--- a/ChangeLog
+++ b/ChangeLog
@@ -1,3 +1,11 @@
+2009-10-18  Bruno Haible  <bruno@clisp.org>
+
+	New module 'isblank'.
+	* lib/isblank.c: New file.
+	* m4/isblank.m4: New file.
+	* modules/isblank: New file.
+	* doc/posix-functions/isblank.texi: Mention the new module.
+
 2009-10-18  Bruno Haible  <bruno@clisp.org>
 
 	New module 'ctype'.

--- a/doc/posix-functions/isblank.texi
+++ b/doc/posix-functions/isblank.texi
@@ -4,15 +4,15 @@
 
 POSIX specification: @url{http://www.opengroup.org/onlinepubs/9699919799/functions/isblank.html}
 
-Gnulib module: ---
+Gnulib module: isblank
 
 Portability problems fixed by Gnulib:
 @itemize
-@end itemize
-
-Portability problems not fixed by Gnulib:
-@itemize
 @item
 This function is missing on some platforms:
 AIX 4.3.2, IRIX 6.5, OSF/1 5.1, Solaris 9, mingw.
 @end itemize
+
+Portability problems not fixed by Gnulib:
+@itemize
+@end itemize

new file mode 100644
--- /dev/null
+++ b/lib/isblank.c
@@ -0,0 +1,33 @@
+/* Test whether a character is a blank.
+
+   Copyright (C) 2009 Free Software Foundation, Inc.
+
+   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 <ctype.h>
+
+int
+isblank (int c)
+{
+  /* On all known platforms, in all predefined locales, isblank(c) is likely
+     equivalent with  (c == ' ' || c == '\t').  Look at the glibc definition
+     (in glibc/localedata/locales/i18n): The "blank" characters are '\t', ' ',
+     U+1680, U+180E, U+2000..U+2006, U+2008..U+200A, U+205F, U+3000, and none
+     except the first two is present in a common 8-bit encoding.  Therefore
+     the substitute for other platforms is not more complicated than this.  */
+  return (c == ' ' || c == '\t');
+}

new file mode 100644
--- /dev/null
+++ b/m4/isblank.m4
@@ -0,0 +1,19 @@
+# isblank.m4 serial 1
+dnl Copyright (C) 2009 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_ISBLANK],
+[
+  dnl Persuade glibc <ctype.h> to declare isblank().
+  AC_REQUIRE([AC_USE_SYSTEM_EXTENSIONS])
+
+  AC_REQUIRE([gl_CTYPE_H_DEFAULTS])
+  AC_CHECK_FUNCS_ONCE([isblank])
+  if test $ac_cv_func_isblank = no; then
+    HAVE_ISBLANK=0
+    CTYPE_H='ctype.h'
+    AC_LIBOBJ([isblank])
+  fi
+])

new file mode 100644
--- /dev/null
+++ b/modules/isblank
@@ -0,0 +1,25 @@
+Description:
+isblank() function: test whether a single-byte character is a blank.
+
+Files:
+lib/isblank.c
+m4/isblank.m4
+
+Depends-on:
+extensions
+ctype
+
+configure.ac:
+gl_FUNC_ISBLANK
+gl_CTYPE_MODULE_INDICATOR([isblank])
+
+Makefile.am:
+
+Include:
+<ctype.h>
+
+License:
+LGPLv2+
+
+Maintainer:
+Bruno Haible