subroutine  dscalf(n,da,dx,incx)

c

c     scales a vector by a constant.

c     uses unrolled loops for increment equal to one.

c     jack dongarra, linpack, 3/11/78.

c     modified 3/93 to return if incx .le. 0.

c     modified 12/3/93, array(1) declarations changed to array(*)

c

      double precision da,dx(*)

      integer i,incx,m,mp1,n,nincx

c

      if( n.le.0 .or. incx.le.0 )return

      if(incx.eq.1)go to 20

c

c        code for increment not equal to 1

c

      nincx = n*incx

      do 10 i = 1,nincx,incx

        dx(i) = da*dx(i)

   10 continue

      return

c

c        code for increment equal to 1

c

c

c        clean-up loop

c

   20 m = mod(n,5)

      if( m .eq. 0 ) go to 40

      do 30 i = 1,m

        dx(i) = da*dx(i)

   30 continue

      if( n .lt. 5 ) return

   40 mp1 = m + 1

      do 50 i = mp1,n,5

        dx(i) = da*dx(i)

        dx(i + 1) = da*dx(i + 1)

        dx(i + 2) = da*dx(i + 2)

        dx(i + 3) = da*dx(i + 3)

        dx(i + 4) = da*dx(i + 4)

   50 continue

      return

      end