| 1 |
subroutine saxpy(n,sa,sx,incx,sy,incy) |
| 2 |
c |
| 3 |
c constant times a vector plus a vector. |
| 4 |
c uses unrolled loop for increments equal to one. |
| 5 |
c jack dongarra, linpack, 3/11/78. |
| 6 |
c |
| 7 |
real sx(1),sy(1),sa |
| 8 |
integer i,incx,incy,ix,iy,m,mp1,n |
| 9 |
c |
| 10 |
if(n.le.0)return |
| 11 |
if (sa .eq. 0.0) return |
| 12 |
if(incx.eq.1.and.incy.eq.1)go to 20 |
| 13 |
c |
| 14 |
c code for unequal increments or equal increments |
| 15 |
c not equal to 1 |
| 16 |
c |
| 17 |
ix = 1 |
| 18 |
iy = 1 |
| 19 |
if(incx.lt.0)ix = (-n+1)*incx + 1 |
| 20 |
if(incy.lt.0)iy = (-n+1)*incy + 1 |
| 21 |
do 10 i = 1,n |
| 22 |
sy(iy) = sy(iy) + sa*sx(ix) |
| 23 |
ix = ix + incx |
| 24 |
iy = iy + incy |
| 25 |
10 continue |
| 26 |
return |
| 27 |
c |
| 28 |
c code for both increments equal to 1 |
| 29 |
c |
| 30 |
c |
| 31 |
c clean-up loop |
| 32 |
c |
| 33 |
20 m = mod(n,4) |
| 34 |
if( m .eq. 0 ) go to 40 |
| 35 |
do 30 i = 1,m |
| 36 |
sy(i) = sy(i) + sa*sx(i) |
| 37 |
30 continue |
| 38 |
if( n .lt. 4 ) return |
| 39 |
40 mp1 = m + 1 |
| 40 |
do 50 i = mp1,n,4 |
| 41 |
sy(i) = sy(i) + sa*sx(i) |
| 42 |
sy(i + 1) = sy(i + 1) + sa*sx(i + 1) |
| 43 |
sy(i + 2) = sy(i + 2) + sa*sx(i + 2) |
| 44 |
sy(i + 3) = sy(i + 3) + sa*sx(i + 3) |
| 45 |
50 continue |
| 46 |
return |
| 47 |
end |
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