1 /*
2 FUNCTION
3 <<strncat>>---concatenate strings
4
5 INDEX
6 strncat
7
8 ANSI_SYNOPSIS
9 #include <string.h>
10 char *strncat(char *restrict <[dst]>, const char *restrict <[src]>,
11 size_t <[length]>);
12
13 TRAD_SYNOPSIS
14 #include <string.h>
15 char *strncat(<[dst]>, <[src]>, <[length]>)
16 char *<[dst]>;
17 char *<[src]>;
18 size_t <[length]>;
19
20 DESCRIPTION
21 <<strncat>> appends not more than <[length]> characters from
22 the string pointed to by <[src]> (including the terminating
23 null character) to the end of the string pointed to by
24 <[dst]>. The initial character of <[src]> overwrites the null
25 character at the end of <[dst]>. A terminating null character
26 is always appended to the result
27
28 WARNINGS
29 Note that a null is always appended, so that if the copy is
30 limited by the <[length]> argument, the number of characters
31 appended to <[dst]> is <<n + 1>>.
32
33 RETURNS
34 This function returns the initial value of <[dst]>
35
36 PORTABILITY
37 <<strncat>> is ANSI C.
38
39 <<strncat>> requires no supporting OS subroutines.
40
41 QUICKREF
42 strncat ansi pure
43 */
44
45 #include <section_config.h>
46 #include <basic_types.h>
47
48 #include <string.h>
49 #include <limits.h>
50
51 /* Nonzero if X is aligned on a "long" boundary. */
52 #define ALIGNED(X) \
53 (((long)X & (sizeof (long) - 1)) == 0)
54
55 #if LONG_MAX == 2147483647L
56 #define DETECTNULL(X) (((X) - 0x01010101) & ~(X) & 0x80808080)
57 #else
58 #if LONG_MAX == 9223372036854775807L
59 /* Nonzero if X (a long int) contains a NULL byte. */
60 #define DETECTNULL(X) (((X) - 0x0101010101010101) & ~(X) & 0x8080808080808080)
61 #else
62 #error long int is not a 32bit or 64bit type.
63 #endif
64 #endif
65
66 #ifndef DETECTNULL
67 #error long int is not a 32bit or 64bit byte
68 #endif
69
70 LIBC_ROM_TEXT_SECTION
71 _LONG_CALL_
_strncat(char * __restrict s1,const char * __restrict s2,size_t n)72 char * _strncat(char *__restrict s1 , const char *__restrict s2 , size_t n)
73 {
74 #if defined(PREFER_SIZE_OVER_SPEED)
75 char *s = s1;
76
77 while (*s1)
78 s1++;
79 while (n-- != 0 && (*s1++ = *s2++))
80 {
81 if (n == 0)
82 *s1 = '\0';
83 }
84
85 return s;
86 #else
87 char *s = s1;
88
89 /* Skip over the data in s1 as quickly as possible. */
90 if (ALIGNED (s1))
91 {
92 unsigned long *aligned_s1 = (unsigned long *)s1;
93 while (!DETECTNULL (*aligned_s1))
94 aligned_s1++;
95
96 s1 = (char *)aligned_s1;
97 }
98
99 while (*s1)
100 s1++;
101
102 /* s1 now points to the its trailing null character, now copy
103 up to N bytes from S2 into S1 stopping if a NULL is encountered
104 in S2.
105
106 It is not safe to use strncpy here since it copies EXACTLY N
107 characters, NULL padding if necessary. */
108 while (n-- != 0 && (*s1++ = *s2++))
109 {
110 if (n == 0)
111 *s1 = '\0';
112 }
113
114 return s;
115 #endif /* not PREFER_SIZE_OVER_SPEED */
116 }
117