--- a/ChangeLog
+++ b/ChangeLog
@@ -1,3 +1,9 @@
+2005-08-17  Bruno Haible  <bruno@clisp.org>
+
+	* modules/strcasestr: New file.
+	* MODULES.html.sh (String handling, based on ANSI C 89): Add
+	strcasestr.
+
 2005-08-17  Bruno Haible  <bruno@clisp.org>
 
 	* modules/strstr (Files): Add m4/mbrtowc.m4.

--- a/MODULES.html.sh
+++ b/MODULES.html.sh
@@ -1517,6 +1517,7 @@
   func_module stpcpy
   func_module stpncpy
   func_module strcase
+  func_module strcasestr
   func_module strchrnul
   func_module strdup
   func_module strnlen

--- a/lib/ChangeLog
+++ b/lib/ChangeLog
@@ -1,3 +1,8 @@
+2005-08-17  Bruno Haible  <bruno@clisp.org>
+
+	* strcasestr.h: New file.
+	* strcasestr.c: New file.
+
 2005-08-17  Bruno Haible  <bruno@clisp.org>
 
 	* strstr.h: Ignore HAVE_STRSTR, always declare the gnulib function.

new file mode 100644
--- /dev/null
+++ b/lib/strcasestr.c
@@ -0,0 +1,146 @@
+/* Case-insensitive searching in a string.
+   Copyright (C) 2005 Free Software Foundation, Inc.
+   Written by Bruno Haible <bruno@clisp.org>, 2005.
+
+   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 2, 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, write to the Free Software Foundation,
+   Inc., 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301, USA.  */
+
+#ifdef HAVE_CONFIG_H
+# include <config.h>
+#endif
+
+/* Specification.  */
+#include "strcasestr.h"
+
+#include <ctype.h>
+
+#if HAVE_MBRTOWC
+# include "mbuiter.h"
+#endif
+
+#define TOLOWER(Ch) (isupper (Ch) ? tolower (Ch) : (Ch))
+
+/* Find the first occurrence of NEEDLE in HAYSTACK, using case-insensitive
+   comparison.
+   Note: This function may, in multibyte locales, return success even if
+   strlen (haystack) < strlen (needle) !  */
+char *
+strcasestr (const char *haystack, const char *needle)
+{
+  /* Be careful not to look at the entire extent of haystack or needle
+     until needed.  This is useful because of these two cases:
+       - haystack may be very long, and a match of needle found early,
+       - needle may be very long, and not even a short initial segment of
+         needle may be found in haystack.  */
+#if HAVE_MBRTOWC
+  if (MB_CUR_MAX > 1)
+    {
+      mbui_iterator_t iter_needle;
+
+      mbui_init (iter_needle, needle);
+      if (mbui_avail (iter_needle))
+	{
+	  mbchar_t b;
+	  mbui_iterator_t iter_haystack;
+
+	  mb_copy (&b, &mbui_cur (iter_needle));
+	  if (b.wc_valid)
+	    b.wc = towlower (b.wc);
+
+	  mbui_init (iter_haystack, haystack);
+	  for (;; mbui_advance (iter_haystack))
+	    {
+	      mbchar_t c;
+
+	      if (!mbui_avail (iter_haystack))
+		/* No match.  */
+		return NULL;
+
+	      mb_copy (&c, &mbui_cur (iter_haystack));
+	      if (c.wc_valid)
+		c.wc = towlower (c.wc);
+	      if (mb_equal (c, b))
+		/* The first character matches.  */
+		{
+		  mbui_iterator_t rhaystack;
+		  mbui_iterator_t rneedle;
+
+		  memcpy (&rhaystack, &iter_haystack, sizeof (mbui_iterator_t));
+		  mbui_advance (rhaystack);
+
+		  mbui_init (rneedle, needle);
+		  if (!mbui_avail (rneedle))
+		    abort ();
+		  mbui_advance (rneedle);
+
+		  for (;; mbui_advance (rhaystack), mbui_advance (rneedle))
+		    {
+		      if (!mbui_avail (rneedle))
+			/* Found a match.  */
+			return (char *) haystack;
+		      if (!mbui_avail (rhaystack))
+			/* No match.  */
+			return NULL;
+		      if (!mb_caseequal (mbui_cur (rhaystack),
+					 mbui_cur (rneedle)))
+			/* Nothing in this round.  */
+			break;
+		    }
+		}
+	    }
+	}
+      else
+	return (char *) haystack;
+    }
+  else
+#endif
+    {
+      if (*needle != '\0')
+	{
+	  /* Speed up the following searches of needle by caching its first
+	     character.  */
+	  unsigned char b = TOLOWER ((unsigned char) *needle);
+
+	  needle++;
+	  for (;; haystack++)
+	    {
+	      if (*haystack == '\0')
+		/* No match.  */
+		return NULL;
+	      if (TOLOWER ((unsigned char) *haystack) == b)
+		/* The first character matches.  */
+		{
+		  const char *rhaystack = haystack + 1;
+		  const char *rneedle = needle;
+
+		  for (;; rhaystack++, rneedle++)
+		    {
+		      if (*rneedle == '\0')
+			/* Found a match.  */
+			return (char *) haystack;
+		      if (*rhaystack == '\0')
+			/* No match.  */
+			return NULL;
+		      if (TOLOWER ((unsigned char) *rhaystack)
+			  != TOLOWER ((unsigned char) *rneedle))
+			/* Nothing in this round.  */
+			break;
+		    }
+		}
+	    }
+	}
+      else
+	return (char *) haystack;
+    }
+}

new file mode 100644
--- /dev/null
+++ b/lib/strcasestr.h
@@ -0,0 +1,30 @@
+/* Case-insensitive searching in a string.
+   Copyright (C) 2005 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 2, 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, write to the Free Software Foundation,
+   Inc., 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301, USA.  */
+
+#ifdef __cplusplus
+extern "C" {
+#endif
+
+/* Find the first occurrence of NEEDLE in HAYSTACK, using case-insensitive
+   comparison.
+   Note: This function may, in multibyte locales, return success even if
+   strlen (haystack) < strlen (needle) !  */
+extern char *strcasestr (const char *haystack, const char *needle);
+
+#ifdef __cplusplus
+}
+#endif

--- a/m4/ChangeLog
+++ b/m4/ChangeLog
@@ -1,3 +1,7 @@
+2005-08-17  Bruno Haible  <bruno@clisp.org>
+
+	* strcasestr.m4: New file.
+
 2005-08-17  Bruno Haible  <bruno@clisp.org>
 
 	* strstr.m4 (gl_FUNC_STRSTR): Use the replacement function always.

new file mode 100644
--- /dev/null
+++ b/m4/strcasestr.m4
@@ -0,0 +1,19 @@
+# strcasestr.m4 serial 1
+dnl Copyright (C) 2005 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_STRCASESTR],
+[
+  dnl No known system has a strcasestr() function that works correctly in
+  dnl multibyte locales. Therefore we use our version always.
+  AC_LIBOBJ(strcasestr)
+  AC_DEFINE(strcasestr, rpl_strcasestr, [Define to rpl_strcasestr always.])
+  gl_PREREQ_STRCASESTR
+])
+
+# Prerequisites of lib/strcasestr.c.
+AC_DEFUN([gl_PREREQ_STRCASESTR], [
+  gl_FUNC_MBRTOWC
+])

new file mode 100644
--- /dev/null
+++ b/modules/strcasestr
@@ -0,0 +1,27 @@
+Description:
+strcasestr() function: case-insensitive search for a substring in a string.
+
+Files:
+lib/strcasestr.h
+lib/strcasestr.c
+m4/strcasestr.m4
+m4/mbrtowc.m4
+
+Depends-on:
+mbuiter
+
+configure.ac:
+gl_FUNC_STRCASESTR
+
+Makefile.am:
+lib_SOURCES += strcasestr.h
+
+Include:
+"strcasestr.h"
+
+License:
+LGPL
+
+Maintainer:
+Bruno Haible
+