/* Gray code G(n) */
new; cls;
n=5;
print/rz Gray(n);



proc Gray(n);
   retp(eor(n,floor(n/2)));
endp;

proc eor(a,b);
   local a2,b2,dim,y,x;
   a2=dectobin(a);
   b2=dectobin(b);
   dim=maxc(rows(a2)|rows(b2));
   if rows(a2)>rows(b2);
      b2=zeros(rows(a2)-rows(b2),1)|b2;
   elseif rows(a2)<rows(b2);
      a2=zeros(rows(b2)-rows(a2),1)|a2;
   endif;
   y=a2+b2;
   y=y.*(y./=2);
/*
   print a2';
   print b2';
   print;
   print y';
*/
   x=bintodec(y);
   retp(x);
endp;



proc dectobin(x);           /* dec to bin */
   local n,z,y;
   if x==0;
      y=0;
   else;
      n=maxc(log(x)/log(2))+1;
      z=reshape(2,n,rows(x));
      y=rev(recserrc(x,z)); 
   endif;
   retp(y);
endp;

proc bintodec(y);           /* bin to dec */
   if rows(y)==1;
      retp(y);
   else;
      retp(polyeval(2,y));
   endif;
endp;