1/* Iterate over previous character in UTF-16 string.
2   Copyright (C) 2002, 2006-2007, 2009-2010 Free Software Foundation, Inc.
3   Written by Bruno Haible <bruno@clisp.org>, 2002.
4
5   This program is free software: you can redistribute it and/or modify it
6   under the terms of the GNU Lesser General Public License as published
7   by the Free Software Foundation; either version 3 of the License, or
8   (at your option) any later version.
9
10   This program is distributed in the hope that it will be useful,
11   but WITHOUT ANY WARRANTY; without even the implied warranty of
12   MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
13   Lesser General Public License for more details.
14
15   You should have received a copy of the GNU Lesser General Public License
16   along with this program.  If not, see <http://www.gnu.org/licenses/>.  */
17
18#include <config.h>
19
20/* Specification.  */
21#include "unistr.h"
22
23const uint16_t *
24u16_prev (ucs4_t *puc, const uint16_t *s, const uint16_t *start)
25{
26  /* Keep in sync with unistr.h and utf16-ucs4.c.  */
27  if (s != start)
28    {
29      uint16_t c_1 = s[-1];
30
31      if (c_1 < 0xd800 || c_1 >= 0xe000)
32        {
33          *puc = c_1;
34          return s - 1;
35        }
36#if CONFIG_UNICODE_SAFETY
37      if (c_1 >= 0xdc00)
38#endif
39        if (s - 1 != start)
40          {
41            uint16_t c_2 = s[-2];
42
43#if CONFIG_UNICODE_SAFETY
44            if (c_2 >= 0xd800 && c_2 < 0xdc00)
45#endif
46              {
47                *puc = 0x10000 + ((c_2 - 0xd800) << 10) + (c_1 - 0xdc00);
48                return s - 2;
49              }
50          }
51    }
52  return NULL;
53}
54