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/* Iterate over previous character in UTF-8 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: 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 2.1 of the
License, or (at your option) any later version.
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 for more details.
You should have received a copy of the GNU Lesser General Public License
along with this program. If not, see <https://www.gnu.org/licenses/>. */
#include <config.h>
/* Specification. */
#include "unistr.h"
const uint8_t *
u8_prev (ucs4_t *puc, const uint8_t *s, const uint8_t *start)
{
/* Keep in sync with unistr.h and u8-mbtouc-aux.c. */
if (s != start)
{
uint8_t c_1 = s[-1];
if (c_1 < 0x80)
{
*puc = c_1;
return s - 1;
}
if ((c_1 ^ 0x80) < 0x40)
if (s - 1 != start)
{
uint8_t c_2 = s[-2];
if (c_2 >= 0xc2 && c_2 < 0xe0)
{
*puc = ((unsigned int) (c_2 & 0x1f) << 6)
| (unsigned int) (c_1 ^ 0x80);
return s - 2;
}
if ((c_2 ^ 0x80) < 0x40)
if (s - 2 != start)
{
uint8_t c_3 = s[-3];
if (c_3 >= 0xe0 && c_3 < 0xf0
&& (c_3 >= 0xe1 || c_2 >= 0xa0)
&& (c_3 != 0xed || c_2 < 0xa0))
{
*puc = ((unsigned int) (c_3 & 0x0f) << 12)
| ((unsigned int) (c_2 ^ 0x80) << 6)
| (unsigned int) (c_1 ^ 0x80);
return s - 3;
}
if ((c_3 ^ 0x80) < 0x40)
if (s - 3 != start)
{
uint8_t c_4 = s[-4];
if (c_4 >= 0xf0 && c_4 <= 0xf4
&& (c_4 >= 0xf1 || c_3 >= 0x90)
&& (c_4 < 0xf4 || (/* c_4 == 0xf4 && */ c_3 < 0x90)))
{
*puc = ((unsigned int) (c_4 & 0x07) << 18)
| ((unsigned int) (c_3 ^ 0x80) << 12)
| ((unsigned int) (c_2 ^ 0x80) << 6)
| (unsigned int) (c_1 ^ 0x80);
return s - 4;
}
}
}
}
}
return NULL;
}
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