1 /* $NetBSD: swab.c,v 1.20 2022/12/28 15:34:19 riastradh Exp $ */
2
3
4 /*-
5 * Copyright (c) 2022 The NetBSD Foundation, Inc.
6 * All rights reserved.
7 *
8 * Redistribution and use in source and binary forms, with or without
9 * modification, are permitted provided that the following conditions
10 * are met:
11 * 1. Redistributions of source code must retain the above copyright
12 * notice, this list of conditions and the following disclaimer.
13 * 2. Redistributions in binary form must reproduce the above copyright
14 * notice, this list of conditions and the following disclaimer in the
15 * documentation and/or other materials provided with the distribution.
16 *
17 * THIS SOFTWARE IS PROVIDED BY THE NETBSD FOUNDATION, INC. AND CONTRIBUTORS
18 * ``AS IS'' AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED
19 * TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR
20 * PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE FOUNDATION OR CONTRIBUTORS
21 * BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR
22 * CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF
23 * SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS
24 * INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN
25 * CONTRACT, STRICT LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE)
26 * ARISING IN ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE
27 * POSSIBILITY OF SUCH DAMAGE.
28 */
29
30 #include <sys/cdefs.h>
31 #if defined(LIBC_SCCS) && !defined(lint)
32 __RCSID("$NetBSD: swab.c,v 1.20 2022/12/28 15:34:19 riastradh Exp $");
33 #endif
34
35 #include <assert.h>
36 #include <unistd.h>
37
38 void
swab(const void * __restrict src,void * __restrict dst,ssize_t nbytes)39 swab(const void *__restrict src, void *__restrict dst, ssize_t nbytes)
40 {
41 const char *p = src;
42 char *q = dst;
43 size_t n;
44
45 _DIAGASSERT(src != NULL);
46 _DIAGASSERT(dst != NULL);
47
48 if (nbytes <= 1)
49 return;
50
51 /*
52 * Round nbytes/2 down; we ignore the last byte altogether if
53 * nbytes is odd. This way, if the destination array is
54 * uninitialized, sanitizers will recognize the last byte as
55 * still uninitialized and flag it as undefined.
56 */
57 for (n = nbytes/2; n --> 0; p += 2, q += 2) {
58 /*
59 * According to POSIX (2018), the behaviour is
60 * undefined if src and dst overlap. However, there
61 * are uses in-tree (xsrc/external/mit/xfwp/dist/io.c)
62 * that rely on swab(ptr, ptr, n) to do the swabbing
63 * in-place. So make sure this works if src == dst.
64 */
65 const char p0 = p[0], p1 = p[1];
66
67 q[0] = p1;
68 q[1] = p0;
69 }
70 }
71