56 lines
1.3 KiB
Fortran
56 lines
1.3 KiB
Fortran
subroutine dswapf (n,dx,incx,dy,incy)
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c
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c interchanges two vectors.
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c uses unrolled loops for increments equal one.
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c jack dongarra, linpack, 3/11/78.
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c modified 12/3/93, array(1) declarations changed to array(*)
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c
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double precision dx(*),dy(*),dtemp
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integer i,incx,incy,ix,iy,m,mp1,n
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c
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if(n.le.0)return
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if(incx.eq.1.and.incy.eq.1)go to 20
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c
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c code for unequal increments or equal increments not equal
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c to 1
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c
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ix = 1
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iy = 1
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if(incx.lt.0)ix = (-n+1)*incx + 1
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if(incy.lt.0)iy = (-n+1)*incy + 1
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do 10 i = 1,n
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dtemp = dx(ix)
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dx(ix) = dy(iy)
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dy(iy) = dtemp
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ix = ix + incx
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iy = iy + incy
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10 continue
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return
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c
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c code for both increments equal to 1
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c
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c
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c clean-up loop
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c
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20 m = mod(n,3)
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if( m .eq. 0 ) go to 40
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do 30 i = 1,m
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dtemp = dx(i)
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dx(i) = dy(i)
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dy(i) = dtemp
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30 continue
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if( n .lt. 3 ) return
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40 mp1 = m + 1
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do 50 i = mp1,n,3
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dtemp = dx(i)
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dx(i) = dy(i)
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dy(i) = dtemp
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dtemp = dx(i + 1)
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dx(i + 1) = dy(i + 1)
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dy(i + 1) = dtemp
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dtemp = dx(i + 2)
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dx(i + 2) = dy(i + 2)
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dy(i + 2) = dtemp
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50 continue
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return
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end
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