|
- subroutine dswapf (n,dx,incx,dy,incy)
- c
- c interchanges two vectors.
- c uses unrolled loops for increments equal one.
- c jack dongarra, linpack, 3/11/78.
- c modified 12/3/93, array(1) declarations changed to array(*)
- c
- double precision dx(*),dy(*),dtemp
- integer i,incx,incy,ix,iy,m,mp1,n
- c
- if(n.le.0)return
- if(incx.eq.1.and.incy.eq.1)go to 20
- c
- c code for unequal increments or equal increments not equal
- c 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
- dtemp = dx(ix)
- dx(ix) = dy(iy)
- dy(iy) = dtemp
- 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,3)
- if( m .eq. 0 ) go to 40
- do 30 i = 1,m
- dtemp = dx(i)
- dx(i) = dy(i)
- dy(i) = dtemp
- 30 continue
- if( n .lt. 3 ) return
- 40 mp1 = m + 1
- do 50 i = mp1,n,3
- dtemp = dx(i)
- dx(i) = dy(i)
- dy(i) = dtemp
- dtemp = dx(i + 1)
- dx(i + 1) = dy(i + 1)
- dy(i + 1) = dtemp
- dtemp = dx(i + 2)
- dx(i + 2) = dy(i + 2)
- dy(i + 2) = dtemp
- 50 continue
- return
- end
|
