stdlib_daxpy Subroutine

     pure subroutine stdlib_daxpy(n,da,dx,incx,dy,incy)
     !! DAXPY constant times a vector plus a vector.
     !! uses unrolled loops for increments equal to one.
        ! -- 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 
           real(dp), intent(in) :: da
           integer(ilp), intent(in) :: incx, incy, n
           ! Array Arguments 
           real(dp), intent(in) :: dx(*)
           real(dp), intent(inout) :: dy(*)
        ! =====================================================================
           ! Local Scalars 
           integer(ilp) :: i, ix, iy, m, mp1
           ! Intrinsic Functions 
           intrinsic :: mod
           if (n<=0) return
           if (da==0.0_dp) return
           if (incx==1 .and. incy==1) then
              ! code for both increments equal to 1
              ! clean-up loop
              m = mod(n,4)
              if (m/=0) then
                 do i = 1,m
                    dy(i) = dy(i) + da*dx(i)
                 end do
              end if
              if (n<4) return
              mp1 = m + 1
              do i = mp1,n,4
                 dy(i) = dy(i) + da*dx(i)
                 dy(i+1) = dy(i+1) + da*dx(i+1)
                 dy(i+2) = dy(i+2) + da*dx(i+2)
                 dy(i+3) = dy(i+3) + da*dx(i+3)
              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
               dy(iy) = dy(iy) + da*dx(ix)
               ix = ix + incx
               iy = iy + incy
              end do
           end if
           return
     end subroutine stdlib_daxpy