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    1: *> \brief \b DSWAP
    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 DSWAP(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: *>    DSWAP interchanges two vectors.
   27: *>    uses unrolled loops for increments equal to 1.
   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,out] 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,out] 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: *> \date November 2017
   70: *
   71: *> \ingroup double_blas_level1
   72: *
   73: *> \par Further Details:
   74: *  =====================
   75: *>
   76: *> \verbatim
   77: *>
   78: *>     jack dongarra, linpack, 3/11/78.
   79: *>     modified 12/3/93, array(1) declarations changed to array(*)
   80: *> \endverbatim
   81: *>
   82: *  =====================================================================
   83:       SUBROUTINE DSWAP(N,DX,INCX,DY,INCY)
   84: *
   85: *  -- Reference BLAS level1 routine (version 3.8.0) --
   86: *  -- Reference BLAS is a software package provided by Univ. of Tennessee,    --
   87: *  -- Univ. of California Berkeley, Univ. of Colorado Denver and NAG Ltd..--
   88: *     November 2017
   89: *
   90: *     .. Scalar Arguments ..
   91:       INTEGER INCX,INCY,N
   92: *     ..
   93: *     .. Array Arguments ..
   94:       DOUBLE PRECISION DX(*),DY(*)
   95: *     ..
   96: *
   97: *  =====================================================================
   98: *
   99: *     .. Local Scalars ..
  100:       DOUBLE PRECISION DTEMP
  101:       INTEGER I,IX,IY,M,MP1
  102: *     ..
  103: *     .. Intrinsic Functions ..
  104:       INTRINSIC MOD
  105: *     ..
  106:       IF (N.LE.0) RETURN
  107:       IF (INCX.EQ.1 .AND. INCY.EQ.1) THEN
  108: *
  109: *       code for both increments equal to 1
  110: *
  111: *
  112: *       clean-up loop
  113: *
  114:          M = MOD(N,3)
  115:          IF (M.NE.0) THEN
  116:             DO I = 1,M
  117:                DTEMP = DX(I)
  118:                DX(I) = DY(I)
  119:                DY(I) = DTEMP
  120:             END DO
  121:             IF (N.LT.3) RETURN
  122:          END IF
  123:          MP1 = M + 1
  124:          DO I = MP1,N,3
  125:             DTEMP = DX(I)
  126:             DX(I) = DY(I)
  127:             DY(I) = DTEMP
  128:             DTEMP = DX(I+1)
  129:             DX(I+1) = DY(I+1)
  130:             DY(I+1) = DTEMP
  131:             DTEMP = DX(I+2)
  132:             DX(I+2) = DY(I+2)
  133:             DY(I+2) = DTEMP
  134:          END DO
  135:       ELSE
  136: *
  137: *       code for unequal increments or equal increments not equal
  138: *         to 1
  139: *
  140:          IX = 1
  141:          IY = 1
  142:          IF (INCX.LT.0) IX = (-N+1)*INCX + 1
  143:          IF (INCY.LT.0) IY = (-N+1)*INCY + 1
  144:          DO I = 1,N
  145:             DTEMP = DX(IX)
  146:             DX(IX) = DY(IY)
  147:             DY(IY) = DTEMP
  148:             IX = IX + INCX
  149:             IY = IY + INCY
  150:          END DO
  151:       END IF
  152:       RETURN
  153:       END