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subroutine daxpy(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
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