share/lapack/blas/fortran/daxpy.f

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