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