saxpy.f

          SUBROUTINE SAXPY(N,SA,SX,INCX,SY,INCY)
    *     .. Scalar Arguments ..
          REAL SA
          INTEGER INCX,INCY,N
    *     ..
    *     .. Array Arguments ..
          REAL SX(*),SY(*)
    *     ..
    *
    *  Purpose
    *  =======
    *
    *     SAXPY constant times a vector plus a vector.
    *     uses unrolled loop for increments equal to one.
    *     jack dongarra, linpack, 3/11/78.
    *     modified 12/3/93, array(1) declarations changed to array(*)
    *
    *
    *     .. 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) GO TO 20
    *
    *        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 10 I = 1,N
              SY(IY) = SY(IY) + SA*SX(IX)
              IX = IX + INCX
              IY = IY + INCY
       10 CONTINUE
          RETURN
    *
    *        code for both increments equal to 1
    *
    *
    *        clean-up loop
    *
       20 M = MOD(N,4)
          IF (M.EQ.0) GO TO 40
          DO 30 I = 1,M
              SY(I) = SY(I) + SA*SX(I)
       30 CONTINUE
          IF (N.LT.4) RETURN
       40 MP1 = M + 1
          DO 50 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)
       50 CONTINUE
          RETURN
          END