50 lines
1.2 KiB
Fortran
50 lines
1.2 KiB
Fortran
real function sdotf(n,sx,incx,sy,incy)
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c
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c forms the dot product of two vectors.
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c uses unrolled loops for increments equal to 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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real sx(*),sy(*),stemp
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integer i,incx,incy,ix,iy,m,mp1,n
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c
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stemp = 0.0e0
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sdotf = 0.0e0
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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
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c not equal 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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stemp = stemp + sx(ix)*sy(iy)
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ix = ix + incx
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iy = iy + incy
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10 continue
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sdotf = stemp
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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,5)
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if( m .eq. 0 ) go to 40
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do 30 i = 1,m
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stemp = stemp + sx(i)*sy(i)
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30 continue
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if( n .lt. 5 ) go to 60
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40 mp1 = m + 1
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do 50 i = mp1,n,5
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stemp = stemp + sx(i)*sy(i) + sx(i + 1)*sy(i + 1) +
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* sx(i + 2)*sy(i + 2) + sx(i + 3)*sy(i + 3) + sx(i + 4)*sy(i + 4)
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50 continue
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60 sdotf = stemp
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return
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end
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