SUBROUTINE DAXPY(N,DA,DX,INCX,DY,INCY) * .. Scalar Arguments .. DOUBLE PRECISION DA INTEGER INCX,INCY,N * .. * .. Array Arguments .. DOUBLE PRECISION DX(*),DY(*) * .. * * Purpose * ======= * * DAXPY constant times a vector plus a vector. * uses unrolled loops for increments equal to one. * * Further Details * =============== * * 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 (DA.EQ.0.0d0) 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 DY(I) = DY(I) + DA*DX(I) END DO END IF IF (N.LT.4) RETURN MP1 = M + 1 DO I = MP1,N,4 DY(I) = DY(I) + DA*DX(I) DY(I+1) = DY(I+1) + DA*DX(I+1) DY(I+2) = DY(I+2) + DA*DX(I+2) DY(I+3) = DY(I+3) + DA*DX(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 DY(IY) = DY(IY) + DA*DX(IX) IX = IX + INCX IY = IY + INCY END DO END IF RETURN END