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diff --git a/lib/unistr/u16-strmbtouc.c b/lib/unistr/u16-strmbtouc.c
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+/* Look at first character in UTF-16 string.
+ Copyright (C) 1999-2000, 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"
+
+int
+u16_strmbtouc (ucs4_t *puc, const uint16_t *s)
+{
+ /* Keep in sync with unistr.h and utf16-ucs4.c. */
+ uint16_t c = *s;
+
+ if (c < 0xd800 || c >= 0xe000)
+ {
+ *puc = c;
+ return (c != 0 ? 1 : 0);
+ }
+#if CONFIG_UNICODE_SAFETY
+ if (c < 0xdc00)
+#endif
+ {
+#if CONFIG_UNICODE_SAFETY
+ if (s[1] >= 0xdc00 && s[1] < 0xe000)
+#else
+ if (s[1] != 0)
+#endif
+ {
+ *puc = 0x10000 + ((c - 0xd800) << 10) + (s[1] - 0xdc00);
+ return 2;
+ }
+ }
+ /* invalid or incomplete multibyte character */
+ return -1;
+}