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/* Iterate over previous character in UTF-16 string.
Copyright (C) 2002, 2006-2007, 2009-2024 Free Software Foundation, Inc.
Written by Bruno Haible <bruno@clisp.org>, 2002.
This file is free software.
It is dual-licensed under "the GNU LGPLv3+ or the GNU GPLv2+".
You can redistribute it and/or modify it under either
- the terms of the GNU Lesser General Public License as published
by the Free Software Foundation, either version 3, or (at your
option) any later version, or
- the terms of the GNU General Public License as published by the
Free Software Foundation; either version 2, or (at your option)
any later version, or
- the same dual license "the GNU LGPLv3+ or the GNU GPLv2+".
This file 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 and the GNU General Public License
for more details.
You should have received a copy of the GNU Lesser General Public
License and of the GNU General Public License along with this
program. If not, see <https://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 (c_1 >= 0xdc00)
if (s - 1 != start)
{
uint16_t c_2 = s[-2];
if (c_2 >= 0xd800 && c_2 < 0xdc00)
{
*puc = 0x10000 + ((c_2 - 0xd800) << 10) + (c_1 - 0xdc00);
return s - 2;
}
}
}
return NULL;
}
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