share/lbfgs/ddot.f

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