share/lbfgs/daxpy.f

   1 C
   2 C
   3 C   ----------------------------------------------------------
   4 C
   5       subroutine daxpy(n,da,dx,incx,dy,incy)
   6 c
   7 c     constant times a vector plus a vector.
   8 c     uses unrolled loops for increments equal to one.
   9 c     jack dongarra, linpack, 3/11/78.
  10 c
  11       double precision dx(1),dy(1),da
  12       integer i,incx,incy,ix,iy,m,mp1,n
  13 c
  14       if(n.le.0)return
  15       if (da .eq. 0.0d0) return
  16       if(incx.eq.1.and.incy.eq.1)go to 20
  17 c
  18 c        code for unequal increments or equal increments
  19 c          not equal to 1
  20 c
  21       ix = 1
  22       iy = 1
  23       if(incx.lt.0)ix = (-n+1)*incx + 1
  24       if(incy.lt.0)iy = (-n+1)*incy + 1
  25       do 10 i = 1,n
  26         dy(iy) = dy(iy) + da*dx(ix)
  27         ix = ix + incx
  28         iy = iy + incy
  29    10 continue
  30       return
  31 c
  32 c        code for both increments equal to 1
  33 c
  34 c
  35 c        clean-up loop
  36 c
  37    20 m = mod(n,4)
  38       if( m .eq. 0 ) go to 40
  39       do 30 i = 1,m
  40         dy(i) = dy(i) + da*dx(i)
  41    30 continue
  42       if( n .lt. 4 ) return
  43    40 mp1 = m + 1
  44       do 50 i = mp1,n,4
  45         dy(i) = dy(i) + da*dx(i)
  46         dy(i + 1) = dy(i + 1) + da*dx(i + 1)
  47         dy(i + 2) = dy(i + 2) + da*dx(i + 2)
  48         dy(i + 3) = dy(i + 3) + da*dx(i + 3)
  49    50 continue
  50       return
  51       end