1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
63
64
65
66
67
68
69
70
71
72
73
74
75
76
77
78
79
80
81
82
83
84
85
86
87
88
89
90
91
92
93
94
95
96
97
98
99
100
101
102
103
104
105
106
107
108
109
110
111
112
113
|
/*
FUNCTION
<<memcmp>>---compare two memory areas
INDEX
memcmp
ANSI_SYNOPSIS
#include <string.h>
int memcmp(const void *<[s1]>, const void *<[s2]>, size_t <[n]>);
TRAD_SYNOPSIS
#include <string.h>
int memcmp(<[s1]>, <[s2]>, <[n]>)
void *<[s1]>;
void *<[s2]>;
size_t <[n]>;
DESCRIPTION
This function compares not more than <[n]> characters of the
object pointed to by <[s1]> with the object pointed to by <[s2]>.
RETURNS
The function returns an integer greater than, equal to or
less than zero according to whether the object pointed to by
<[s1]> is greater than, equal to or less than the object
pointed to by <[s2]>.
PORTABILITY
<<memcmp>> is ANSI C.
<<memcmp>> requires no supporting OS subroutines.
QUICKREF
memcmp ansi pure
*/
#include <string.h>
#include "_ansi.h" /* for _DEFUN */
/* Nonzero if either X or Y is not aligned on a "long" boundary. */
#define UNALIGNED(X, Y) \
(((long)X & (sizeof (long) - 1)) | ((long)Y & (sizeof (long) - 1)))
/* How many bytes are copied each iteration of the word copy loop. */
#define LBLOCKSIZE (sizeof (long))
/* Threshhold for punting to the byte copier. */
#define TOO_SMALL(LEN) ((LEN) < LBLOCKSIZE)
int
_DEFUN (memcmp, (m1, m2, n),
_CONST _PTR m1 _AND
_CONST _PTR m2 _AND
size_t n)
{
#if defined(PREFER_SIZE_OVER_SPEED) || defined(__OPTIMIZE_SIZE__)
unsigned char *s1 = (unsigned char *) m1;
unsigned char *s2 = (unsigned char *) m2;
while (n--)
{
if (*s1 != *s2)
{
return *s1 - *s2;
}
s1++;
s2++;
}
return 0;
#else
unsigned char *s1 = (unsigned char *) m1;
unsigned char *s2 = (unsigned char *) m2;
unsigned long *a1;
unsigned long *a2;
/* If the size is too small, or either pointer is unaligned,
then we punt to the byte compare loop. Hopefully this will
not turn up in inner loops. */
if (!TOO_SMALL(n) && !UNALIGNED(s1,s2))
{
/* Otherwise, load and compare the blocks of memory one
word at a time. */
a1 = (unsigned long*) s1;
a2 = (unsigned long*) s2;
while (n >= LBLOCKSIZE)
{
if (*a1 != *a2)
break;
a1++;
a2++;
n -= LBLOCKSIZE;
}
/* check m mod LBLOCKSIZE remaining characters */
s1 = (unsigned char*)a1;
s2 = (unsigned char*)a2;
}
while (n--)
{
if (*s1 != *s2)
return *s1 - *s2;
s1++;
s2++;
}
return 0;
#endif /* not PREFER_SIZE_OVER_SPEED */
}
|
