1 files changed, 101 insertions, 0 deletions
diff --git a/lib/unicase/u-prefix-context.h b/lib/unicase/u-prefix-context.h
new file mode 100644
index 00000000..b30ed6b1
--- /dev/null
+++ b/lib/unicase/u-prefix-context.h
@@ -0,0 +1,101 @@
+/* Case-mapping context of prefix UTF-8/UTF-16/UTF-32 string.
+   Copyright (C) 2009-2018 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 either:
+
+     * 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.
+
+   or
+
+     * the GNU General Public License as published by the Free
+       Software Foundation; either version 2 of the License, or (at your
+       option) any later version.
+
+   or both in parallel, as here.
+   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 <https://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
+}