source: trunk/libs/newlib/src/newlib/libc/string/stpncpy.c @ 577

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

INDEX
        stpncpy

SYNOPSIS
        #include <string.h>
        char *stpncpy(char *restrict <[dst]>, const char *restrict <[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 *
stpncpy (char *__restrict dst,
        const char *__restrict src,
        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;
}