glibc/sysdeps/generic/strncpy.c

/* Copyright (C) 1991, 1997 Free Software Foundation, Inc.
   This file is part of the GNU C Library.

   The GNU C Library is free software; you can redistribute it and/or
   modify it under the terms of the GNU Library General Public License as
   published by the Free Software Foundation; either version 2 of the
   License, or (at your option) any later version.

   The GNU C Library is distributed in the hope that it will be useful,
   but WITHOUT ANY WARRANTY; without even the implied warranty of
   MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
   Library General Public License for more details.

   You should have received a copy of the GNU Library General Public
   License along with the GNU C Library; see the file COPYING.LIB.  If not,
   write to the Free Software Foundation, Inc., 59 Temple Place - Suite 330,
   Boston, MA 02111-1307, USA.  */

#include <string.h>
#include <memcopy.h>

#undef strncpy

char *
strncpy (s1, s2, n)
     char *s1;
     const char *s2;
     size_t n;
{
  reg_char c;
  char *s = s1;

  --s1;

  if (n >= 4)
    {
      size_t n4 = n >> 2;

      for (;;)
	{
	  c = *s2++;
	  *++s1 = c;
	  if (c == '\0')
	    break;
	  c = *s2++;
	  *++s1 = c;
	  if (c == '\0')
	    break;
	  c = *s2++;
	  *++s1 = c;
	  if (c == '\0')
	    break;
	  c = *s2++;
	  *++s1 = c;
	  if (c == '\0')
	    break;
	  if (--n4 == 0)
	    goto last_chars;
	}
      n = n - (s1 - s) - 1;
      if (n == 0)
	return s;
      goto zero_fill;
    }

 last_chars:
  n &= 3;
  if (n == 0)
    return s;

  do
    {
      c = *s2++;
      *++s1 = c;
      if (--n == 0)
	return s;
    }
  while (c != '\0');

 zero_fill:
  do
    *++s1 = '\0';
  while (--n > 0);

  return s;
}