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