--- a/ChangeLog
+++ b/ChangeLog
@@ -1,5 +1,11 @@
 2009-06-29  Bruno Haible  <bruno@clisp.org>
 
+	New module 'unicase/u8-prefix-context'.
+	* lib/unicase/u8-prefix-context.c: New file.
+	* lib/unicase/u-prefix-context.h: New file.
+	* lib/unicase/context.h: New file.
+	* modules/unicase/u8-prefix-context: New file.
+
 	New module 'unicase/empty-prefix-context'.
 	* lib/unicase/empty-prefix-context.c: New file.
 	* modules/unicase/empty-prefix-context: New file.

new file mode 100644
--- /dev/null
+++ b/lib/unicase/context.h
@@ -0,0 +1,63 @@
+/* Case-mapping contexts of UTF-8/UTF-16/UTF-32 substring.
+   Copyright (C) 2009 Free Software Foundation, Inc.
+   Written by Bruno Haible <bruno@clisp.org>, 2009.
+
+   This program 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 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
+   Lesser General Public License for more details.
+
+   You should have received a copy of the GNU Lesser General Public License
+   along with this program.  If not, see <http://www.gnu.org/licenses/>.  */
+
+
+/* The context of a prefix string combines the information of the "Before C"
+   conditions of the Unicode Standard,
+   <http://www.unicode.org/versions/Unicode5.0.0/ch03.pdf>, section 3.13,
+   table 3-14 "Context Specification for Casing".
+
+   casing_prefix_context_t contains the following fields:
+
+     // Helper for evaluating the FINAL_SIGMA condition:
+     //  Last character that was not case-ignorable.
+     ucs4_t last_char_except_ignorable;
+
+     // Helper for evaluating the AFTER_SOFT_DOTTED and AFTER_I conditions:
+     // Last character that was of combining class 230 ("Above") or 0.
+     ucs4_t last_char_normal_or_above;
+
+   Three bits would be sufficient to carry the context information, but
+   that would require to invoke uc_is_cased and uc_is_property_soft_dotted
+   ahead of time, more often than actually needed.  */
+
+
+/* The context of a suffix string combines the information of the "After C"
+   conditions of the Unicode Standard,
+   <http://www.unicode.org/versions/Unicode5.0.0/ch03.pdf>, section 3.13,
+   table 3-14 "Context Specification for Casing".
+
+   casing_suffix_context_t contains the following fields:
+
+     // For evaluating the FINAL_SIGMA condition:
+     // Bit 0 is set if the suffix starts with a sequence consisting of a
+     // case-ignorable sequence and then a cased letter.
+     //
+     // For evaluating the MORE_ABOVE condition:
+     // Bit 1 is set if the suffix contains a character of combining class
+     // 230 (Above) with no character of combining class 0 or 230 (Above)
+     // before it.
+     //
+     // For evaluating the BEFORE_DOT condition:
+     // Bit 2 is set if the suffix contains a COMBINING DOT ABOVE (U+0307)
+     // with no character of combining class 0 or 230 (Above) before it.
+     //
+     uint32_t bits;
+ */
+#define SCC_FINAL_SIGMA_MASK 1
+#define SCC_MORE_ABOVE_MASK  2
+#define SCC_BEFORE_DOT_MASK  4

new file mode 100644
--- /dev/null
+++ b/lib/unicase/u-prefix-context.h
@@ -0,0 +1,92 @@
+/* Case-mapping context of prefix UTF-8/UTF-16/UTF-32 string.
+   Copyright (C) 2009 Free Software Foundation, Inc.
+   Written by Bruno Haible <bruno@clisp.org>, 2009.
+
+   This program 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 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
+   Lesser General Public License for more details.
+
+   You should have received a copy of the GNU Lesser General Public License
+   along with this program.  If not, see <http://www.gnu.org/licenses/>.  */
+
+casing_prefix_context_t
+FUNC1 (const UNIT *s, size_t n)
+{
+  return FUNC2 (s, n, unicase_empty_prefix_context);
+}
+
+casing_prefix_context_t
+FUNC2 (const UNIT *s, size_t n, casing_prefix_context_t a_context)
+{
+#if 0
+  /* Forward iteration.  Slow for long strings.  */
+  casing_prefix_context_t context = a_context;
+  const UNIT *s_end = s + n;
+
+  while (s < s_end)
+    {
+      ucs4_t uc;
+      int count = U_MBTOUC_UNSAFE (&uc, s, s_end - s);
+
+      if (!uc_is_case_ignorable (uc))
+	context.last_char_except_ignorable = uc;
+
+      {
+	int ccc = uc_combining_class (uc);
+	if (ccc == UC_CCC_A || ccc == UC_CCC_NR)
+	  context.last_char_normal_or_above = uc;
+      }
+
+      s += count;
+    }
+
+  return context;
+#else
+  /* Iterate backwards, only as far as needed.  */
+  casing_prefix_context_t context;
+  ucs4_t last_char_except_ignorable = (ucs4_t)(-1);
+  ucs4_t last_char_normal_or_above = (ucs4_t)(-1);
+  const UNIT *p = s + n;
+
+  for (;;)
+    {
+      ucs4_t uc;
+      p = U_PREV (&uc, p, s);
+      if (p == NULL)
+	break;
+
+      if (last_char_except_ignorable == (ucs4_t)(-1))
+	{
+	  if (!uc_is_case_ignorable (uc))
+	    last_char_except_ignorable = uc;
+	}
+
+      if (last_char_normal_or_above == (ucs4_t)(-1))
+	{
+	  int ccc = uc_combining_class (uc);
+	  if (ccc == UC_CCC_A || ccc == UC_CCC_NR)
+	    last_char_normal_or_above = uc;
+	}
+
+      if (last_char_except_ignorable != (ucs4_t)(-1)
+	  && last_char_normal_or_above != (ucs4_t)(-1))
+	break;
+    }
+  context.last_char_except_ignorable =
+    (last_char_except_ignorable != (ucs4_t)(-1)
+     ? last_char_except_ignorable
+     : a_context.last_char_except_ignorable);
+  context.last_char_normal_or_above =
+    (last_char_normal_or_above != (ucs4_t)(-1)
+     ? last_char_normal_or_above
+     : a_context.last_char_normal_or_above);
+
+  return context;
+#endif
+}

new file mode 100644
--- /dev/null
+++ b/lib/unicase/u8-prefix-context.c
@@ -0,0 +1,33 @@
+/* Case-mapping context of prefix UTF-8 string.
+   Copyright (C) 2009 Free Software Foundation, Inc.
+   Written by Bruno Haible <bruno@clisp.org>, 2009.
+
+   This program 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 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
+   Lesser General Public License for more details.
+
+   You should have received a copy of the GNU Lesser General Public License
+   along with this program.  If not, see <http://www.gnu.org/licenses/>.  */
+
+#include <config.h>
+
+/* Specification.  */
+#include "unicase.h"
+
+#include "unictype.h"
+#include "unistr.h"
+#include "caseprop.h"
+#include "context.h"
+
+#define FUNC1 u8_casing_prefix_context
+#define FUNC2 u8_casing_prefixes_context
+#define UNIT uint8_t
+#define U_MBTOUC_UNSAFE u8_mbtouc_unsafe
+#define U_PREV u8_prev
+#include "u-prefix-context.h"

new file mode 100644
--- /dev/null
+++ b/modules/unicase/u8-prefix-context
@@ -0,0 +1,30 @@
+Description:
+Case-mapping context of prefix UTF-8 string.
+
+Files:
+lib/unicase/u8-prefix-context.c
+lib/unicase/u-prefix-context.h
+lib/unicase/context.h
+
+Depends-on:
+unicase/base
+unicase/empty-prefix-context
+unicase/ignorable
+unictype/combining-class
+unistr/u8-mbtouc-unsafe
+unistr/u8-prev
+
+configure.ac:
+
+Makefile.am:
+lib_SOURCES += unicase/u8-prefix-context.c
+
+Include:
+"unicase.h"
+
+License:
+LGPL
+
+Maintainer:
+Bruno Haible
+