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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 $
34 #include <machine/endian.h>
36 typedef const void *cvp
;
37 typedef const unsigned char *ustring
;
38 typedef unsigned long ul
;
39 typedef const unsigned long *culp
;
42 * bcmp -- vax cmpc3 instruction
45 bcmp(const void *b1
, const void *b2
, size_t length
)
47 #if BYTE_ORDER == LITTLE_ENDIAN
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.
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.
58 int shl
, shr
, len
= length
;
59 ustring p1
= b1
, p2
= b2
;
66 * align p1 to a longword boundary
68 while ((long)p1
& (sizeof(long) - 1)) {
76 * align p2 to longword boundary and calculate the shift required to
79 shr
= (long)p2
& (sizeof(long) - 1);
81 p2
-= shr
; /* p2 now longword aligned */
82 shr
<<= 3; /* offset in bits */
83 shl
= (sizeof(long) << 3) - shr
;
88 while ((len
-= sizeof(long)) >= 0) {
91 if (*(culp
)p1
!= (va
>> shr
| vb
<< shl
))
97 * At this point, len is between -sizeof(long) and -1,
98 * representing 0 .. sizeof(long)-1 bytes remaining.
100 if (!(len
+= sizeof(long)))
103 len
<<= 3; /* remaining length in bits */
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.
110 return ((((va
>> shr
| ((shl
< len
) ? *(culp
)p2
<< shl
: 0)) ^
111 *(culp
)p1
) & ((1L << len
) - 1)) != 0);
113 /* p1 and p2 have common alignment so no shifting needed */
114 while ((len
-= sizeof(long)) >= 0) {
115 if (*(culp
)p1
!= *(culp
)p2
)
122 * At this point, len is between -sizeof(long) and -1,
123 * representing 0 .. sizeof(long)-1 bytes remaining.
125 if (!(len
+= sizeof(long)))
128 return (((*(culp
)p1
^ *(culp
)p2
)
129 & ((1L << (len
<< 3)) - 1)) != 0);