109 lines
2.4 KiB
C
109 lines
2.4 KiB
C
/*
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FUNCTION
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<<strncat>>---concatenate strings
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INDEX
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strncat
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SYNOPSIS
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#include <string.h>
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char *strncat(char *restrict <[dst]>, const char *restrict <[src]>,
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size_t <[length]>);
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DESCRIPTION
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<<strncat>> appends not more than <[length]> characters from
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the string pointed to by <[src]> (including the terminating
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null character) to the end of the string pointed to by
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<[dst]>. The initial character of <[src]> overwrites the null
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character at the end of <[dst]>. A terminating null character
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is always appended to the result
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WARNINGS
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Note that a null is always appended, so that if the copy is
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limited by the <[length]> argument, the number of characters
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appended to <[dst]> is <<n + 1>>.
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RETURNS
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This function returns the initial value of <[dst]>
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PORTABILITY
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<<strncat>> is ANSI C.
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<<strncat>> requires no supporting OS subroutines.
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QUICKREF
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strncat ansi pure
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*/
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#include <string.h>
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#include <limits.h>
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/* Nonzero if X is aligned on a "long" boundary. */
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#define ALIGNED(X) \
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(((long)X & (sizeof (long) - 1)) == 0)
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#if LONG_MAX == 2147483647L
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#define DETECTNULL(X) (((X) - 0x01010101) & ~(X) & 0x80808080)
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#else
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#if LONG_MAX == 9223372036854775807L
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/* Nonzero if X (a long int) contains a NULL byte. */
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#define DETECTNULL(X) (((X) - 0x0101010101010101) & ~(X) & 0x8080808080808080)
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#else
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#error long int is not a 32bit or 64bit type.
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#endif
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#endif
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#ifndef DETECTNULL
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#error long int is not a 32bit or 64bit byte
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#endif
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char *
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_DEFUN (strncat, (s1, s2, n),
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char *__restrict s1 _AND
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_CONST char *__restrict s2 _AND
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size_t n)
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{
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#if defined(PREFER_SIZE_OVER_SPEED) || defined(__OPTIMIZE_SIZE__)
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char *s = s1;
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while (*s1)
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s1++;
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while (n-- != 0 && (*s1++ = *s2++))
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{
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if (n == 0)
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*s1 = '\0';
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}
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return s;
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#else
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char *s = s1;
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/* Skip over the data in s1 as quickly as possible. */
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if (ALIGNED (s1))
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{
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unsigned long *aligned_s1 = (unsigned long *)s1;
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while (!DETECTNULL (*aligned_s1))
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aligned_s1++;
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s1 = (char *)aligned_s1;
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}
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while (*s1)
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s1++;
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/* s1 now points to the its trailing null character, now copy
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up to N bytes from S2 into S1 stopping if a NULL is encountered
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in S2.
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It is not safe to use strncpy here since it copies EXACTLY N
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characters, NULL padding if necessary. */
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while (n-- != 0 && (*s1++ = *s2++))
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{
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if (n == 0)
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*s1 = '\0';
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}
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return s;
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#endif /* not PREFER_SIZE_OVER_SPEED */
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}
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