1 files changed, 53 insertions, 0 deletions
diff --git a/lib/unistr/u16-prev.c b/lib/unistr/u16-prev.c
new file mode 100644
index 00000000..3beecf01
--- /dev/null
+++ b/lib/unistr/u16-prev.c
@@ -0,0 +1,53 @@
+/* Iterate over previous character in UTF-16 string.
+   Copyright (C) 2002, 2006-2007 Free Software Foundation, Inc.
+   Written by Bruno Haible <bruno@clisp.org>, 2002.
+
+   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 "unistr.h"
+
+const uint16_t *
+u16_prev (ucs4_t *puc, const uint16_t *s, const uint16_t *start)
+{
+  /* Keep in sync with unistr.h and utf16-ucs4.c.  */
+  if (s != start)
+    {
+      uint16_t c_1 = s[-1];
+
+      if (c_1 < 0xd800 || c_1 >= 0xe000)
+	{
+	  *puc = c_1;
+	  return s - 1;
+	}
+#if CONFIG_UNICODE_SAFETY
+      if (c_1 >= 0xdc00)
+#endif
+	if (s - 1 != start)
+	  {
+	    uint16_t c_2 = s[-2];
+
+#if CONFIG_UNICODE_SAFETY
+	    if (c_2 >= 0xd800 && c_2 < 0xdc00)
+#endif
+	      {
+		*puc = 0x10000 + ((c_2 - 0xd800) << 10) + (c_1 - 0xdc00);
+		return s - 2;
+	      }
+	  }
+    }
+  return NULL;
+}