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-rw-r--r--lib/unistr/u16-prev.c53
1 files changed, 53 insertions, 0 deletions
diff --git a/lib/unistr/u16-prev.c b/lib/unistr/u16-prev.c
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+++ b/lib/unistr/u16-prev.c
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+/* 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;
+}