lib/unigbrk/u32-grapheme-prev.c

   1 /* Previous grapheme cluster function.
   2    Copyright (C) 2010-2025 Free Software Foundation, Inc.
   3    Written by Ben Pfaff <blp@cs.stanford.edu>, 2010.
   4
   5    This file is free software.
   6    It is dual-licensed under "the GNU LGPLv3+ or the GNU GPLv2+".
   7    You can redistribute it and/or modify it under either
   8      - the terms of the GNU Lesser General Public License as published
   9        by the Free Software Foundation, either version 3, or (at your
  10        option) any later version, or
  11      - the terms of the GNU General Public License as published by the
  12        Free Software Foundation; either version 2, or (at your option)
  13        any later version, or
  14      - the same dual license "the GNU LGPLv3+ or the GNU GPLv2+".
  15
  16    This file is distributed in the hope that it will be useful,
  17    but WITHOUT ANY WARRANTY; without even the implied warranty of
  18    MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
  19    Lesser General Public License and the GNU General Public License
  20    for more details.
  21
  22    You should have received a copy of the GNU Lesser General Public
  23    License and of the GNU General Public License along with this
  24    program.  If not, see <https://www.gnu.org/licenses/>.  */
  25
  26 #include <config.h>
  27
  28 /* Specification.  */
  29 #include "unigbrk.h"
  30
  31 #include "unistr.h"
  32
  33 const uint32_t *
  34 u32_grapheme_prev (const uint32_t *s, const uint32_t *start)
  35 {
  36   ucs4_t next;
  37
  38   if (s == start)
  39     return NULL;
  40
  41   u32_prev (&next, s, start);
  42   for (s--; s != start; s--)
  43     {
  44       ucs4_t prev;
  45
  46       if (u32_prev (&prev, s, start) == NULL)
  47         {
  48           /* Ill-formed UTF-32 encoding. */
  49           return start;
  50         }
  51
  52       if (uc_is_grapheme_break (prev, next))
  53         break;
  54
  55       next = prev;
  56     }
  57
  58   return s;
  59 }