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SUBROUTINE DAXPY(N,DA,DX,INCX,DY,INCY)
* .. Scalar Arguments ..
DOUBLE PRECISION DA
INTEGER INCX,INCY,N
* ..
* .. Array Arguments ..
DOUBLE PRECISION DX(*),DY(*)
* ..
*
* Purpose
* =======
*
* constant times a vector plus a vector.
* uses unrolled loops 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 (DA.EQ.0.0d0) 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
DY(IY) = DY(IY) + DA*DX(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
DY(I) = DY(I) + DA*DX(I)
30 CONTINUE
IF (N.LT.4) RETURN
40 MP1 = M + 1
DO 50 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)
50 CONTINUE
RETURN
END
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