OpenBLAS/lapack-netlib/BLAS/SRC/saxpy.f

*> \brief \b SAXPY
*
*  =========== DOCUMENTATION ===========
*
* Online html documentation available at
*            http://www.netlib.org/lapack/explore-html/
*
*  Definition:
*  ===========
*
*       SUBROUTINE SAXPY(N,SA,SX,INCX,SY,INCY)
*
*       .. Scalar Arguments ..
*       REAL SA
*       INTEGER INCX,INCY,N
*       ..
*       .. Array Arguments ..
*       REAL SX(*),SY(*)
*       ..
*
*
*> \par Purpose:
*  =============
*>
*> \verbatim
*>
*>    SAXPY constant times a vector plus a vector.
*>    uses unrolled loops for increments equal to one.
*> \endverbatim
*
*  Arguments:
*  ==========
*
*> \param[in] N
*> \verbatim
*>          N is INTEGER
*>         number of elements in input vector(s)
*> \endverbatim
*>
*> \param[in] SA
*> \verbatim
*>          SA is REAL
*>           On entry, SA specifies the scalar alpha.
*> \endverbatim
*>
*> \param[in] SX
*> \verbatim
*>          SX is REAL array, dimension ( 1 + ( N - 1 )*abs( INCX ) )
*> \endverbatim
*>
*> \param[in] INCX
*> \verbatim
*>          INCX is INTEGER
*>         storage spacing between elements of SX
*> \endverbatim
*>
*> \param[in,out] SY
*> \verbatim
*>          SY is REAL array, dimension ( 1 + ( N - 1 )*abs( INCY ) )
*> \endverbatim
*>
*> \param[in] INCY
*> \verbatim
*>          INCY is INTEGER
*>         storage spacing between elements of SY
*> \endverbatim
*
*  Authors:
*  ========
*
*> \author Univ. of Tennessee
*> \author Univ. of California Berkeley
*> \author Univ. of Colorado Denver
*> \author NAG Ltd.
*
*> \date November 2017
*
*> \ingroup single_blas_level1
*
*> \par Further Details:
*  =====================
*>
*> \verbatim
*>
*>     jack dongarra, linpack, 3/11/78.
*>     modified 12/3/93, array(1) declarations changed to array(*)
*> \endverbatim
*>
*  =====================================================================
      SUBROUTINE SAXPY(N,SA,SX,INCX,SY,INCY)
*
*  -- Reference BLAS level1 routine (version 3.8.0) --
*  -- Reference BLAS is a software package provided by Univ. of Tennessee,    --
*  -- Univ. of California Berkeley, Univ. of Colorado Denver and NAG Ltd..--
*     November 2017
*
*     .. Scalar Arguments ..
      REAL SA
      INTEGER INCX,INCY,N
*     ..
*     .. Array Arguments ..
      REAL SX(*),SY(*)
*     ..
*
*  =====================================================================
*
*     .. Local Scalars ..
      INTEGER I,IX,IY,M,MP1
*     ..
*     .. Intrinsic Functions ..
      INTRINSIC MOD
*     ..
      IF (N.LE.0) RETURN
      IF (SA.EQ.0.0) RETURN
      IF (INCX.EQ.1 .AND. INCY.EQ.1) THEN
*
*        code for both increments equal to 1
*
*
*        clean-up loop
*
         M = MOD(N,4)
         IF (M.NE.0) THEN
            DO I = 1,M
               SY(I) = SY(I) + SA*SX(I)
            END DO
         END IF
         IF (N.LT.4) RETURN
         MP1 = M + 1
         DO I = MP1,N,4
            SY(I) = SY(I) + SA*SX(I)
            SY(I+1) = SY(I+1) + SA*SX(I+1)
            SY(I+2) = SY(I+2) + SA*SX(I+2)
            SY(I+3) = SY(I+3) + SA*SX(I+3)
         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
          SY(IY) = SY(IY) + SA*SX(IX)
          IX = IX + INCX
          IY = IY + INCY
         END DO
      END IF
      RETURN
      END