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. 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 
   34 #include <sys/cdefs.h>
   35 __FBSDID("$FreeBSD: releng/5.2/sys/libkern/bcmp.c 116189 2003-06-11 05:37:42Z obrien $");
   36 
   37 #include <sys/libkern.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(b1, b2, length)
   50         const void *b1, *b2;
   51         register size_t length;
   52 {
   53 #if BYTE_ORDER == LITTLE_ENDIAN
   54         /*
   55          * The following code is endian specific.  Changing it from
   56          * little-endian to big-endian is fairly trivial, but making
   57          * it do both is more difficult.
   58          *
   59          * Note that this code will reference the entire longword which
   60          * includes the final byte to compare.  I don't believe this is
   61          * a problem since AFAIK, objects are not protected at smaller
   62          * than longword boundaries.
   63          */
   64         int     shl, shr, len = length;
   65         ustring p1 = b1, p2 = b2;
   66         ul      va, vb;
   67 
   68         if (len == 0)
   69                 return (0);
   70 
   71         /*
   72          * align p1 to a longword boundary
   73          */
   74         while ((long)p1 & (sizeof(long) - 1)) {
   75                 if (*p1++ != *p2++)
   76                         return (1);
   77                 if (--len <= 0)
   78                         return (0);
   79         }
   80 
   81         /*
   82          * align p2 to longword boundary and calculate the shift required to
   83          * align p1 and p2
   84          */
   85         shr = (long)p2 & (sizeof(long) - 1);
   86         if (shr != 0) {
   87                 p2 -= shr;                      /* p2 now longword aligned */
   88                 shr <<= 3;                      /* offset in bits */
   89                 shl = (sizeof(long) << 3) - shr;
   90 
   91                 va = *(culp)p2;
   92                 p2 += sizeof(long);
   93 
   94                 while ((len -= sizeof(long)) >= 0) {
   95                         vb = *(culp)p2;
   96                         p2 += sizeof(long);
   97                         if (*(culp)p1 != (va >> shr | vb << shl))
   98                                 return (1);
   99                         p1 += sizeof(long);
  100                         va = vb;
  101                 }
  102                 /*
  103                  * At this point, len is between -sizeof(long) and -1,
  104                  * representing 0 .. sizeof(long)-1 bytes remaining.
  105                  */
  106                 if (!(len += sizeof(long)))
  107                         return (0);
  108 
  109                 len <<= 3;              /* remaining length in bits */
  110                 /*
  111                  * The following is similar to the `if' condition
  112                  * inside the above while loop.  The ?: is necessary
  113                  * to avoid accessing the longword after the longword
  114                  * containing the last byte to be compared.
  115                  */
  116                 return ((((va >> shr | ((shl < len) ? *(culp)p2 << shl : 0)) ^
  117                     *(culp)p1) & ((1L << len) - 1)) != 0);
  118         } else {
  119                 /* p1 and p2 have common alignment so no shifting needed */
  120                 while ((len -= sizeof(long)) >= 0) {
  121                         if (*(culp)p1 != *(culp)p2)
  122                                 return (1);
  123                         p1 += sizeof(long);
  124                         p2 += sizeof(long);
  125                 }
  126 
  127                 /*
  128                  * At this point, len is between -sizeof(long) and -1,
  129                  * representing 0 .. sizeof(long)-1 bytes remaining.
  130                  */
  131                 if (!(len += sizeof(long)))
  132                         return (0);
  133 
  134                 return (((*(culp)p1 ^ *(culp)p2)
  135                          & ((1L << (len << 3)) - 1)) != 0);
  136         }
  137 #else
  138         register char *p1, *p2;
  139 
  140         if (length == 0)
  141                 return(0);
  142         p1 = (char *)b1;
  143         p2 = (char *)b2;
  144         do
  145                 if (*p1++ != *p2++)
  146                         break;
  147         while (--length);
  148         return(length);
  149 #endif
  150 }

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

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