subroutine bounds(q,N,n1,n2)
*                ======
*     Determine upper and lower bounds
*     --------------------------------
      kk=log2(N)
      n1=0
      n2=N
      m=N
      do 10 k=1,kk+1
      m=m/2
      n1=n1+m
      n2=n2-m
      if(q.le.float(n1)/float(N)) n1=n1-m
      if(q.ge.float(n2)/float(N)) n2=n2+m
10    continue
      return
      end