lib/unigbrk/u8-grapheme-prev.c

   1 /* Previous grapheme cluster function.
   2    Copyright (C) 2010-2017 Free Software Foundation, Inc.
   3    Written by Ben Pfaff <blp@cs.stanford.edu>, 2010.
   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 <https://www.gnu.org/licenses/>.  */
  17
  18 #include <config.h>
  19
  20 /* Specification.  */
  21 #include "unigbrk.h"
  22
  23 #include "unistr.h"
  24
  25 const uint8_t *
  26 u8_grapheme_prev (const uint8_t *s, const uint8_t *start)
  27 {
  28   ucs4_t next;
  29
  30   if (s == start)
  31     return NULL;
  32
  33   s = u8_prev (&next, s, start);
  34   while (s != start)
  35     {
  36       const uint8_t *prev_s;
  37       ucs4_t prev;
  38
  39       prev_s = u8_prev (&prev, s, start);
  40       if (prev_s == NULL)
  41         {
  42           /* Ill-formed UTF-8 encoding. */
  43           return start;
  44         }
  45
  46       if (uc_is_grapheme_break (prev, next))
  47         break;
  48
  49       s = prev_s;
  50       next = prev;
  51     }
  52
  53   return s;
  54 }