subroutine spread(fc,xwidth,shd)
c
c   0< shd <1.0
c
      implicit none
      include 'itg.par'
c
      real fc(lz),fc2(lz),charac(lz),xwidth,shd,f2max,flimit,y
      integer l
c
      include 'itg.cmn'
c
      if(shd.lt.0.0.or.shd.gt.1.0) then
      shd=0.9
      endif
c
      f2max=0.0
      do 10 l=1,ld
      fc2(l)=fc(l)*fc(l)
      if(fc2(l).ge.f2max) f2max=fc2(l)
   10 continue
c
      flimit=(1.0-shd)*(1.0-shd)*f2max
c
      do 20 l=1,ld
      charac(l)=0.0
      y=fc2(l)
      if(y.gt.flimit) charac(l)=1.0
   20 continue
c
      xwidth=0.5*charac(1)*dr(1)
      do 30 l=2,ldb
      xwidth=xwidth+charac(l)*dr(l)
   30 continue
      xwidth=xwidth+0.5*charac(ld)*dr(ld)
      xwidth=0.5*xwidth
c
      if(xwidth.lt.1.0e-33) then
      xwidth=1.0
      endif
c
      return
      end