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33 * $FreeBSD: src/sys/libkern/bcmp.c,v 1.6 1999/08/28 00:46:31 peter Exp $
34 * $DragonFly: src/sys/libkern/bcmp.c,v 1.2 2003/06/17 04:28:42 dillon Exp $
38 #include <machine/endian.h>
40 typedef const void *cvp;
41 typedef const unsigned char *ustring;
42 typedef unsigned long ul;
43 typedef const unsigned long *culp;
46 * bcmp -- vax cmpc3 instruction
51 register size_t length;
53 #if BYTE_ORDER == LITTLE_ENDIAN
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.
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.
64 int shl, shr, len = length;
65 ustring p1 = b1, p2 = b2;
72 * align p1 to a longword boundary
74 while ((long)p1 & (sizeof(long) - 1)) {
82 * align p2 to longword boundary and calculate the shift required to
85 shr = (long)p2 & (sizeof(long) - 1);
87 p2 -= shr; /* p2 now longword aligned */
88 shr <<= 3; /* offset in bits */
89 shl = (sizeof(long) << 3) - shr;
94 while ((len -= sizeof(long)) >= 0) {
97 if (*(culp)p1 != (va >> shr | vb << shl))
103 * At this point, len is between -sizeof(long) and -1,
104 * representing 0 .. sizeof(long)-1 bytes remaining.
106 if (!(len += sizeof(long)))
109 len <<= 3; /* remaining length in bits */
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.
116 return ((((va >> shr | ((shl < len) ? *(culp)p2 << shl : 0)) ^
117 *(culp)p1) & ((1L << len) - 1)) != 0);
119 /* p1 and p2 have common alignment so no shifting needed */
120 while ((len -= sizeof(long)) >= 0) {
121 if (*(culp)p1 != *(culp)p2)
128 * At this point, len is between -sizeof(long) and -1,
129 * representing 0 .. sizeof(long)-1 bytes remaining.
131 if (!(len += sizeof(long)))
134 return (((*(culp)p1 ^ *(culp)p2)
135 & ((1L << (len << 3)) - 1)) != 0);
138 register char *p1, *p2;