c32tolower: New module.

* lib/uchar.in.h (c32tolower): New declaration.
* lib/c32tolower.c: New file.
* lib/c32to-impl.h: New file, based on lib/c32is-impl.h.
* modules/c32tolower: New file.
* m4/uchar_h.m4 (gl_UCHAR_H_REQUIRE_DEFAULTS): Initialize
GNULIB_C32TOLOWER.
* modules/uchar (Makefile.am): Substitute GNULIB_C32TOLOWER.

1 files changed, 92 insertions, 0 deletions

diff --git a/lib/c32to-impl.h b/lib/c32to-impl.h
new file mode 100644
index 0000000000..724691a116
--- /dev/null
+++ b/lib/c32to-impl.h
@@ -0,0 +1,92 @@
+/* Case mapping of a 32-bit wide character.
+   Copyright (C) 2020-2023 Free Software Foundation, Inc.
+
+   This file is free software.
+   It is dual-licensed under "the GNU LGPLv3+ or the GNU GPLv2+".
+   You can redistribute it and/or modify it under either
+     - the terms of the GNU Lesser General Public License as published
+       by the Free Software Foundation, either version 3, or (at your
+       option) any later version, or
+     - the terms of the GNU General Public License as published by the
+       Free Software Foundation; either version 2, or (at your option)
+       any later version, or
+     - the same dual license "the GNU LGPLv3+ or the GNU GPLv2+".
+
+   This file 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 and the GNU General Public License
+   for more details.
+
+   You should have received a copy of the GNU Lesser General Public
+   License and of the GNU General Public License along with this
+   program.  If not, see <https://www.gnu.org/licenses/>.  */
+
+/* Written by Bruno Haible <bruno@clisp.org>, 2023.  */
+
+#include <wchar.h>
+#include <wctype.h>
+
+#if GNULIB_defined_mbstate_t
+# include "localcharset.h"
+# include "streq.h"
+#endif
+
+#include "unicase.h"
+
+#if _GL_WCHAR_T_IS_UCS4 && !GNULIB_defined_mbstate_t
+_GL_EXTERN_INLINE
+#endif
+wint_t
+FUNC (wint_t wc)
+{
+  /* The char32_t encoding of a multibyte character is defined by the way
+     mbrtoc32() is defined.  */
+
+#if GNULIB_defined_mbstate_t            /* AIX, IRIX */
+  /* mbrtoc32() is defined on top of mbtowc() for the non-UTF-8 locales
+     and directly for the UTF-8 locales.  */
+  if (wc != WEOF)
+    {
+      const char *encoding = locale_charset ();
+      if (STREQ_OPT (encoding, "UTF-8", 'U', 'T', 'F', '-', '8', 0, 0, 0, 0))
+        return UCS_FUNC (wc);
+      else
+        return WCHAR_FUNC (wc);
+    }
+  else
+    return wc;
+
+#elif HAVE_WORKING_MBRTOC32             /* glibc */
+  /* mbrtoc32() is essentially defined by the system libc.  */
+
+# if _GL_WCHAR_T_IS_UCS4
+  /* The char32_t encoding of a multibyte character is known to be the same as
+     the wchar_t encoding.  */
+  return WCHAR_FUNC (wc);
+# else
+  /* The char32_t encoding of a multibyte character is known to be UCS-4,
+     different from the wchar_t encoding.  */
+  if (wc != WEOF)
+    return UCS_FUNC (wc);
+  else
+    return wc;
+# endif
+
+#elif _GL_SMALL_WCHAR_T                 /* Cygwin, mingw, MSVC */
+  /* The wchar_t encoding is UTF-16.
+     The char32_t encoding is UCS-4.  */
+
+  if (wc == WEOF || wc == (wchar_t) wc)
+    /* wc is in the range for the tow* functions.  */
+    return WCHAR_FUNC (wc);
+  else
+    return UCS_FUNC (wc);
+
+#else /* macOS, FreeBSD, NetBSD, OpenBSD, HP-UX, Solaris, Minix, Android */
+  /* char32_t and wchar_t are equivalent.  */
+  static_assert (sizeof (char32_t) == sizeof (wchar_t));
+
+  return WCHAR_FUNC (wc);
+#endif
+}