da_dot.inc

1 real function da_dot(n,x,y)
2 
3    !-----------------------------------------------------------------------
4    ! Purpose: forms the dot product of two vectors.
5    ! uses unrolled loops for increments equal to one.
6    !-----------------------------------------------------------------------
7 
8    implicit none
9 
10    integer, intent(in)               :: n
11    real, dimension(n), intent(in)    :: x,y
12 
13    real dtemp1
14    integer i,m,mp1
15 
16    da_dot = 0.0
17    if (n <= 0)return
18    dtemp1 = 0.0
19 
20    ! code for both increments equal to 1
21 
22    if (n > 0) then
23       m = mod(n,5)
24       if (m /= 0) then
25          do i = 1,m
26             dtemp1 = dtemp1 + x(i)*y(i)
27          end do
28       end if
29       if (n >= 5) then
30          mp1 = m + 1
31          do i = mp1,n,5
32             dtemp1 = dtemp1 + x(i   )*y(i   ) + x(i + 1)*y(i + 1) + &
33                               x(i + 2)*y(i + 2) + x(i + 3)*y(i + 3) + &
34                               x(i + 4)*y(i + 4)
35          end do
36       end if
37    end if
38 
39    da_dot = dtemp1
40 
41 end function da_dot
42 
43