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    1: *> \brief \b DAXPY
    2: *
    3: *  =========== DOCUMENTATION ===========
    4: *
    5: * Online html documentation available at
    6: *            http://www.netlib.org/lapack/explore-html/
    7: *
    8: *  Definition:
    9: *  ===========
   10: *
   11: *       SUBROUTINE DAXPY(N,DA,DX,INCX,DY,INCY)
   12: *
   13: *       .. Scalar Arguments ..
   14: *       DOUBLE PRECISION DA
   15: *       INTEGER INCX,INCY,N
   16: *       ..
   17: *       .. Array Arguments ..
   18: *       DOUBLE PRECISION DX(*),DY(*)
   19: *       ..
   20: *
   21: *
   22: *> \par Purpose:
   23: *  =============
   24: *>
   25: *> \verbatim
   26: *>
   27: *>    DAXPY constant times a vector plus a vector.
   28: *>    uses unrolled loops for increments equal to one.
   29: *> \endverbatim
   30: *
   31: *  Arguments:
   32: *  ==========
   33: *
   34: *> \param[in] N
   35: *> \verbatim
   36: *>          N is INTEGER
   37: *>         number of elements in input vector(s)
   38: *> \endverbatim
   39: *>
   40: *> \param[in] DA
   41: *> \verbatim
   42: *>          DA is DOUBLE PRECISION
   43: *>           On entry, DA specifies the scalar alpha.
   44: *> \endverbatim
   45: *>
   46: *> \param[in] DX
   47: *> \verbatim
   48: *>          DX is DOUBLE PRECISION array, dimension ( 1 + ( N - 1 )*abs( INCX ) )
   49: *> \endverbatim
   50: *>
   51: *> \param[in] INCX
   52: *> \verbatim
   53: *>          INCX is INTEGER
   54: *>         storage spacing between elements of DX
   55: *> \endverbatim
   56: *>
   57: *> \param[in,out] DY
   58: *> \verbatim
   59: *>          DY is DOUBLE PRECISION array, dimension ( 1 + ( N - 1 )*abs( INCY ) )
   60: *> \endverbatim
   61: *>
   62: *> \param[in] INCY
   63: *> \verbatim
   64: *>          INCY is INTEGER
   65: *>         storage spacing between elements of DY
   66: *> \endverbatim
   67: *
   68: *  Authors:
   69: *  ========
   70: *
   71: *> \author Univ. of Tennessee
   72: *> \author Univ. of California Berkeley
   73: *> \author Univ. of Colorado Denver
   74: *> \author NAG Ltd.
   75: *
   76: *> \date November 2017
   77: *
   78: *> \ingroup double_blas_level1
   79: *
   80: *> \par Further Details:
   81: *  =====================
   82: *>
   83: *> \verbatim
   84: *>
   85: *>     jack dongarra, linpack, 3/11/78.
   86: *>     modified 12/3/93, array(1) declarations changed to array(*)
   87: *> \endverbatim
   88: *>
   89: *  =====================================================================
   90:       SUBROUTINE DAXPY(N,DA,DX,INCX,DY,INCY)
   91: *
   92: *  -- Reference BLAS level1 routine (version 3.8.0) --
   93: *  -- Reference BLAS is a software package provided by Univ. of Tennessee,    --
   94: *  -- Univ. of California Berkeley, Univ. of Colorado Denver and NAG Ltd..--
   95: *     November 2017
   96: *
   97: *     .. Scalar Arguments ..
   98:       DOUBLE PRECISION DA
   99:       INTEGER INCX,INCY,N
  100: *     ..
  101: *     .. Array Arguments ..
  102:       DOUBLE PRECISION DX(*),DY(*)
  103: *     ..
  104: *
  105: *  =====================================================================
  106: *
  107: *     .. Local Scalars ..
  108:       INTEGER I,IX,IY,M,MP1
  109: *     ..
  110: *     .. Intrinsic Functions ..
  111:       INTRINSIC MOD
  112: *     ..
  113:       IF (N.LE.0) RETURN
  114:       IF (DA.EQ.0.0d0) RETURN
  115:       IF (INCX.EQ.1 .AND. INCY.EQ.1) THEN
  116: *
  117: *        code for both increments equal to 1
  118: *
  119: *
  120: *        clean-up loop
  121: *
  122:          M = MOD(N,4)
  123:          IF (M.NE.0) THEN
  124:             DO I = 1,M
  125:                DY(I) = DY(I) + DA*DX(I)
  126:             END DO
  127:          END IF
  128:          IF (N.LT.4) RETURN
  129:          MP1 = M + 1
  130:          DO I = MP1,N,4
  131:             DY(I) = DY(I) + DA*DX(I)
  132:             DY(I+1) = DY(I+1) + DA*DX(I+1)
  133:             DY(I+2) = DY(I+2) + DA*DX(I+2)
  134:             DY(I+3) = DY(I+3) + DA*DX(I+3)
  135:          END DO
  136:       ELSE
  137: *
  138: *        code for unequal increments or equal increments
  139: *          not equal to 1
  140: *
  141:          IX = 1
  142:          IY = 1
  143:          IF (INCX.LT.0) IX = (-N+1)*INCX + 1
  144:          IF (INCY.LT.0) IY = (-N+1)*INCY + 1
  145:          DO I = 1,N
  146:           DY(IY) = DY(IY) + DA*DX(IX)
  147:           IX = IX + INCX
  148:           IY = IY + INCY
  149:          END DO
  150:       END IF
  151:       RETURN
  152:       END