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
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