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/*

FUNCTION

        <<stpncpy>>---counted copy string returning a pointer to its end

INDEX

        stpncpy

ANSI_SYNOPSIS

        #include <string.h>

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

TRAD_SYNOPSIS

        #include <string.h>

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

        char *<[dst]>;

        char *<[src]>;

        size_t <[length]>;

DESCRIPTION

        <<stpncpy>> copies not more than <[length]> characters from the

        the string pointed to by <[src]> (including the terminating

        null character) to the array pointed to by <[dst]>.  If the

        string pointed to by <[src]> is shorter than <[length]>

        characters, null characters are appended to the destination

        array until a total of <[length]> characters have been

        written.

RETURNS

        This function returns a pointer to the end of the destination string,

        thus pointing to the trailing '\0', or, if the destination string is

        not null-terminated, pointing to dst + n.

PORTABILITY

<<stpncpy>> is a GNU extension, candidate for inclusion into POSIX/SUSv4.

<<stpncpy>> requires no supporting OS subroutines.

QUICKREF

        stpncpy gnu

*/

#include <string.h>

#include <limits.h>

/*SUPPRESS 560*/

/*SUPPRESS 530*/

/* Nonzero if either X or Y is not aligned on a "long" boundary.  */

#define UNALIGNED(X, Y) \

  (((long)X & (sizeof (long) - 1)) | ((long)Y & (sizeof (long) - 1)))

#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

#define TOO_SMALL(LEN) ((LEN) < sizeof (long))

char *

_DEFUN (stpncpy, (dst, src),

        char *dst _AND

        _CONST char *src _AND

        size_t count)

{

  char *ret = NULL;

#if !defined(PREFER_SIZE_OVER_SPEED) && !defined(__OPTIMIZE_SIZE__)

  long *aligned_dst;

  _CONST long *aligned_src;

  /* If SRC and DEST is aligned and count large enough, then copy words.  */

  if (!UNALIGNED (src, dst) && !TOO_SMALL (count))

    {

      aligned_dst = (long*)dst;

      aligned_src = (long*)src;

      /* SRC and DEST are both "long int" aligned, try to do "long int"

         sized copies.  */

      while (count >= sizeof (long int) && !DETECTNULL(*aligned_src))

        {

          count -= sizeof (long int);

          *aligned_dst++ = *aligned_src++;

        }

      dst = (char*)aligned_dst;

      src = (char*)aligned_src;

    }

#endif /* not PREFER_SIZE_OVER_SPEED */

  while (count > 0)

    {

      --count;

      if ((*dst++ = *src++) == '\0')

        {

          ret = dst - 1;

          break;

        }

    }

  while (count-- > 0)

    *dst++ = '\0';

  return ret ? ret : dst;

}