strncpy.c

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/*
FUNCTION
	<<strncpy>>---counted copy string

INDEX
	strncpy

ANSI_SYNOPSIS
	#include <string.h>
	char *strncpy(char *<[dst]>, const char *<[src]>, size_t <[length]>);

TRAD_SYNOPSIS
	#include <string.h>
	char *strncpy(<[dst]>, <[src]>, <[length]>)
	char *<[dst]>;
	char *<[src]>;
	size_t <[length]>;

DESCRIPTION
	<<strncpy>> 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 the initial value of <[dst]>.

PORTABILITY
<<strncpy>> is ANSI C.

<<strncpy>> requires no supporting OS subroutines.

QUICKREF
	strncpy ansi pure
*/

#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 (strncpy, (dst0, src0),
	char *dst0 _AND
	_CONST char *src0 _AND
	size_t count)
{
#if defined(PREFER_SIZE_OVER_SPEED) || defined(__OPTIMIZE_SIZE__)
  char *dscan;
  _CONST char *sscan;

  dscan = dst0;
  sscan = src0;
  while (count > 0)
    {
      --count;
      if ((*dscan++ = *sscan++) == '\0')
	break;
    }
  while (count-- > 0)
    *dscan++ = '\0';

  return dst0;
#else
  char *dst = dst0;
  _CONST char *src = src0;
  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;
    }

  while (count > 0)
    {
      --count;
      if ((*dst++ = *src++) == '\0')
	break;
    }

  while (count-- > 0)
    *dst++ = '\0';

  return dst0;
#endif /* not PREFER_SIZE_OVER_SPEED */
}