Add the wcslcpy, wcslcat functions

These functions are about to be added to POSIX, under Austin Group
issue 986.

Reviewed-by: Siddhesh Poyarekar <siddhesh@sourceware.org>

wcsmbs/wcslcpy.c

@@ -0,0 +1,46 @@
+/* Copy a null-terminated wide string to a fixed-size buffer.
+   Copyright (C) 2023 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 <wchar.h>
+
+size_t
+__wcslcpy (wchar_t *__restrict dest, const wchar_t *__restrict src, size_t size)
+{
+  size_t src_length = __wcslen (src);
+
+  if (__glibc_unlikely (src_length >= size))
+    {
+      if (size > 0)
+	{
+	  /* Copy the leading portion of the string.  The last
+	     character is subsequently overwritten with the null
+	     terminator, but the destination size is usually a
+	     multiple of a small power of two, so writing it twice
+	     should be more efficient than copying an odd number of
+	     character.  */
+	  __wmemcpy (dest, src, size);
+	  dest[size - 1] = '\0';
+	}
+    }
+  else
+    /* Copy the string and its terminating null character.  */
+    __wmemcpy (dest, src, src_length + 1);
+  return src_length;
+}
+libc_hidden_def (__wcslcpy)
+weak_alias (__wcslcpy, wcslcpy)