1 /* Copyright (c) 2013 Yaakov Selkowitz <yselkowi@redhat.com> */
2 /*
3 FUNCTION
4 <<rawmemchr>>---find character in memory
5
6 INDEX
7 rawmemchr
8
9 SYNOPSIS
10 #include <string.h>
11 void *rawmemchr(const void *<[src]>, int <[c]>);
12
13 DESCRIPTION
14 This function searches memory starting at <<*<[src]>>> for the
15 character <[c]>. The search only ends with the first occurrence
16 of <[c]>; in particular, <<NUL>> does not terminate the search.
17 No bounds checking is performed, so this function should only
18 be used when it is certain that the character <[c]> will be found.
19
20 RETURNS
21 A pointer to the first occurance of character <[c]>.
22
23 PORTABILITY
24 <<rawmemchr>> is a GNU extension.
25
26 <<rawmemchr>> requires no supporting OS subroutines.
27
28 QUICKREF
29 rawmemchr
30 */
31
32 #include <_ansi.h>
33 #include <string.h>
34 #include <limits.h>
35 #include <stdint.h>
36
37 /* Nonzero if X is not aligned on a "long" boundary. */
38 #define UNALIGNED(X) ((uintptr_t)X & (sizeof (long) - 1))
39
40 /* How many bytes are loaded each iteration of the word copy loop. */
41 #define LBLOCKSIZE (sizeof (long))
42
43 /* Threshhold for punting to the bytewise iterator. */
44 #define TOO_SMALL(LEN) ((LEN) < LBLOCKSIZE)
45
46 #if LONG_MAX == 2147483647L
47 #define DETECTNULL(X) (((X) - 0x01010101) & ~(X) & 0x80808080)
48 #else
49 #if LONG_MAX == 9223372036854775807L
50 /* Nonzero if X (a long int) contains a NULL byte. */
51 #define DETECTNULL(X) (((X) - 0x0101010101010101) & ~(X) & 0x8080808080808080)
52 #else
53 #error long int is not a 32bit or 64bit type.
54 #endif
55 #endif
56
57 #ifndef DETECTNULL
58 #error long int is not a 32bit or 64bit byte
59 #endif
60
61 /* DETECTCHAR returns nonzero if (long)X contains the byte used
62 to fill (long)MASK. */
63 #define DETECTCHAR(X,MASK) (DETECTNULL(X ^ MASK))
64
65 void *
rawmemchr(const void * src_void,int c)66 rawmemchr (const void *src_void,
67 int c)
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 (*src == d)
80 return (void *) src;
81 src++;
82 }
83
84 /* If we get this far, we know that src is word-aligned. */
85 /* The fast code reads the source one word at a time and only
86 performs the bytewise search on word-sized segments if they
87 contain the search character, which is detected by XORing
88 the word-sized segment with a word-sized block of the search
89 character and then detecting for the presence of NUL in the
90 result. */
91 asrc = (unsigned long *) src;
92 mask = d << 8 | d;
93 mask = mask << 16 | mask;
94 for (i = 32; i < LBLOCKSIZE * 8; i <<= 1)
95 mask = (mask << i) | mask;
96
97 while (1)
98 {
99 if (DETECTCHAR (*asrc, mask))
100 break;
101 asrc++;
102 }
103
104 /* We have the matching word, now we resort to a bytewise loop. */
105
106 src = (unsigned char *) asrc;
107
108 #endif /* !PREFER_SIZE_OVER_SPEED && !__OPTIMIZE_SIZE__ */
109
110 while (1)
111 {
112 if (*src == d)
113 return (void *) src;
114 src++;
115 }
116 }
117
