1  /* Determine the number of screen columns needed for a character.
       2     Copyright (C) 2006-2007, 2010-2023 Free Software Foundation, Inc.
       3  
       4     This file is free software: you can redistribute it and/or modify
       5     it under the terms of the GNU Lesser General Public License as
       6     published by the Free Software Foundation; either version 2.1 of the
       7     License, or (at your option) any later version.
       8  
       9     This file is distributed in the hope that it will be useful,
      10     but WITHOUT ANY WARRANTY; without even the implied warranty of
      11     MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
      12     GNU Lesser General Public License for more details.
      13  
      14     You should have received a copy of the GNU Lesser General Public License
      15     along with this program.  If not, see <https://www.gnu.org/licenses/>.  */
      16  
      17  #include <config.h>
      18  
      19  /* Specification.  */
      20  #include <wchar.h>
      21  
      22  /* Get iswprint.  */
      23  #include <wctype.h>
      24  
      25  #include "localcharset.h"
      26  #include "streq.h"
      27  #include "uniwidth.h"
      28  
      29  /* Returns 1 if the current locale is an UTF-8 locale, 0 otherwise.  */
      30  static inline int
      31  is_locale_utf8 (void)
      32  {
      33    const char *encoding = locale_charset ();
      34    return STREQ_OPT (encoding, "UTF-8", 'U', 'T', 'F', '-', '8', 0, 0, 0, 0);
      35  }
      36  
      37  #if GNULIB_WCHAR_SINGLE_LOCALE
      38  /* When we know that the locale does not change, provide a speedup by
      39     caching the value of is_locale_utf8.  */
      40  static int cached_is_locale_utf8 = -1;
      41  static inline int
      42  is_locale_utf8_cached (void)
      43  {
      44    if (cached_is_locale_utf8 < 0)
      45      cached_is_locale_utf8 = is_locale_utf8 ();
      46    return cached_is_locale_utf8;
      47  }
      48  #else
      49  /* By default, don't make assumptions, hence no caching.  */
      50  # define is_locale_utf8_cached is_locale_utf8
      51  #endif
      52  
      53  int
      54  wcwidth (wchar_t wc)
      55  #undef wcwidth
      56  {
      57    /* In UTF-8 locales, use a Unicode aware width function.  */
      58    if (is_locale_utf8_cached ())
      59      {
      60        /* We assume that in a UTF-8 locale, a wide character is the same as a
      61           Unicode character.  */
      62        return uc_width (wc, "UTF-8");
      63      }
      64    else
      65      {
      66        /* Otherwise, fall back to the system's wcwidth function.  */
      67  #if HAVE_WCWIDTH
      68        return wcwidth (wc);
      69  #else
      70        return wc == 0 ? 0 : iswprint (wc) ? 1 : -1;
      71  #endif
      72      }
      73  }