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. 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 }