stdlib_dswap Subroutine

     pure subroutine stdlib_dswap(n,dx,incx,dy,incy)
     !! DSWAP interchanges two vectors.
     !! uses unrolled loops for increments equal to 1.
        ! -- reference blas level1 routine --
        ! -- reference blas is a software package provided by univ. of tennessee,    --
        ! -- univ. of california berkeley, univ. of colorado denver and nag ltd..--
           ! Scalar Arguments 
           integer(ilp), intent(in) :: incx, incy, n
           ! Array Arguments 
           real(dp), intent(inout) :: dx(*), dy(*)
        ! =====================================================================
           ! Local Scalars 
           real(dp) :: dtemp
           integer(ilp) :: i, ix, iy, m, mp1
           ! Intrinsic Functions 
           intrinsic :: mod
           if (n<=0) return
           if (incx==1 .and. incy==1) then
             ! code for both increments equal to 1
             ! clean-up loop
              m = mod(n,3)
              if (m/=0) then
                 do i = 1,m
                    dtemp = dx(i)
                    dx(i) = dy(i)
                    dy(i) = dtemp
                 end do
                 if (n<3) return
              end if
              mp1 = m + 1
              do i = mp1,n,3
                 dtemp = dx(i)
                 dx(i) = dy(i)
                 dy(i) = dtemp
                 dtemp = dx(i+1)
                 dx(i+1) = dy(i+1)
                 dy(i+1) = dtemp
                 dtemp = dx(i+2)
                 dx(i+2) = dy(i+2)
                 dy(i+2) = dtemp
              end do
           else
             ! code for unequal increments or equal increments not equal
               ! to 1
              ix = 1
              iy = 1
              if (incx<0) ix = (-n+1)*incx + 1
              if (incy<0) iy = (-n+1)*incy + 1
              do i = 1,n
                 dtemp = dx(ix)
                 dx(ix) = dy(iy)
                 dy(iy) = dtemp
                 ix = ix + incx
                 iy = iy + incy
              end do
           end if
           return
     end subroutine stdlib_dswap