LAPACK  3.5.0
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sswap.f
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1 *> \brief \b SSWAP
2 *
3 * =========== DOCUMENTATION ===========
4 *
5 * Online html documentation available at
6 * http://www.netlib.org/lapack/explore-html/
7 *
8 * Definition:
9 * ===========
10 *
11 * SUBROUTINE SSWAP(N,SX,INCX,SY,INCY)
12 *
13 * .. Scalar Arguments ..
14 * INTEGER INCX,INCY,N
15 * ..
16 * .. Array Arguments ..
17 * REAL SX(*),SY(*)
18 * ..
19 *
20 *
21 *> \par Purpose:
22 * =============
23 *>
24 *> \verbatim
25 *>
26 *> interchanges two vectors.
27 *> uses unrolled loops for increments equal to 1.
28 *> \endverbatim
29 *
30 * Authors:
31 * ========
32 *
33 *> \author Univ. of Tennessee
34 *> \author Univ. of California Berkeley
35 *> \author Univ. of Colorado Denver
36 *> \author NAG Ltd.
37 *
38 *> \date November 2011
39 *
40 *> \ingroup single_blas_level1
41 *
42 *> \par Further Details:
43 * =====================
44 *>
45 *> \verbatim
46 *>
47 *> jack dongarra, linpack, 3/11/78.
48 *> modified 12/3/93, array(1) declarations changed to array(*)
49 *> \endverbatim
50 *>
51 * =====================================================================
52  SUBROUTINE sswap(N,SX,INCX,SY,INCY)
53 *
54 * -- Reference BLAS level1 routine (version 3.4.0) --
55 * -- Reference BLAS is a software package provided by Univ. of Tennessee, --
56 * -- Univ. of California Berkeley, Univ. of Colorado Denver and NAG Ltd..--
57 * November 2011
58 *
59 * .. Scalar Arguments ..
60  INTEGER incx,incy,n
61 * ..
62 * .. Array Arguments ..
63  REAL sx(*),sy(*)
64 * ..
65 *
66 * =====================================================================
67 *
68 * .. Local Scalars ..
69  REAL stemp
70  INTEGER i,ix,iy,m,mp1
71 * ..
72 * .. Intrinsic Functions ..
73  INTRINSIC mod
74 * ..
75  IF (n.LE.0) RETURN
76  IF (incx.EQ.1 .AND. incy.EQ.1) THEN
77 *
78 * code for both increments equal to 1
79 *
80 *
81 * clean-up loop
82 *
83  m = mod(n,3)
84  IF (m.NE.0) THEN
85  DO i = 1,m
86  stemp = sx(i)
87  sx(i) = sy(i)
88  sy(i) = stemp
89  END DO
90  IF (n.LT.3) RETURN
91  END IF
92  mp1 = m + 1
93  DO i = mp1,n,3
94  stemp = sx(i)
95  sx(i) = sy(i)
96  sy(i) = stemp
97  stemp = sx(i+1)
98  sx(i+1) = sy(i+1)
99  sy(i+1) = stemp
100  stemp = sx(i+2)
101  sx(i+2) = sy(i+2)
102  sy(i+2) = stemp
103  END DO
104  ELSE
105 *
106 * code for unequal increments or equal increments not equal
107 * to 1
108 *
109  ix = 1
110  iy = 1
111  IF (incx.LT.0) ix = (-n+1)*incx + 1
112  IF (incy.LT.0) iy = (-n+1)*incy + 1
113  DO i = 1,n
114  stemp = sx(ix)
115  sx(ix) = sy(iy)
116  sy(iy) = stemp
117  ix = ix + incx
118  iy = iy + incy
119  END DO
120  END IF
121  RETURN
122  END