01:       SUBROUTINE SSWAP(N,SX,INCX,SY,INCY)
02: *     .. Scalar Arguments ..
03:       INTEGER INCX,INCY,N
04: *     ..
05: *     .. Array Arguments ..
06:       REAL SX(*),SY(*)
07: *     ..
08: *
09: *  Purpose
10: *  =======
11: *
12: *     interchanges two vectors.
13: *     uses unrolled loops for increments equal to 1.
14: *     jack dongarra, linpack, 3/11/78.
15: *     modified 12/3/93, array(1) declarations changed to array(*)
16: *
17: *
18: *     .. Local Scalars ..
19:       REAL STEMP
20:       INTEGER I,IX,IY,M,MP1
21: *     ..
22: *     .. Intrinsic Functions ..
23:       INTRINSIC MOD
24: *     ..
25:       IF (N.LE.0) RETURN
26:       IF (INCX.EQ.1 .AND. INCY.EQ.1) GO TO 20
27: *
28: *       code for unequal increments or equal increments not equal
29: *         to 1
30: *
31:       IX = 1
32:       IY = 1
33:       IF (INCX.LT.0) IX = (-N+1)*INCX + 1
34:       IF (INCY.LT.0) IY = (-N+1)*INCY + 1
35:       DO 10 I = 1,N
36:           STEMP = SX(IX)
37:           SX(IX) = SY(IY)
38:           SY(IY) = STEMP
39:           IX = IX + INCX
40:           IY = IY + INCY
41:    10 CONTINUE
42:       RETURN
43: *
44: *       code for both increments equal to 1
45: *
46: *
47: *       clean-up loop
48: *
49:    20 M = MOD(N,3)
50:       IF (M.EQ.0) GO TO 40
51:       DO 30 I = 1,M
52:           STEMP = SX(I)
53:           SX(I) = SY(I)
54:           SY(I) = STEMP
55:    30 CONTINUE
56:       IF (N.LT.3) RETURN
57:    40 MP1 = M + 1
58:       DO 50 I = MP1,N,3
59:           STEMP = SX(I)
60:           SX(I) = SY(I)
61:           SY(I) = STEMP
62:           STEMP = SX(I+1)
63:           SX(I+1) = SY(I+1)
64:           SY(I+1) = STEMP
65:           STEMP = SX(I+2)
66:           SX(I+2) = SY(I+2)
67:           SY(I+2) = STEMP
68:    50 CONTINUE
69:       RETURN
70:       END
71: