kc3-lang/gnulib/lib/unistr/u8-prev.c

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• Hash : 32a72f45
  Author :
  Date : 2023-01-01T01:14:21
  

  maint: run 'make update-copyright'
  

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• lib/unistr/u8-prev.c

• /* Iterate over previous character in UTF-8 string.
     Copyright (C) 2002, 2006-2007, 2009-2023 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 < 0xf8
                              && (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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