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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: *>    interchanges two vectors.
   27: *>    uses unrolled loops for increments equal one.
   28: *> \endverbatim
   29: *
   30: *  Authors:
   31: *  ========
   32: *
   33: *> \author Univ. of Tennessee
   34: *> \author Univ. of California Berkeley
   35: *> \author Univ. of Colorado Denver
   36: *> \author NAG Ltd.
   37: *
   38: *> \date December 2016
   39: *
   40: *> \ingroup double_blas_level1
   41: *
   42: *> \par Further Details:
   43: *  =====================
   44: *>
   45: *> \verbatim
   46: *>
   47: *>     jack dongarra, linpack, 3/11/78.
   48: *>     modified 12/3/93, array(1) declarations changed to array(*)
   49: *> \endverbatim
   50: *>
   51: *  =====================================================================
   52:       SUBROUTINE DSWAP(N,DX,INCX,DY,INCY)
   53: *
   54: *  -- Reference BLAS level1 routine (version 3.7.0) --
   55: *  -- Reference BLAS is a software package provided by Univ. of Tennessee,    --
   56: *  -- Univ. of California Berkeley, Univ. of Colorado Denver and NAG Ltd..--
   57: *     December 2016
   58: *
   59: *     .. Scalar Arguments ..
   60:       INTEGER INCX,INCY,N
   61: *     ..
   62: *     .. Array Arguments ..
   63:       DOUBLE PRECISION DX(*),DY(*)
   64: *     ..
   65: *
   66: *  =====================================================================
   67: *
   68: *     .. Local Scalars ..
   69:       DOUBLE PRECISION DTEMP
   70:       INTEGER I,IX,IY,M,MP1
   71: *     ..
   72: *     .. Intrinsic Functions ..
   73:       INTRINSIC MOD
   74: *     ..
   75:       IF (N.LE.0) RETURN
   76:       IF (INCX.EQ.1 .AND. INCY.EQ.1) THEN
   77: *
   78: *       code for both increments equal to 1
   79: *
   80: *
   81: *       clean-up loop
   82: *
   83:          M = MOD(N,3)
   84:          IF (M.NE.0) THEN
   85:             DO I = 1,M
   86:                DTEMP = DX(I)
   87:                DX(I) = DY(I)
   88:                DY(I) = DTEMP
   89:             END DO
   90:             IF (N.LT.3) RETURN
   91:          END IF
   92:          MP1 = M + 1
   93:          DO I = MP1,N,3
   94:             DTEMP = DX(I)
   95:             DX(I) = DY(I)
   96:             DY(I) = DTEMP
   97:             DTEMP = DX(I+1)
   98:             DX(I+1) = DY(I+1)
   99:             DY(I+1) = DTEMP
  100:             DTEMP = DX(I+2)
  101:             DX(I+2) = DY(I+2)
  102:             DY(I+2) = DTEMP
  103:          END DO
  104:       ELSE
  105: *
  106: *       code for unequal increments or equal increments not equal
  107: *         to 1
  108: *
  109:          IX = 1
  110:          IY = 1
  111:          IF (INCX.LT.0) IX = (-N+1)*INCX + 1
  112:          IF (INCY.LT.0) IY = (-N+1)*INCY + 1
  113:          DO I = 1,N
  114:             DTEMP = DX(IX)
  115:             DX(IX) = DY(IY)
  116:             DY(IY) = DTEMP
  117:             IX = IX + INCX
  118:             IY = IY + INCY
  119:          END DO
  120:       END IF
  121:       RETURN
  122:       END