*> \brief \b DSWAP * * =========== DOCUMENTATION =========== * * Online html documentation available at * http://www.netlib.org/lapack/explore-html/ * * Definition: * =========== * * SUBROUTINE DSWAP(N,DX,INCX,DY,INCY) * * .. Scalar Arguments .. * INTEGER INCX,INCY,N * .. * .. Array Arguments .. * DOUBLE PRECISION DX(*),DY(*) * .. * * *> \par Purpose: * ============= *> *> \verbatim *> *> DSWAP interchanges two vectors. *> uses unrolled loops for increments equal to 1. *> \endverbatim * * Arguments: * ========== * *> \param[in] N *> \verbatim *> N is INTEGER *> number of elements in input vector(s) *> \endverbatim *> *> \param[in,out] DX *> \verbatim *> DX is DOUBLE PRECISION array, dimension ( 1 + ( N - 1 )*abs( INCX ) ) *> \endverbatim *> *> \param[in] INCX *> \verbatim *> INCX is INTEGER *> storage spacing between elements of DX *> \endverbatim *> *> \param[in,out] DY *> \verbatim *> DY is DOUBLE PRECISION array, dimension ( 1 + ( N - 1 )*abs( INCY ) ) *> \endverbatim *> *> \param[in] INCY *> \verbatim *> INCY is INTEGER *> storage spacing between elements of DY *> \endverbatim * * Authors: * ======== * *> \author Univ. of Tennessee *> \author Univ. of California Berkeley *> \author Univ. of Colorado Denver *> \author NAG Ltd. * *> \date December 2016 * *> \ingroup double_blas_level1 * *> \par Further Details: * ===================== *> *> \verbatim *> *> jack dongarra, linpack, 3/11/78. *> modified 12/3/93, array(1) declarations changed to array(*) *> \endverbatim *> * ===================================================================== SUBROUTINE DSWAP(N,DX,INCX,DY,INCY) * * -- Reference BLAS level1 routine (version 3.7.0) -- * -- Reference BLAS is a software package provided by Univ. of Tennessee, -- * -- Univ. of California Berkeley, Univ. of Colorado Denver and NAG Ltd..-- * December 2016 * * .. Scalar Arguments .. INTEGER INCX,INCY,N * .. * .. Array Arguments .. DOUBLE PRECISION DX(*),DY(*) * .. * * ===================================================================== * * .. Local Scalars .. DOUBLE PRECISION DTEMP INTEGER I,IX,IY,M,MP1 * .. * .. Intrinsic Functions .. INTRINSIC MOD * .. IF (N.LE.0) RETURN IF (INCX.EQ.1 .AND. INCY.EQ.1) THEN * * code for both increments equal to 1 * * * clean-up loop * M = MOD(N,3) IF (M.NE.0) THEN DO I = 1,M DTEMP = DX(I) DX(I) = DY(I) DY(I) = DTEMP END DO IF (N.LT.3) RETURN END IF MP1 = M + 1 DO I = MP1,N,3 DTEMP = DX(I) DX(I) = DY(I) DY(I) = DTEMP DTEMP = DX(I+1) DX(I+1) = DY(I+1) DY(I+1) = DTEMP DTEMP = DX(I+2) DX(I+2) = DY(I+2) DY(I+2) = DTEMP END DO ELSE * * code for unequal increments or equal increments not equal * to 1 * IX = 1 IY = 1 IF (INCX.LT.0) IX = (-N+1)*INCX + 1 IF (INCY.LT.0) IY = (-N+1)*INCY + 1 DO I = 1,N DTEMP = DX(IX) DX(IX) = DY(IY) DY(IY) = DTEMP IX = IX + INCX IY = IY + INCY END DO END IF RETURN END