1 | /* |
---|
2 | FUNCTION |
---|
3 | <<memchr>>---find character in memory |
---|
4 | |
---|
5 | INDEX |
---|
6 | memchr |
---|
7 | |
---|
8 | SYNOPSIS |
---|
9 | #include <string.h> |
---|
10 | void *memchr(const void *<[src]>, int <[c]>, size_t <[length]>); |
---|
11 | |
---|
12 | DESCRIPTION |
---|
13 | This function searches memory starting at <<*<[src]>>> for the |
---|
14 | character <[c]>. The search only ends with the first |
---|
15 | occurrence of <[c]>, or after <[length]> characters; in |
---|
16 | particular, <<NUL>> does not terminate the search. |
---|
17 | |
---|
18 | RETURNS |
---|
19 | If the character <[c]> is found within <[length]> characters |
---|
20 | of <<*<[src]>>>, a pointer to the character is returned. If |
---|
21 | <[c]> is not found, then <<NULL>> is returned. |
---|
22 | |
---|
23 | PORTABILITY |
---|
24 | <<memchr>> is ANSI C. |
---|
25 | |
---|
26 | <<memchr>> requires no supporting OS subroutines. |
---|
27 | |
---|
28 | QUICKREF |
---|
29 | memchr ansi pure |
---|
30 | */ |
---|
31 | |
---|
32 | #include <_ansi.h> |
---|
33 | #include <string.h> |
---|
34 | #include <limits.h> |
---|
35 | |
---|
36 | /* Nonzero if either X or Y is not aligned on a "long" boundary. */ |
---|
37 | #define UNALIGNED(X) ((long)X & (sizeof (long) - 1)) |
---|
38 | |
---|
39 | /* How many bytes are loaded each iteration of the word copy loop. */ |
---|
40 | #define LBLOCKSIZE (sizeof (long)) |
---|
41 | |
---|
42 | /* Threshhold for punting to the bytewise iterator. */ |
---|
43 | #define TOO_SMALL(LEN) ((LEN) < LBLOCKSIZE) |
---|
44 | |
---|
45 | #if LONG_MAX == 2147483647L |
---|
46 | #define DETECTNULL(X) (((X) - 0x01010101) & ~(X) & 0x80808080) |
---|
47 | #else |
---|
48 | #if LONG_MAX == 9223372036854775807L |
---|
49 | /* Nonzero if X (a long int) contains a NULL byte. */ |
---|
50 | #define DETECTNULL(X) (((X) - 0x0101010101010101) & ~(X) & 0x8080808080808080) |
---|
51 | #else |
---|
52 | #error long int is not a 32bit or 64bit type. |
---|
53 | #endif |
---|
54 | #endif |
---|
55 | |
---|
56 | #ifndef DETECTNULL |
---|
57 | #error long int is not a 32bit or 64bit byte |
---|
58 | #endif |
---|
59 | |
---|
60 | /* DETECTCHAR returns nonzero if (long)X contains the byte used |
---|
61 | to fill (long)MASK. */ |
---|
62 | #define DETECTCHAR(X,MASK) (DETECTNULL(X ^ MASK)) |
---|
63 | |
---|
64 | void * |
---|
65 | memchr (const void *src_void, |
---|
66 | int c, |
---|
67 | size_t length) |
---|
68 | { |
---|
69 | const unsigned char *src = (const unsigned char *) src_void; |
---|
70 | unsigned char d = c; |
---|
71 | |
---|
72 | #if !defined(PREFER_SIZE_OVER_SPEED) && !defined(__OPTIMIZE_SIZE__) |
---|
73 | unsigned long *asrc; |
---|
74 | unsigned long mask; |
---|
75 | unsigned int i; |
---|
76 | |
---|
77 | while (UNALIGNED (src)) |
---|
78 | { |
---|
79 | if (!length--) |
---|
80 | return NULL; |
---|
81 | if (*src == d) |
---|
82 | return (void *) src; |
---|
83 | src++; |
---|
84 | } |
---|
85 | |
---|
86 | if (!TOO_SMALL (length)) |
---|
87 | { |
---|
88 | /* If we get this far, we know that length is large and src is |
---|
89 | word-aligned. */ |
---|
90 | /* The fast code reads the source one word at a time and only |
---|
91 | performs the bytewise search on word-sized segments if they |
---|
92 | contain the search character, which is detected by XORing |
---|
93 | the word-sized segment with a word-sized block of the search |
---|
94 | character and then detecting for the presence of NUL in the |
---|
95 | result. */ |
---|
96 | asrc = (unsigned long *) src; |
---|
97 | mask = d << 8 | d; |
---|
98 | mask = mask << 16 | mask; |
---|
99 | for (i = 32; i < LBLOCKSIZE * 8; i <<= 1) |
---|
100 | mask = (mask << i) | mask; |
---|
101 | |
---|
102 | while (length >= LBLOCKSIZE) |
---|
103 | { |
---|
104 | if (DETECTCHAR (*asrc, mask)) |
---|
105 | break; |
---|
106 | length -= LBLOCKSIZE; |
---|
107 | asrc++; |
---|
108 | } |
---|
109 | |
---|
110 | /* If there are fewer than LBLOCKSIZE characters left, |
---|
111 | then we resort to the bytewise loop. */ |
---|
112 | |
---|
113 | src = (unsigned char *) asrc; |
---|
114 | } |
---|
115 | |
---|
116 | #endif /* not PREFER_SIZE_OVER_SPEED */ |
---|
117 | |
---|
118 | while (length--) |
---|
119 | { |
---|
120 | if (*src == d) |
---|
121 | return (void *) src; |
---|
122 | src++; |
---|
123 | } |
---|
124 | |
---|
125 | return NULL; |
---|
126 | } |
---|