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) GO TO 20
33: *
34: * code for unequal increments or equal increments
35: * not equal to 1
36: *
37: IX = 1
38: IY = 1
39: IF (INCX.LT.0) IX = (-N+1)*INCX + 1
40: IF (INCY.LT.0) IY = (-N+1)*INCY + 1
41: DO 10 I = 1,N
42: DY(IY) = DY(IY) + DA*DX(IX)
43: IX = IX + INCX
44: IY = IY + INCY
45: 10 CONTINUE
46: RETURN
47: *
48: * code for both increments equal to 1
49: *
50: *
51: * clean-up loop
52: *
53: 20 M = MOD(N,4)
54: IF (M.EQ.0) GO TO 40
55: DO 30 I = 1,M
56: DY(I) = DY(I) + DA*DX(I)
57: 30 CONTINUE
58: IF (N.LT.4) RETURN
59: 40 MP1 = M + 1
60: DO 50 I = MP1,N,4
61: DY(I) = DY(I) + DA*DX(I)
62: DY(I+1) = DY(I+1) + DA*DX(I+1)
63: DY(I+2) = DY(I+2) + DA*DX(I+2)
64: DY(I+3) = DY(I+3) + DA*DX(I+3)
65: 50 CONTINUE
66: RETURN
67: END
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