lib/wcwidth.c

   1 /* Determine the number of screen columns needed for a character.
   2    Copyright (C) 2006-2007, 2010-2024 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 }