1  /* Append a null-terminated wide string to another, with length checking.
       2     Copyright (C) 2023 Free Software Foundation, Inc.
       3     This file is part of the GNU C Library.
       4  
       5     The GNU C Library is free software; you can redistribute it and/or
       6     modify it under the terms of the GNU Lesser General Public
       7     License as published by the Free Software Foundation; either
       8     version 2.1 of the License, or (at your option) any later version.
       9  
      10     The GNU C Library is distributed in the hope that it will be useful,
      11     but WITHOUT ANY WARRANTY; without even the implied warranty of
      12     MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
      13     Lesser General Public License for more details.
      14  
      15     You should have received a copy of the GNU Lesser General Public
      16     License along with the GNU C Library; if not, see
      17     <https://www.gnu.org/licenses/>.  */
      18  
      19  #include <stdint.h>
      20  #include <wchar.h>
      21  
      22  size_t
      23  __wcslcat (wchar_t *__restrict dest, const wchar_t *__restrict src,
      24             size_t size)
      25  {
      26    size_t src_length = __wcslen (src);
      27  
      28    /* Our implementation strlcat supports dest == NULL if size == 0
      29       (for consistency with snprintf and strlcpy), but wcsnlen does
      30       not, so we have to cover this case explicitly.  */
      31    if (size == 0)
      32      return src_length;
      33  
      34    size_t dest_length = __wcsnlen (dest, size);
      35    if (dest_length != size)
      36      {
      37        /* Copy at most the remaining number of characters in the
      38  	 destination buffer.  Leave for the null terminator.  */
      39        size_t to_copy = size - dest_length - 1;
      40        /* But not more than what is available in the source string.  */
      41        if (to_copy > src_length)
      42  	to_copy = src_length;
      43  
      44        wchar_t *target = dest + dest_length;
      45        __wmemcpy (target, src, to_copy);
      46        target[to_copy] = '\0';
      47      }
      48  
      49    /* If the sum wraps around, we have more than SIZE_MAX + 2 bytes in
      50       the two input strings (including both null terminators).  If each
      51       byte in the address space can be assigned a unique size_t value
      52       (which the static_assert checks), then by the pigeonhole
      53       principle, the two input strings must overlap, which is
      54       undefined.  */
      55    _Static_assert (sizeof (uintptr_t) == sizeof (size_t),
      56  		  "theoretical maximum object size covers address space");
      57    return dest_length + src_length;
      58  }
      59  libc_hidden_def (__wcslcat)
      60  weak_alias (__wcslcat, wcslcat)