The Design and Implementation of the FreeBSD Operating System, Second Edition
Now available: The Design and Implementation of the FreeBSD Operating System (Second Edition)


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FreeBSD/Linux Kernel Cross Reference
sys/libkern/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  * $FreeBSD: src/sys/libkern/bcmp.c,v 1.7 2002/08/22 20:08:07 jhb Exp $
   34  */
   35 
   36 #include <sys/libkern.h>
   37 #include <machine/endian.h>
   38 
   39 typedef const void      *cvp;
   40 typedef const unsigned char     *ustring;
   41 typedef unsigned long   ul;
   42 typedef const unsigned long     *culp;
   43 
   44 /*
   45  * bcmp -- vax cmpc3 instruction
   46  */
   47 int
   48 bcmp(b1, b2, length)
   49         const void *b1, *b2;
   50         register size_t length;
   51 {
   52 #if BYTE_ORDER == LITTLE_ENDIAN
   53         /*
   54          * The following code is endian specific.  Changing it from
   55          * little-endian to big-endian is fairly trivial, but making
   56          * it do both is more difficult.
   57          *
   58          * Note that this code will reference the entire longword which
   59          * includes the final byte to compare.  I don't believe this is
   60          * a problem since AFAIK, objects are not protected at smaller
   61          * than longword boundaries.
   62          */
   63         int     shl, shr, len = length;
   64         ustring p1 = b1, p2 = b2;
   65         ul      va, vb;
   66 
   67         if (len == 0)
   68                 return (0);
   69 
   70         /*
   71          * align p1 to a longword boundary
   72          */
   73         while ((long)p1 & (sizeof(long) - 1)) {
   74                 if (*p1++ != *p2++)
   75                         return (1);
   76                 if (--len <= 0)
   77                         return (0);
   78         }
   79 
   80         /*
   81          * align p2 to longword boundary and calculate the shift required to
   82          * align p1 and p2
   83          */
   84         shr = (long)p2 & (sizeof(long) - 1);
   85         if (shr != 0) {
   86                 p2 -= shr;                      /* p2 now longword aligned */
   87                 shr <<= 3;                      /* offset in bits */
   88                 shl = (sizeof(long) << 3) - shr;
   89 
   90                 va = *(culp)p2;
   91                 p2 += sizeof(long);
   92 
   93                 while ((len -= sizeof(long)) >= 0) {
   94                         vb = *(culp)p2;
   95                         p2 += sizeof(long);
   96                         if (*(culp)p1 != (va >> shr | vb << shl))
   97                                 return (1);
   98                         p1 += sizeof(long);
   99                         va = vb;
  100                 }
  101                 /*
  102                  * At this point, len is between -sizeof(long) and -1,
  103                  * representing 0 .. sizeof(long)-1 bytes remaining.
  104                  */
  105                 if (!(len += sizeof(long)))
  106                         return (0);
  107 
  108                 len <<= 3;              /* remaining length in bits */
  109                 /*
  110                  * The following is similar to the `if' condition
  111                  * inside the above while loop.  The ?: is necessary
  112                  * to avoid accessing the longword after the longword
  113                  * containing the last byte to be compared.
  114                  */
  115                 return ((((va >> shr | ((shl < len) ? *(culp)p2 << shl : 0)) ^
  116                     *(culp)p1) & ((1L << len) - 1)) != 0);
  117         } else {
  118                 /* p1 and p2 have common alignment so no shifting needed */
  119                 while ((len -= sizeof(long)) >= 0) {
  120                         if (*(culp)p1 != *(culp)p2)
  121                                 return (1);
  122                         p1 += sizeof(long);
  123                         p2 += sizeof(long);
  124                 }
  125 
  126                 /*
  127                  * At this point, len is between -sizeof(long) and -1,
  128                  * representing 0 .. sizeof(long)-1 bytes remaining.
  129                  */
  130                 if (!(len += sizeof(long)))
  131                         return (0);
  132 
  133                 return (((*(culp)p1 ^ *(culp)p2)
  134                          & ((1L << (len << 3)) - 1)) != 0);
  135         }
  136 #else
  137         register char *p1, *p2;
  138 
  139         if (length == 0)
  140                 return(0);
  141         p1 = (char *)b1;
  142         p2 = (char *)b2;
  143         do
  144                 if (*p1++ != *p2++)
  145                         break;
  146         while (--length);
  147         return(length);
  148 #endif
  149 }

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