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 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