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/*

FUNCTION

        <<strncat>>---concatenate strings

INDEX

        strncat

ANSI_SYNOPSIS

        #include <string.h>

        char *strncat(char *<[dst]>, const char *<[src]>, size_t <[length]>);

TRAD_SYNOPSIS

        #include <string.h>

        char *strncat(<[dst]>, <[src]>, <[length]>)

        char *<[dst]>;

        char *<[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 *s1 _AND

        _CONST char *s2 _AND

        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 */

}