lib/libc/string/swab.c

   1 /*      $NetBSD: swab.c,v 1.18 2011/01/04 17:14:07 martin Exp $ */
   2
   3 /*
   4  * Copyright (c) 1988, 1993
   5  *      The Regents of the University of California.  All rights reserved.
   6  *
   7  * This code is derived from software contributed to Berkeley by
   8  * Jeffrey Mogul.
   9  *
  10  * Redistribution and use in source and binary forms, with or without
  11  * modification, are permitted provided that the following conditions
  12  * are met:
  13  * 1. Redistributions of source code must retain the above copyright
  14  *    notice, this list of conditions and the following disclaimer.
  15  * 2. Redistributions in binary form must reproduce the above copyright
  16  *    notice, this list of conditions and the following disclaimer in the
  17  *    documentation and/or other materials provided with the distribution.
  18  * 3. Neither the name of the University nor the names of its contributors
  19  *    may be used to endorse or promote products derived from this software
  20  *    without specific prior written permission.
  21  *
  22  * THIS SOFTWARE IS PROVIDED BY THE REGENTS AND CONTRIBUTORS ``AS IS'' AND
  23  * ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
  24  * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
  25  * ARE DISCLAIMED.  IN NO EVENT SHALL THE REGENTS OR CONTRIBUTORS BE LIABLE
  26  * FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
  27  * DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
  28  * OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
  29  * HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
  30  * LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
  31  * OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
  32  * SUCH DAMAGE.
  33  */
  34
  35 #include <sys/cdefs.h>
  36 #if defined(LIBC_SCCS) && !defined(lint)
  37 #if 0
  38 static char sccsid[] = "@(#)swab.c      8.1 (Berkeley) 6/4/93";
  39 #else
  40 __RCSID("$NetBSD: swab.c,v 1.18 2011/01/04 17:14:07 martin Exp $");
  41 #endif
  42 #endif /* LIBC_SCCS and not lint */
  43
  44 #include <assert.h>
  45 #include <unistd.h>
  46
  47 void
  48 swab(const void * __restrict from, void * __restrict to, ssize_t len)
  49 {
  50         char temp;
  51         const char *fp;
  52         char *tp;
  53
  54         if (len <= 1)
  55                 return;
  56
  57         _DIAGASSERT(from != NULL);
  58         _DIAGASSERT(to != NULL);
  59
  60         len /= 2;
  61         fp = (const char *)from;
  62         tp = (char *)to;
  63 #define STEP    temp = *fp++,*tp++ = *fp++,*tp++ = temp
  64
  65         if (__predict_false(len == 1)) {
  66                 STEP;
  67                 return;
  68         }
  69
  70         /* round to multiple of 8 */
  71         while ((--len % 8) != 0)
  72                 STEP;
  73         len /= 8;
  74         if (len == 0)
  75                 return;
  76         while (len-- != 0) {
  77                 STEP; STEP; STEP; STEP;
  78                 STEP; STEP; STEP; STEP;
  79         }
  80 }