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    1:       SUBROUTINE DAXPY(N,DA,DX,INCX,DY,INCY)
    2: *     .. Scalar Arguments ..
    3:       DOUBLE PRECISION DA
    4:       INTEGER INCX,INCY,N
    5: *     ..
    6: *     .. Array Arguments ..
    7:       DOUBLE PRECISION DX(*),DY(*)
    8: *     ..
    9: *
   10: *  Purpose
   11: *  =======
   12: *
   13: *     DAXPY constant times a vector plus a vector.
   14: *     uses unrolled loops for increments equal to one.
   15: *
   16: *  Further Details
   17: *  ===============
   18: *
   19: *     jack dongarra, linpack, 3/11/78.
   20: *     modified 12/3/93, array(1) declarations changed to array(*)
   21: *
   22: *  =====================================================================
   23: *
   24: *     .. Local Scalars ..
   25:       INTEGER I,IX,IY,M,MP1
   26: *     ..
   27: *     .. Intrinsic Functions ..
   28:       INTRINSIC MOD
   29: *     ..
   30:       IF (N.LE.0) RETURN
   31:       IF (DA.EQ.0.0d0) RETURN
   32:       IF (INCX.EQ.1 .AND. INCY.EQ.1) THEN
   33: *
   34: *        code for both increments equal to 1
   35: *
   36: *
   37: *        clean-up loop
   38: *
   39:          M = MOD(N,4)
   40:          IF (M.NE.0) THEN
   41:             DO I = 1,M
   42:                DY(I) = DY(I) + DA*DX(I)
   43:             END DO
   44:          END IF
   45:          IF (N.LT.4) RETURN
   46:          MP1 = M + 1
   47:          DO I = MP1,N,4
   48:             DY(I) = DY(I) + DA*DX(I)
   49:             DY(I+1) = DY(I+1) + DA*DX(I+1)
   50:             DY(I+2) = DY(I+2) + DA*DX(I+2)
   51:             DY(I+3) = DY(I+3) + DA*DX(I+3)
   52:          END DO
   53:       ELSE
   54: *
   55: *        code for unequal increments or equal increments
   56: *          not equal to 1
   57: *
   58:          IX = 1
   59:          IY = 1
   60:          IF (INCX.LT.0) IX = (-N+1)*INCX + 1
   61:          IF (INCY.LT.0) IY = (-N+1)*INCY + 1
   62:          DO I = 1,N
   63:           DY(IY) = DY(IY) + DA*DX(IX)
   64:           IX = IX + INCX
   65:           IY = IY + INCY
   66:          END DO
   67:       END IF
   68:       RETURN
   69:       END