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