE_STATE_OFFSETS + TRELLIS_Y_OFFSET << "\" ";
+	      trellis_fname << " stroke-dasharray = \"3," <<  branch_num << "\" ";
+	      trellis_fname << " stroke = \"black\" stroke-width = \"0.3\"/>" << std::endl;
+	    }
+	  }
+	}
+      }
+      // label the stages
+      trellis_fname << "<g font-size = \"4\" font= \"times\" fill = \"black\">" << std::endl;
+      for(int stage_num = 0;stage_num < number_stages ;stage_num ++) {
+	trellis_fname << "<text x = \"" << stage_num * STAGE_STATE_OFFSETS + STAGE_LABEL_X_OFFSET <<
+	  "\" y = \""  << STAGE_LABEL_Y_OFFSET  << "\" >" << std::endl;
+	trellis_fname << stage_num <<  std::endl;
+	trellis_fname << "</text>" << std::endl;
+      }
+      trellis_fname << "</g>" << std::endl;
+
+      // label the states
+      trellis_fname << "<g font-size = \"4\" font= \"times\" fill = \"black\">" << std::endl;
+      for(int state_num = 0;state_num < d_S ; state_num ++) {
+	trellis_fname << "<text y = \"" << state_num * STAGE_STATE_OFFSETS + STATE_LABEL_Y_OFFSET <<
+	  "\" x = \""  << STATE_LABEL_X_OFFSET  << "\" >" << std::endl;
+	trellis_fname << state_num <<  std::endl;
+	trellis_fname << "</text>" << std::endl;
+      }
+      trellis_fname << "</g>" << std::endl;
+
+      trellis_fname << "</svg>" << std::endl;
+      //  std::cout << "################## END SVG TRELLIS PIC ##################### " << std::endl;
+      trellis_fname.close();
+    }
+
+    //######################################################################
+    //# Write trellis specification to a text file,
+    //# in the same format used when reading FSM files
+    //######################################################################
+    void
+    fsm::write_fsm_txt(std::string filename)
+    {
+      std::ofstream trellis_fname (filename.c_str());
+      if(!trellis_fname) {
+	std::cout << "file not found " << std::endl ; exit(-1);
+      }
+      trellis_fname << d_I << ' ' << d_S << ' ' << d_O << std::endl;
+      trellis_fname << std::endl;
+      for(int i=0;i<d_S;i++) {
+	for(int j=0;j<d_I;j++)
+	  trellis_fname << d_NS[i*d_I+j] << ' ';
+	trellis_fname << std::endl;
+      }
+      trellis_fname << std::endl;
+      for(int i=0;i<d_S;i++) {
+	for(int j=0;j<d_I;j++)
+	  trellis_fname << d_OS[i*d_I+j] << ' ';
+	trellis_fname << std::endl;
+      }
+      trellis_fname << std::endl;
+      trellis_fname.close();
+    }
+
+  } /* namespace trellis */
+} /* namespace gr */