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

     /*-
      * Copyright (c) 1987, 1993
      *      The Regents of the University of California.  All rights reserved.
      *
      * Redistribution and use in source and binary forms, with or without
      * modification, are permitted provided that the following conditions
      * are met:
      * 1. Redistributions of source code must retain the above copyright
      *    notice, this list of conditions and the following disclaimer.
     * 2. Redistributions in binary form must reproduce the above copyright
     *    notice, this list of conditions and the following disclaimer in the
     *    documentation and/or other materials provided with the distribution.
     * 4. Neither the name of the University nor the names of its contributors
     *    may be used to endorse or promote products derived from this software
     *    without specific prior written permission.
     *
     * THIS SOFTWARE IS PROVIDED BY THE REGENTS AND CONTRIBUTORS ``AS IS'' AND
     * ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
     * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
     * ARE DISCLAIMED.  IN NO EVENT SHALL THE REGENTS OR CONTRIBUTORS BE LIABLE
     * FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
     * DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
     * OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
     * HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
     * LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
     * OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
     * SUCH DAMAGE.
     */
    
    #include <sys/cdefs.h>
    __FBSDID("$FreeBSD$");
    
    #include <sys/libkern.h>
    #include <machine/endian.h>
    
    typedef const void      *cvp;
    typedef const unsigned char     *ustring;
    typedef unsigned long   ul;
    typedef const unsigned long     *culp;
    
    /*
     * bcmp -- vax cmpc3 instruction
     */
    int
    bcmp(b1, b2, length)
            const void *b1, *b2;
            register size_t length;
    {
    #if BYTE_ORDER == LITTLE_ENDIAN
            /*
             * The following code is endian specific.  Changing it from
             * little-endian to big-endian is fairly trivial, but making
             * it do both is more difficult.
             *
             * Note that this code will reference the entire longword which
             * includes the final byte to compare.  I don't believe this is
             * a problem since AFAIK, objects are not protected at smaller
             * than longword boundaries.
             */
            int     shl, shr, len = length;
            ustring p1 = b1, p2 = b2;
            ul      va, vb;
    
            if (len == 0)
                    return (0);
    
            /*
             * align p1 to a longword boundary
             */
            while ((long)p1 & (sizeof(long) - 1)) {
                    if (*p1++ != *p2++)
                            return (1);
                    if (--len <= 0)
                            return (0);
            }
    
            /*
             * align p2 to longword boundary and calculate the shift required to
             * align p1 and p2
             */
            shr = (long)p2 & (sizeof(long) - 1);
            if (shr != 0) {
                    p2 -= shr;                      /* p2 now longword aligned */
                    shr <<= 3;                      /* offset in bits */
                    shl = (sizeof(long) << 3) - shr;
    
                    va = *(culp)p2;
                    p2 += sizeof(long);
    
                    while ((len -= sizeof(long)) >= 0) {
                            vb = *(culp)p2;
                            p2 += sizeof(long);
                            if (*(culp)p1 != (va >> shr | vb << shl))
                                    return (1);
                            p1 += sizeof(long);
                            va = vb;
                    }
                    /*
                     * At this point, len is between -sizeof(long) and -1,
                    * representing 0 .. sizeof(long)-1 bytes remaining.
                    */
                   if (!(len += sizeof(long)))
                           return (0);
   
                   len <<= 3;              /* remaining length in bits */
                   /*
                    * The following is similar to the `if' condition
                    * inside the above while loop.  The ?: is necessary
                    * to avoid accessing the longword after the longword
                    * containing the last byte to be compared.
                    */
                   return ((((va >> shr | ((shl < len) ? *(culp)p2 << shl : 0)) ^
                       *(culp)p1) & ((1L << len) - 1)) != 0);
           } else {
                   /* p1 and p2 have common alignment so no shifting needed */
                   while ((len -= sizeof(long)) >= 0) {
                           if (*(culp)p1 != *(culp)p2)
                                   return (1);
                           p1 += sizeof(long);
                           p2 += sizeof(long);
                   }
   
                   /*
                    * At this point, len is between -sizeof(long) and -1,
                    * representing 0 .. sizeof(long)-1 bytes remaining.
                    */
                   if (!(len += sizeof(long)))
                           return (0);
   
                   return (((*(culp)p1 ^ *(culp)p2)
                            & ((1L << (len << 3)) - 1)) != 0);
           }
   #else
           const char *p1, *p2;
   
           if (length == 0)
                   return(0);
           p1 = b1;
           p2 = b2;
           do
                   if (*p1++ != *p2++)
                           break;
           while (--length);
           return(length);
   #endif
   }

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