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    1: *> \brief \b DDOT
    2: *
    3: *  =========== DOCUMENTATION ===========
    4: *
    5: * Online html documentation available at
    6: *            http://www.netlib.org/lapack/explore-html/
    7: *
    8: *  Definition:
    9: *  ===========
   10: *
   11: *       DOUBLE PRECISION FUNCTION DDOT(N,DX,INCX,DY,INCY)
   12: *
   13: *       .. Scalar Arguments ..
   14: *       INTEGER INCX,INCY,N
   15: *       ..
   16: *       .. Array Arguments ..
   17: *       DOUBLE PRECISION DX(*),DY(*)
   18: *       ..
   19: *
   20: *
   21: *> \par Purpose:
   22: *  =============
   23: *>
   24: *> \verbatim
   25: *>
   26: *>    DDOT forms the dot product of two vectors.
   27: *>    uses unrolled loops for increments equal to one.
   28: *> \endverbatim
   29: *
   30: *  Arguments:
   31: *  ==========
   32: *
   33: *> \param[in] N
   34: *> \verbatim
   35: *>          N is INTEGER
   36: *>         number of elements in input vector(s)
   37: *> \endverbatim
   38: *>
   39: *> \param[in] DX
   40: *> \verbatim
   41: *>          DX is DOUBLE PRECISION array, dimension ( 1 + ( N - 1 )*abs( INCX ) )
   42: *> \endverbatim
   43: *>
   44: *> \param[in] INCX
   45: *> \verbatim
   46: *>          INCX is INTEGER
   47: *>         storage spacing between elements of DX
   48: *> \endverbatim
   49: *>
   50: *> \param[in] DY
   51: *> \verbatim
   52: *>          DY is DOUBLE PRECISION array, dimension ( 1 + ( N - 1 )*abs( INCY ) )
   53: *> \endverbatim
   54: *>
   55: *> \param[in] INCY
   56: *> \verbatim
   57: *>          INCY is INTEGER
   58: *>         storage spacing between elements of DY
   59: *> \endverbatim
   60: *
   61: *  Authors:
   62: *  ========
   63: *
   64: *> \author Univ. of Tennessee
   65: *> \author Univ. of California Berkeley
   66: *> \author Univ. of Colorado Denver
   67: *> \author NAG Ltd.
   68: *
   69: *> \ingroup double_blas_level1
   70: *
   71: *> \par Further Details:
   72: *  =====================
   73: *>
   74: *> \verbatim
   75: *>
   76: *>     jack dongarra, linpack, 3/11/78.
   77: *>     modified 12/3/93, array(1) declarations changed to array(*)
   78: *> \endverbatim
   79: *>
   80: *  =====================================================================
   81:       DOUBLE PRECISION FUNCTION DDOT(N,DX,INCX,DY,INCY)
   82: *
   83: *  -- Reference BLAS level1 routine --
   84: *  -- Reference BLAS is a software package provided by Univ. of Tennessee,    --
   85: *  -- Univ. of California Berkeley, Univ. of Colorado Denver and NAG Ltd..--
   86: *
   87: *     .. Scalar Arguments ..
   88:       INTEGER INCX,INCY,N
   89: *     ..
   90: *     .. Array Arguments ..
   91:       DOUBLE PRECISION DX(*),DY(*)
   92: *     ..
   93: *
   94: *  =====================================================================
   95: *
   96: *     .. Local Scalars ..
   97:       DOUBLE PRECISION DTEMP
   98:       INTEGER I,IX,IY,M,MP1
   99: *     ..
  100: *     .. Intrinsic Functions ..
  101:       INTRINSIC MOD
  102: *     ..
  103:       DDOT = 0.0d0
  104:       DTEMP = 0.0d0
  105:       IF (N.LE.0) RETURN
  106:       IF (INCX.EQ.1 .AND. INCY.EQ.1) THEN
  107: *
  108: *        code for both increments equal to 1
  109: *
  110: *
  111: *        clean-up loop
  112: *
  113:          M = MOD(N,5)
  114:          IF (M.NE.0) THEN
  115:             DO I = 1,M
  116:                DTEMP = DTEMP + DX(I)*DY(I)
  117:             END DO
  118:             IF (N.LT.5) THEN
  119:                DDOT=DTEMP
  120:             RETURN
  121:             END IF
  122:          END IF
  123:          MP1 = M + 1
  124:          DO I = MP1,N,5
  125:           DTEMP = DTEMP + DX(I)*DY(I) + DX(I+1)*DY(I+1) +
  126:      $            DX(I+2)*DY(I+2) + DX(I+3)*DY(I+3) + DX(I+4)*DY(I+4)
  127:          END DO
  128:       ELSE
  129: *
  130: *        code for unequal increments or equal increments
  131: *          not equal to 1
  132: *
  133:          IX = 1
  134:          IY = 1
  135:          IF (INCX.LT.0) IX = (-N+1)*INCX + 1
  136:          IF (INCY.LT.0) IY = (-N+1)*INCY + 1
  137:          DO I = 1,N
  138:             DTEMP = DTEMP + DX(IX)*DY(IY)
  139:             IX = IX + INCX
  140:             IY = IY + INCY
  141:          END DO
  142:       END IF
  143:       DDOT = DTEMP
  144:       RETURN
  145: *
  146: *     End of DDOT
  147: *
  148:       END