bcmp.c

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

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FreeBSD/Linux Kernel Cross Reference sys/libkern/bcmp.c

FreeBSD/Linux Kernel Cross Reference
sys/libkern/bcmp.c