function CF(){
   this.cf=new Array();
   this.cfperiodLWB=-1;this.cfperiodUPB=-1;
   this.cvgt=new Array();  //this.cvgtUPB=-1;  // Array cf may be longer (long period) or shorter than array cvgt
   this.stopped=false; this.cfOFLO=false;
   this.cvgt[-1]=new RAT(1,0,'bot0'); 
};      
CF.prototype.append=   
    function(cfterm){
        if(cfterm<0)HALT("CF terms must be positive");
       if(this.cf.length>100){this.cfOFLO=true;return}
       this.cf[this.cf.length]=cfterm;
       if(this.cvgt.length==0){this.cvgt[0]=new RAT(cfterm,1)}
       else if(!this.stopped)
            {this.cvgt[this.cvgt.length]=new RAT(this.cvgt[this.cvgt.length-1].top*cfterm+this.cvgt[this.cvgt.length-2].top,
                                                 this.cvgt[this.cvgt.length-1].bot*cfterm+this.cvgt[this.cvgt.length-2].bot  );
             DBG(cfterm+":"+this.cvgt[this.cvgt.length-1].top+"/"+this.cvgt[this.cvgt.length-1].bot);
             this.stopped = (    this.cvgt[this.cvgt.length-1].top/this.cvgt[this.cvgt.length-1].bot 
                              == this.cvgt[this.cvgt.length-2].top/this.cvgt[this.cvgt.length-2].bot);
             if(this.stopped){this.cvgt.length=this.cvgt.length-1;}
            };
         //cfSHOW(); confirm("cf.len="+this.cf.length+" cvgt.len="+this.cvgt.length);
       };
CF.prototype.reset=
  function(){ this.cf.length=0; this.cvgt.length=0;this.stopped=false; //this.cvgtUPB=-1; 
              this.cfperiodLWB=-1;  this.cfperiodUPB=-1; this.cfOFLO=false;
            };
CF.prototype.lastcf=
  function(){return this.cf[this.cf.length-1]};
CF.prototype.pop=
  function(){ if(this.stopped || this.cf.length==0)return;
  var x=this.lastcf(); this.cvgt.length=this.cvgt.length-1; this.cf.length=this.cf.length-1;  return x };
CF.prototype.altcf=
 function(){ 
   if(this.stopped || this.cf.length==0 || this.isZero() || this.isPeriodic())return;
   var last=this.pop();  
   if(last==1&&this.cf.length>0)this.append(this.pop()+1)
   else{this.append(last-1);this.append(1)}
 };
CF.prototype.isZero=function(){return this.cf.length==1&&this.cf[0]==0};
CF.prototype.isPeriodic=  function(){return this.cfperiodLWB!=-1};
CF.prototype.cftoString=
 function(){ //alert("PERIODIC? "+this.isPeriodic()+" "+this.cfperiodLWB+".."+this.cfperiodUPB);
   return (this.isPeriodic()  
          ? this.cf.slice(0,this.cfperiodLWB).join(", ")+(this.cfperiodLWB>0?",":"") +" ["+
                 this.cf.slice(this.cfperiodLWB,this.cfperiodUPB+1).join(", ")+"]"  
          : this.cf.slice(0,this.cvgt.length).join(", ")+(this.stopped ? " ..." :"")
          )
 };
CF.prototype.cvgtstoString=
  function(){var s="";
  if(this.isPeriodic())
       {s="This CF "+(this.cfperiodLWB==0?"is ":"ends with ")+" a repeating pattern: \r"
           +this.cftoString().replace(/\[/,(this.cfperiodLWB>0?" then ":" ")).replace(/\]/," repeating for ever")
       };
   if(s!="")s=s+"\r";
   s=s+"Convergents:\r";  
      //Cf.cvgt.slice(0,this.cvgtUPB+1).join(", ")+(this.stopped?" ...":"");
   for(i=0;i<this.cvgt.length;i++)
          s=s+justify(this.cf[i],3,'R')+": "+this.cvgt[i]+" = "+this.cvgt[i].top/this.cvgt[i].bot+"\r";
   if(this.stopped)s=s+"...\r";
   return s
};
CF.prototype.toRAT=
  function(){ //alert("toRAT: "+this.cftoString()+" cvgts end at "+this.cvgt.length-1);
   return this.cvgt[this.cvgt.length-1] };
CF.prototype.toDec=   function(){return eval(this.toRAT().toString())};
CF.prototype.toString=  function(){return this.cftoString()+"\r"+this.cvgtstoString()};
CF.prototype.dump=function(){return "===DUMP cf="+this.toString()+
    "\r "+this.cvgt.length+"=#cvgt "+(this.cvgt.length==1?this.cvgt[0]:"")+" pLWB="+this.cfperiodLWB+
  " pUPB="+this.cfperiodUPB+" stopped="+this.stopped+" OFLO="+this.cfOFLO+" 0?="+this.isZero()+"\r=====\r"};