/* Copyright (C) 1991-2018 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 Lesser General Public

   License as published by the Free Software Foundation; either

   version 2.1 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

   Lesser General Public License for more details.

   You should have received a copy of the GNU Lesser General Public

   License along with the GNU C Library; if not, see

   <http://www.gnu.org/licenses/>.  */

#include <string.h>

#include <memcopy.h>

char *

__strncat_chk (char *s1, const char *s2, size_t n, size_t s1len)

{

  char c;

  char *s = s1;

  /* Find the end of S1.  */

  do

    {

      if (__glibc_unlikely (s1len-- == 0))

	__chk_fail ();

      c = *s1++;

    }

  while (c != '\0');

  /* Make S1 point before next character, so we can increment

     it while memory is read (wins on pipelined cpus).  */

  ++s1len;

  s1 -= 2;

  if (n >= 4)

    {

      size_t n4 = n >> 2;

      do

	{

	  if (__glibc_unlikely (s1len-- == 0))

	    __chk_fail ();

	  c = *s2++;

	  *++s1 = c;

	  if (c == '\0')

	    return s;

	  if (__glibc_unlikely (s1len-- == 0))

	    __chk_fail ();

	  c = *s2++;

	  *++s1 = c;

	  if (c == '\0')

	    return s;

	  if (__glibc_unlikely (s1len-- == 0))

	    __chk_fail ();

	  c = *s2++;

	  *++s1 = c;

	  if (c == '\0')

	    return s;

	  if (__glibc_unlikely (s1len-- == 0))

	    __chk_fail ();

	  c = *s2++;

	  *++s1 = c;

	  if (c == '\0')

	    return s;

	} while (--n4 > 0);

      n &= 3;

    }

  while (n > 0)

    {

      if (__glibc_unlikely (s1len-- == 0))

	__chk_fail ();

      c = *s2++;

      *++s1 = c;

      if (c == '\0')

	return s;

      n--;

    }

  if (c != '\0')

    {

      if (__glibc_unlikely (s1len-- == 0))

	__chk_fail ();

      *++s1 = '\0';

    }

  return s;

}