function ranf(xl,xh,ymax,m,M0)
      
      real*8 ranf,xl,xh,ymax
      real*8 x,y,test,m(3),M0
        real*4 ran_true
       

 100  call ranlux(ran_true,1)
      x=(xh-xl)*dble(ran_true)+xl
     
      call ranlux(ran_true,1)
      y=ymax*dble(ran_true)
      test=dsqrt((x**2-(m(1)+m(2))**2)*(x**2-(m(1)-m(2))**2))/2.d0/x
     >     *dsqrt((M0**2-(x+m(3))**2)*(M0**2-(x-m(3))**2))
     >     /2.d0/M0
     
        
       
      if(test.lt.0.)goto 100
      if(y.gt.test)goto 100
      ranf=x
      return
      end