--- a/ChangeLog
+++ b/ChangeLog
@@ -1,3 +1,18 @@
+2008-12-18  Bruno Haible  <bruno@clisp.org>
+
+	New module 'mbrtowc'.
+	* lib/wchar.in.h (mbstate_t): Override when the system does not have
+	mbsinit and mbrtowc.
+	(mbrtowc): New declaration.
+	* lib/mbrtowc.c: New file.
+	* m4/mbrtowc.m4 (gl_FUNC_MBRTOWC, gl_PREREQ_MBRTOWC): New macros.
+	* modules/mbrtowc: New file.
+	* m4/wchar.m4 (gl_WCHAR_H_DEFAULTS): Initialize GNULIB_MBRTOWC and
+	HAVE_MBRTOWC.
+	* modules/wchar (Makefile.am): Substitute GNULIB_MBRTOWC and
+	HAVE_MBRTOWC.
+	* doc/posix-functions/mbrtowc.texi: Document the new module.
+
 2008-12-18  Bruno Haible  <bruno@clisp.org>
 
 	New module 'wctob'.

--- a/doc/posix-functions/mbrtowc.texi
+++ b/doc/posix-functions/mbrtowc.texi
@@ -4,18 +4,18 @@
 
 POSIX specification: @url{http://www.opengroup.org/onlinepubs/9699919799/functions/mbrtowc.html}
 
-Gnulib module: ---
+Gnulib module: mbrtowc
 
 Portability problems fixed by Gnulib:
 @itemize
+@item
+This function is missing on some platforms:
+HP-UX 11, IRIX 6.5, Solaris 2.6, mingw, Interix 3.5.
 @end itemize
 
 Portability problems not fixed by Gnulib:
 @itemize
 @item
-This function is missing on some platforms:
-HP-UX 11, IRIX 6.5, Solaris 2.6, mingw, Interix 3.5.
-@item
 On Windows platforms, @code{wchar_t} is a 16-bit type and therefore cannot
 accommodate all Unicode characters.
 @end itemize

new file mode 100644
--- /dev/null
+++ b/lib/mbrtowc.c
@@ -0,0 +1,271 @@
+/* Convert multibyte character to wide character.
+   Copyright (C) 1999-2002, 2005-2008 Free Software Foundation, Inc.
+   Written by Bruno Haible <bruno@clisp.org>, 2008.
+
+   This program is free software: you can redistribute it and/or modify
+   it under the terms of the GNU General Public License as published by
+   the Free Software Foundation; either version 3 of the License, or
+   (at your option) any later version.
+
+   This program 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 General Public License for more details.
+
+   You should have received a copy of the GNU General Public License
+   along with this program.  If not, see <http://www.gnu.org/licenses/>.  */
+
+#include <config.h>
+
+/* Specification.  */
+#include <wchar.h>
+
+#include <errno.h>
+#include <stdlib.h>
+
+#include "localcharset.h"
+#include "streq.h"
+
+
+static char internal_state[4];
+
+size_t
+mbrtowc (wchar_t *pwc, const char *s, size_t n, mbstate_t *ps)
+{
+  char *pstate = (char *)ps;
+
+  if (pstate == NULL)
+    pstate = internal_state;
+
+  if (s == NULL)
+    {
+      pwc = NULL;
+      s = "";
+      n = 1;
+    }
+
+  if (n == 0)
+    return (size_t)(-2);
+
+  /* Here n > 0.  */
+  {
+    size_t nstate = pstate[0];
+    char buf[4];
+    const char *p;
+    size_t m;
+
+    switch (nstate)
+      {
+      case 0:
+	p = s;
+	m = n;
+	break;
+      case 3:
+	buf[2] = pstate[3];
+	/*FALLTHROUGH*/
+      case 2:
+	buf[1] = pstate[2];
+	/*FALLTHROUGH*/
+      case 1:
+	buf[0] = pstate[1];
+	p = buf;
+	m = nstate;
+	buf[m++] = s[0];
+	if (n >= 2 && m < 4)
+	  {
+	    buf[m++] = s[1];
+	    if (n >= 3 && m < 4)
+	      buf[m++] = s[2];
+	  }
+	break;
+      default:
+	errno = EINVAL;
+	return (size_t)(-1);
+      }
+
+    /* Here 0 < m ≤ 4.  */
+
+#if __GLIBC__
+    /* Work around bug <http://sourceware.org/bugzilla/show_bug.cgi?id=9674> */
+    mbtowc (NULL, NULL, 0);
+#endif
+    {
+      int res = mbtowc (pwc, p, m);
+
+      if (res >= 0)
+	{
+	  if (pwc != NULL && ((*pwc == 0) != (res == 0)))
+	    abort ();
+	  if (nstate >= (res > 0 ? res : 1))
+	    abort ();
+	  res -= nstate;
+	  pstate[0] = 0;
+	  return res;
+	}
+
+      /* mbtowc does not distinguish between invalid and incomplete multibyte
+	 sequences.  But mbrtowc needs to make this distinction.
+	 There are two possible approaches:
+	   - Use iconv() and its return value.
+	   - Use built-in knowledge about the possible encodings.
+	 Given the low quality of implementation of iconv() on the systems that
+	 lack mbrtowc(), we use the second approach.
+	 The possible encodings are:
+	   - 8-bit encodings,
+	   - EUC-JP, EUC-KR, GB2312, EUC-TW, BIG5, SJIS,
+	   - UTF-8.
+	 Use specialized code for each.  */
+      if (m >= 4 || m >= MB_CUR_MAX)
+	goto invalid;
+      /* Here MB_CUR_MAX > 1 and 0 < m < 4.  */
+      {
+	const char *encoding = locale_charset ();
+
+	if (STREQ (encoding, "UTF-8", 'U', 'T', 'F', '-', '8', 0, 0, 0, 0))
+	  {
+	    /* Cf. unistr/u8-mblen.c.  */
+	    unsigned char c = (unsigned char) p[0];
+
+	    if (c >= 0xc2)
+	      {
+		if (c < 0xe0)
+		  {
+		    if (m == 1)
+		      goto incomplete;
+		  }
+		else if (c < 0xf0)
+		  {
+		    if (m == 1)
+		      goto incomplete;
+		    if (m == 2)
+		      {
+			unsigned char c2 = (unsigned char) p[1];
+
+			if ((c2 ^ 0x80) < 0x40
+			    && (c >= 0xe1 || c2 >= 0xa0)
+			    && (c != 0xed || c2 < 0xa0))
+			  goto incomplete;
+		      }
+		  }
+		else if (c <= 0xf4)
+		  {
+		    if (m == 1)
+		      goto incomplete;
+		    else /* m == 2 || m == 3 */
+		      {
+			unsigned char c2 = (unsigned char) p[1];
+
+			if ((c2 ^ 0x80) < 0x40
+			    && (c >= 0xf1 || c2 >= 0x90)
+			    && (c < 0xf4 || (c == 0xf4 && c2 < 0x90)))
+			  {
+			    if (m == 2)
+			      goto incomplete;
+			    else /* m == 3 */
+			      {
+				unsigned char c3 = (unsigned char) p[2];
+
+				if ((c3 ^ 0x80) < 0x40)
+				  goto incomplete;
+			      }
+			  }
+		      }
+		  }
+	      }
+	    goto invalid;
+	  }
+
+	/* As a reference for this code, you can use the GNU libiconv
+	   implementation.  Look for uses of the RET_TOOFEW macro.  */
+
+	if (STREQ (encoding, "EUC-JP", 'E', 'U', 'C', '-', 'J', 'P', 0, 0, 0))
+	  {
+	    if (m == 1)
+	      {
+		unsigned char c = (unsigned char) p[0];
+
+		if ((c >= 0xa1 && c < 0xff) || c == 0x8e || c == 0x8f)
+		  goto incomplete;
+	      }
+	    if (m == 2)
+	      {
+		unsigned char c = (unsigned char) p[0];
+
+		if (c == 0x8f)
+		  {
+		    unsigned char c2 = (unsigned char) p[1];
+
+		    if (c2 >= 0xa1 && c2 < 0xff)
+		      goto incomplete;
+		  }
+	      }
+	    goto invalid;
+	  }
+	if (STREQ (encoding, "EUC-KR", 'E', 'U', 'C', '-', 'K', 'R', 0, 0, 0)
+	    || STREQ (encoding, "GB2312", 'G', 'B', '2', '3', '1', '2', 0, 0, 0)
+	    || STREQ (encoding, "BIG5", 'B', 'I', 'G', '5', 0, 0, 0, 0, 0))
+	  {
+	    if (m == 1)
+	      {
+		unsigned char c = (unsigned char) p[0];
+
+		if (c >= 0xa1 && c < 0xff)
+		  goto incomplete;
+	      }
+	    goto invalid;
+	  }
+	if (STREQ (encoding, "EUC-TW", 'E', 'U', 'C', '-', 'T', 'W', 0, 0, 0))
+	  {
+	    if (m == 1)
+	      {
+		unsigned char c = (unsigned char) p[0];
+
+		if ((c >= 0xa1 && c < 0xff) || c == 0x8e)
+		  goto incomplete;
+	      }
+	    else /* m == 2 || m == 3 */
+	      {
+		unsigned char c = (unsigned char) p[0];
+
+		if (c == 0x8e)
+		  goto incomplete;
+	      }
+	    goto invalid;
+	  }
+	if (STREQ (encoding, "SJIS", 'S', 'J', 'I', 'S', 0, 0, 0, 0, 0))
+	  {
+	    if (m == 1)
+	      {
+		unsigned char c = (unsigned char) p[0];
+
+		if ((c >= 0x81 && c <= 0x9f) || (c >= 0xe0 && c <= 0xea)
+		    || (c >= 0xf0 && c <= 0xf9))
+		  goto incomplete;
+	      }
+	    goto invalid;
+	  }
+
+	/* An unknown multibyte encoding.  */
+	goto incomplete;
+      }
+
+     incomplete:
+      {
+	size_t k = nstate;
+	/* Here 0 < k < m < 4.  */
+	pstate[++k] = s[0];
+	if (k < m)
+	  pstate[++k] = s[1];
+	if (k != m)
+	  abort ();
+      }
+      pstate[0] = m;
+      return (size_t)(-2);
+
+     invalid:
+      errno = EILSEQ;
+      /* The conversion state is undefined, says POSIX.  */
+      return (size_t)(-1);
+    }
+  }
+}

--- a/lib/wchar.in.h
+++ b/lib/wchar.in.h
@@ -71,6 +71,16 @@
 #endif
 
 
+/* Override mbstate_t if it is too small.
+   On IRIX 6.5, sizeof (mbstate_t) == 1, which is not sufficient for
+   implementing mbrtowc for encodings like UTF-8.  */
+#if !(@HAVE_MBSINIT@ && @HAVE_MBRTOWC@)
+typedef int rpl_mbstate_t;
+# undef mbstate_t
+# define mbstate_t rpl_mbstate_t
+#endif
+
+
 /* Convert a single-byte character to a wide character.  */
 #if @GNULIB_BTOWC@
 # if !@HAVE_BTOWC@
@@ -113,6 +123,20 @@
 #endif
 
 
+/* Convert a multibyte character to a wide character.  */
+#if @GNULIB_MBRTOWC@
+# if !@HAVE_MBRTOWC@
+extern size_t mbrtowc (wchar_t *pwc, const char *s, size_t n, mbstate_t *ps);
+# endif
+#elif defined GNULIB_POSIXCHECK
+# undef mbrtowc
+# define mbrtowc(w,s,n,p) \
+    (GL_LINK_WARNING ("mbrtowc is unportable - " \
+                      "use gnulib module mbrtowc for portability"), \
+     mbrtowc (w, s, n, p))
+#endif
+
+
 /* Return the number of screen columns needed for WC.  */
 #if @GNULIB_WCWIDTH@
 # if @REPLACE_WCWIDTH@

--- a/m4/mbrtowc.m4
+++ b/m4/mbrtowc.m4
@@ -1,9 +1,29 @@
-# mbrtowc.m4 serial 9
+# mbrtowc.m4 serial 10
 dnl Copyright (C) 2001-2002, 2004-2005, 2008 Free Software Foundation, Inc.
 dnl This file is free software; the Free Software Foundation
 dnl gives unlimited permission to copy and/or distribute it,
 dnl with or without modifications, as long as this notice is preserved.
 
+AC_DEFUN([gl_FUNC_MBRTOWC],
+[
+  AC_REQUIRE([gl_WCHAR_H_DEFAULTS])
+
+  AC_REQUIRE([AC_TYPE_MBSTATE_T])
+  AC_CHECK_FUNCS_ONCE([mbrtowc])
+  if test $ac_cv_func_mbrtowc = no; then
+    HAVE_MBRTOWC=0
+    gl_REPLACE_WCHAR_H
+    AC_LIBOBJ([mbrtowc])
+    gl_PREREQ_MBRTOWC
+  fi
+])
+
+# Prerequisites of lib/mbrtowc.c.
+AC_DEFUN([gl_PREREQ_MBRTOWC], [
+  :
+])
+
+
 dnl From Paul Eggert
 
 dnl This override of an autoconf macro can be removed when autoconf 2.60 or

--- a/m4/wchar.m4
+++ b/m4/wchar.m4
@@ -64,11 +64,13 @@
   GNULIB_BTOWC=0;   AC_SUBST([GNULIB_BTOWC])
   GNULIB_WCTOB=0;   AC_SUBST([GNULIB_WCTOB])
   GNULIB_MBSINIT=0; AC_SUBST([GNULIB_MBSINIT])
+  GNULIB_MBRTOWC=0; AC_SUBST([GNULIB_MBRTOWC])
   GNULIB_WCWIDTH=0; AC_SUBST([GNULIB_WCWIDTH])
   dnl Assume proper GNU behavior unless another module says otherwise.
   HAVE_BTOWC=1;        AC_SUBST([HAVE_BTOWC])
   HAVE_WCTOB=1;        AC_SUBST([HAVE_WCTOB])
   HAVE_MBSINIT=1;      AC_SUBST([HAVE_MBSINIT])
+  HAVE_MBRTOWC=1;      AC_SUBST([HAVE_MBRTOWC])
   HAVE_DECL_WCWIDTH=1; AC_SUBST([HAVE_DECL_WCWIDTH])
   REPLACE_WCWIDTH=0;   AC_SUBST([REPLACE_WCWIDTH])
   WCHAR_H='';          AC_SUBST([WCHAR_H])

new file mode 100644
--- /dev/null
+++ b/modules/mbrtowc
@@ -0,0 +1,28 @@
+Description:
+mbrtowc() function: convert multibyte character to wide character.
+
+Files:
+lib/mbrtowc.c
+m4/mbrtowc.m4
+m4/mbstate_t.m4
+
+Depends-on:
+wchar
+localcharset
+streq
+
+configure.ac:
+gl_FUNC_MBRTOWC
+gl_WCHAR_MODULE_INDICATOR([mbrtowc])
+
+Makefile.am:
+
+Include:
+<wchar.h>
+
+License:
+LGPL
+
+Maintainer:
+Bruno Haible
+

--- a/modules/wchar
+++ b/modules/wchar
@@ -28,11 +28,13 @@
 	      -e 's|@''GNULIB_BTOWC''@|$(GNULIB_BTOWC)|g' \
 	      -e 's|@''GNULIB_WCTOB''@|$(GNULIB_WCTOB)|g' \
 	      -e 's|@''GNULIB_MBSINIT''@|$(GNULIB_MBSINIT)|g' \
+	      -e 's|@''GNULIB_MBRTOWC''@|$(GNULIB_MBRTOWC)|g' \
 	      -e 's|@''GNULIB_WCWIDTH''@|$(GNULIB_WCWIDTH)|g' \
 	      -e 's|@''HAVE_WINT_T''@|$(HAVE_WINT_T)|g' \
 	      -e 's|@''HAVE_BTOWC''@|$(HAVE_BTOWC)|g' \
 	      -e 's|@''HAVE_WCTOB''@|$(HAVE_WCTOB)|g' \
 	      -e 's|@''HAVE_MBSINIT''@|$(HAVE_MBSINIT)|g' \
+	      -e 's|@''HAVE_MBRTOWC''@|$(HAVE_MBRTOWC)|g' \
 	      -e 's|@''HAVE_DECL_WCWIDTH''@|$(HAVE_DECL_WCWIDTH)|g' \
 	      -e 's|@''REPLACE_WCWIDTH''@|$(REPLACE_WCWIDTH)|g' \
 	      -e '/definition of GL_LINK_WARNING/r $(LINK_WARNING_H)' \