stpncpy.c

来自「Newlib 嵌入式 C库 标准实现代码」· C语言 代码 · 共 115 行

/*
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;
}