LAPACK  3.4.1
LAPACK: Linear Algebra PACKage
saxpy.f
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00001 *> \brief \b SAXPY
00002 *
00003 *  =========== DOCUMENTATION ===========
00004 *
00005 * Online html documentation available at 
00006 *            http://www.netlib.org/lapack/explore-html/ 
00007 *
00008 *  Definition:
00009 *  ===========
00010 *
00011 *       SUBROUTINE SAXPY(N,SA,SX,INCX,SY,INCY)
00012 * 
00013 *       .. Scalar Arguments ..
00014 *       REAL SA
00015 *       INTEGER INCX,INCY,N
00016 *       ..
00017 *       .. Array Arguments ..
00018 *       REAL SX(*),SY(*)
00019 *       ..
00020 *  
00021 *
00022 *> \par Purpose:
00023 *  =============
00024 *>
00025 *> \verbatim
00026 *>
00027 *>    SAXPY constant times a vector plus a vector.
00028 *>    uses unrolled loops for increments equal to one.
00029 *> \endverbatim
00030 *
00031 *  Authors:
00032 *  ========
00033 *
00034 *> \author Univ. of Tennessee 
00035 *> \author Univ. of California Berkeley 
00036 *> \author Univ. of Colorado Denver 
00037 *> \author NAG Ltd. 
00038 *
00039 *> \date November 2011
00040 *
00041 *> \ingroup single_blas_level1
00042 *
00043 *> \par Further Details:
00044 *  =====================
00045 *>
00046 *> \verbatim
00047 *>
00048 *>     jack dongarra, linpack, 3/11/78.
00049 *>     modified 12/3/93, array(1) declarations changed to array(*)
00050 *> \endverbatim
00051 *>
00052 *  =====================================================================
00053       SUBROUTINE SAXPY(N,SA,SX,INCX,SY,INCY)
00054 *
00055 *  -- Reference BLAS level1 routine (version 3.4.0) --
00056 *  -- Reference BLAS is a software package provided by Univ. of Tennessee,    --
00057 *  -- Univ. of California Berkeley, Univ. of Colorado Denver and NAG Ltd..--
00058 *     November 2011
00059 *
00060 *     .. Scalar Arguments ..
00061       REAL SA
00062       INTEGER INCX,INCY,N
00063 *     ..
00064 *     .. Array Arguments ..
00065       REAL SX(*),SY(*)
00066 *     ..
00067 *
00068 *  =====================================================================
00069 *
00070 *     .. Local Scalars ..
00071       INTEGER I,IX,IY,M,MP1
00072 *     ..
00073 *     .. Intrinsic Functions ..
00074       INTRINSIC MOD
00075 *     ..
00076       IF (N.LE.0) RETURN
00077       IF (SA.EQ.0.0) RETURN
00078       IF (INCX.EQ.1 .AND. INCY.EQ.1) THEN
00079 *
00080 *        code for both increments equal to 1
00081 *
00082 *
00083 *        clean-up loop
00084 *
00085          M = MOD(N,4)
00086          IF (M.NE.0) THEN
00087             DO I = 1,M
00088                SY(I) = SY(I) + SA*SX(I)
00089             END DO
00090          END IF
00091          IF (N.LT.4) RETURN
00092          MP1 = M + 1
00093          DO I = MP1,N,4
00094             SY(I) = SY(I) + SA*SX(I)
00095             SY(I+1) = SY(I+1) + SA*SX(I+1)
00096             SY(I+2) = SY(I+2) + SA*SX(I+2)
00097             SY(I+3) = SY(I+3) + SA*SX(I+3)
00098          END DO
00099       ELSE
00100 *
00101 *        code for unequal increments or equal increments
00102 *          not equal to 1
00103 *
00104          IX = 1
00105          IY = 1
00106          IF (INCX.LT.0) IX = (-N+1)*INCX + 1
00107          IF (INCY.LT.0) IY = (-N+1)*INCY + 1
00108          DO I = 1,N
00109           SY(IY) = SY(IY) + SA*SX(IX)
00110           IX = IX + INCX
00111           IY = IY + INCY
00112          END DO
00113       END IF
00114       RETURN
00115       END
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