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2608
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1 double precision function ddot(n,dx,incx,dy,incy) |
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2 c |
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3 c forms the dot product of two vectors. |
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4 c uses unrolled loops for increments equal to one. |
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5 c jack dongarra, linpack, 3/11/78. |
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6 c modified 12/3/93, array(1) declarations changed to array(*) |
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7 c |
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8 double precision dx(*),dy(*),dtemp |
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9 integer i,incx,incy,ix,iy,m,mp1,n |
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10 c |
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11 ddot = 0.0d0 |
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12 dtemp = 0.0d0 |
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13 if(n.le.0)return |
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14 if(incx.eq.1.and.incy.eq.1)go to 20 |
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15 c |
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16 c code for unequal increments or equal increments |
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17 c not equal to 1 |
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18 c |
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19 ix = 1 |
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20 iy = 1 |
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21 if(incx.lt.0)ix = (-n+1)*incx + 1 |
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22 if(incy.lt.0)iy = (-n+1)*incy + 1 |
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23 do 10 i = 1,n |
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24 dtemp = dtemp + dx(ix)*dy(iy) |
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25 ix = ix + incx |
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26 iy = iy + incy |
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27 10 continue |
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28 ddot = dtemp |
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29 return |
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30 c |
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31 c code for both increments equal to 1 |
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32 c |
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33 c |
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34 c clean-up loop |
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35 c |
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36 20 m = mod(n,5) |
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37 if( m .eq. 0 ) go to 40 |
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38 do 30 i = 1,m |
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39 dtemp = dtemp + dx(i)*dy(i) |
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40 30 continue |
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41 if( n .lt. 5 ) go to 60 |
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42 40 mp1 = m + 1 |
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43 do 50 i = mp1,n,5 |
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44 dtemp = dtemp + dx(i)*dy(i) + dx(i + 1)*dy(i + 1) + |
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45 * dx(i + 2)*dy(i + 2) + dx(i + 3)*dy(i + 3) + dx(i + 4)*dy(i + 4) |
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46 50 continue |
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47 60 ddot = dtemp |
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48 return |
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49 end |
