NLSL: ddot.f90 Source File

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ddot.f90
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1 double precision function ddot(n,dx,incx,dy,incy)
2 c
3 c forms the dot product of two vectors.
4 c uses unrolled loops for increments equal to one.
5 c jack dongarra, linpack, 3/11/78.
6 c
7 double precision dx(1),dy(1),dtemp
8 integer i,incx,incy,ix,iy,m,mp1,n
9 c
10 ddot = 0.0d0
11 dtemp = 0.0d0
12 if(n.le.0)return
13 if(incx.eq.1.and.incy.eq.1)go to 20
14 c
15 c code for unequal increments or equal increments
16 c not equal to 1
17 c
18 ix = 1
19 iy = 1
20 if(incx.lt.0)ix = (-n+1)*incx + 1
21 if(incy.lt.0)iy = (-n+1)*incy + 1
22 do 10 i = 1,n
23 dtemp = dtemp + dx(ix)*dy(iy)
24 ix = ix + incx
25 iy = iy + incy
26 10 continue
27 ddot = dtemp
28 return
29 c
30 c code for both increments equal to 1
31 c
32 c
33 c clean-up loop
34 c
35 20 m = mod(n,5)
36 if( m .eq. 0 ) go to 40
37 do 30 i = 1,m
38 dtemp = dtemp + dx(i)*dy(i)
39 30 continue
40 if( n .lt. 5 ) go to 60
41 40 mp1 = m + 1
42 do 50 i = mp1,n,5
43 dtemp = dtemp + dx(i)*dy(i) + dx(i + 1)*dy(i + 1) +
44 * dx(i + 2)*dy(i + 2) + dx(i + 3)*dy(i + 3) + dx(i + 4)*dy(i + 4)
45 50 continue
46 60 ddot = dtemp
47 return
48 end
ddot
double precision function ddot(n, dx, incx, dy, incy)
Definition: ddot.f90:2