unigbrk: New modules for grapheme clusters.

[gnulib.git] / lib / unigbrk / u32-grapheme-prev.c

diff --git a/lib/unigbrk/u32-grapheme-prev.c b/lib/unigbrk/u32-grapheme-prev.c
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+++ b/lib/unigbrk/u32-grapheme-prev.c
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+/* Previous grapheme cluster function.
+   Copyright (C) 2010 Free Software Foundation, Inc.
+   Written by Ben Pfaff <blp@cs.stanford.edu>, 2010.
+
+   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 "unigbrk.h"
+
+#include "unistr.h"
+
+const uint32_t *
+u32_grapheme_prev (const uint32_t *s, const uint32_t *start)
+{
+  ucs4_t next;
+
+  if (s == start)
+    return NULL;
+
+  u32_prev (&next, s, start);
+  for (s--; s != start; s--)
+    {
+      ucs4_t prev;
+
+      if (u32_prev (&prev, s, start) == NULL)
+        {
+          /* Ill-formed UTF-32 encoding. */
+          return start;
+        }
+
+      if (uc_is_grapheme_cluster_break (prev, next))
+        break;
+
+      next = prev;
+    }
+
+  return s;
+}