sys/libkern/bcmp.c

   1 /*
   2  * Copyright (c) 1987, 1993
   3  *      The Regents of the University of California.  All rights reserved.
   4  *
   5  * Redistribution and use in source and binary forms, with or without
   6  * modification, are permitted provided that the following conditions
   7  * are met:
   8  * 1. Redistributions of source code must retain the above copyright
   9  *    notice, this list of conditions and the following disclaimer.
  10  * 2. Redistributions in binary form must reproduce the above copyright
  11  *    notice, this list of conditions and the following disclaimer in the
  12  *    documentation and/or other materials provided with the distribution.
  13  * 3. All advertising materials mentioning features or use of this software
  14  *    must display the following acknowledgement:
  15  *      This product includes software developed by the University of
  16  *      California, Berkeley and its contributors.
  17  * 4. Neither the name of the University nor the names of its contributors
  18  *    may be used to endorse or promote products derived from this software
  19  *    without specific prior written permission.
  20  *
  21  * THIS SOFTWARE IS PROVIDED BY THE REGENTS AND CONTRIBUTORS ``AS IS'' AND
  22  * ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
  23  * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
  24  * ARE DISCLAIMED.  IN NO EVENT SHALL THE REGENTS OR CONTRIBUTORS BE LIABLE
  25  * FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
  26  * DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
  27  * OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
  28  * HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
  29  * LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
  30  * OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
  31  * SUCH DAMAGE.
  32  *
  33  * $FreeBSD: src/sys/libkern/bcmp.c,v 1.6 1999/08/28 00:46:31 peter Exp $
  34  * $DragonFly: src/sys/libkern/bcmp.c,v 1.4 2005/01/04 05:27:47 cpressey Exp $
  35  */
  36
  37 #include <string.h>
  38 #include <machine/endian.h>
  39
  40 typedef const void              *cvp;
  41 typedef const unsigned char     *ustring;
  42 typedef unsigned long           ul;
  43 typedef const unsigned long     *culp;
  44
  45 /*
  46  * bcmp -- vax cmpc3 instruction
  47  */
  48 int
  49 bcmp(const void *b1, const void *b2, size_t length)
  50 {
  51 #if BYTE_ORDER == LITTLE_ENDIAN
  52         /*
  53          * The following code is endian specific.  Changing it from
  54          * little-endian to big-endian is fairly trivial, but making
  55          * it do both is more difficult.
  56          *
  57          * Note that this code will reference the entire longword which
  58          * includes the final byte to compare.  I don't believe this is
  59          * a problem since AFAIK, objects are not protected at smaller
  60          * than longword boundaries.
  61          */
  62         int     shl, shr, len = length;
  63         ustring p1 = b1, p2 = b2;
  64         ul      va, vb;
  65
  66         if (len == 0)
  67                 return (0);
  68
  69         /*
  70          * align p1 to a longword boundary
  71          */
  72         while ((long)p1 & (sizeof(long) - 1)) {
  73                 if (*p1++ != *p2++)
  74                         return (1);
  75                 if (--len <= 0)
  76                         return (0);
  77         }
  78
  79         /*
  80          * align p2 to longword boundary and calculate the shift required to
  81          * align p1 and p2
  82          */
  83         shr = (long)p2 & (sizeof(long) - 1);
  84         if (shr != 0) {
  85                 p2 -= shr;                      /* p2 now longword aligned */
  86                 shr <<= 3;                      /* offset in bits */
  87                 shl = (sizeof(long) << 3) - shr;
  88
  89                 va = *(culp)p2;
  90                 p2 += sizeof(long);
  91
  92                 while ((len -= sizeof(long)) >= 0) {
  93                         vb = *(culp)p2;
  94                         p2 += sizeof(long);
  95                         if (*(culp)p1 != (va >> shr | vb << shl))
  96                                 return (1);
  97                         p1 += sizeof(long);
  98                         va = vb;
  99                 }
 100                 /*
 101                  * At this point, len is between -sizeof(long) and -1,
 102                  * representing 0 .. sizeof(long)-1 bytes remaining.
 103                  */
 104                 if (!(len += sizeof(long)))
 105                         return (0);
 106
 107                 len <<= 3;              /* remaining length in bits */
 108                 /*
 109                  * The following is similar to the `if' condition
 110                  * inside the above while loop.  The ?: is necessary
 111                  * to avoid accessing the longword after the longword
 112                  * containing the last byte to be compared.
 113                  */
 114                 return ((((va >> shr | ((shl < len) ? *(culp)p2 << shl : 0)) ^
 115                     *(culp)p1) & ((1L << len) - 1)) != 0);
 116         } else {
 117                 /* p1 and p2 have common alignment so no shifting needed */
 118                 while ((len -= sizeof(long)) >= 0) {
 119                         if (*(culp)p1 != *(culp)p2)
 120                                 return (1);
 121                         p1 += sizeof(long);
 122                         p2 += sizeof(long);
 123                 }
 124
 125                 /*
 126                  * At this point, len is between -sizeof(long) and -1,
 127                  * representing 0 .. sizeof(long)-1 bytes remaining.
 128                  */
 129                 if (!(len += sizeof(long)))
 130                         return (0);
 131
 132                 return (((*(culp)p1 ^ *(culp)p2)
 133                          & ((1L << (len << 3)) - 1)) != 0);
 134         }
 135 #else
 136         char *p1, *p2;
 137
 138         if (length == 0)
 139                 return(0);
 140         p1 = (char *)b1;
 141         p2 = (char *)b2;
 142         do
 143                 if (*p1++ != *p2++)
 144                         break;
 145         while (--length);
 146         return(length);
 147 #endif
 148 }