49 lines
1.2 KiB
Fortran
49 lines
1.2 KiB
Fortran
subroutine daxpyf(n,da,dx,incx,dy,incy)
|
|
c
|
|
c constant times a vector plus a vector.
|
|
c uses unrolled loops for increments equal to one.
|
|
c jack dongarra, linpack, 3/11/78.
|
|
c modified 12/3/93, array(1) declarations changed to array(*)
|
|
c
|
|
double precision dx(*),dy(*),da
|
|
integer i,incx,incy,ix,iy,m,mp1,n
|
|
c
|
|
if(n.le.0)return
|
|
if (da .eq. 0.0d0) return
|
|
if(incx.eq.1.and.incy.eq.1)go to 20
|
|
c
|
|
c code for unequal increments or equal increments
|
|
c not equal to 1
|
|
c
|
|
ix = 1
|
|
iy = 1
|
|
if(incx.lt.0)ix = (-n+1)*incx + 1
|
|
if(incy.lt.0)iy = (-n+1)*incy + 1
|
|
do 10 i = 1,n
|
|
dy(iy) = dy(iy) + da*dx(ix)
|
|
ix = ix + incx
|
|
iy = iy + incy
|
|
10 continue
|
|
return
|
|
c
|
|
c code for both increments equal to 1
|
|
c
|
|
c
|
|
c clean-up loop
|
|
c
|
|
20 m = mod(n,4)
|
|
if( m .eq. 0 ) go to 40
|
|
do 30 i = 1,m
|
|
dy(i) = dy(i) + da*dx(i)
|
|
30 continue
|
|
if( n .lt. 4 ) return
|
|
40 mp1 = m + 1
|
|
do 50 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)
|
|
50 continue
|
|
return
|
|
end
|