From 3081860737968ae9d461c1dc5ab2e31f94918d35 Mon Sep 17 00:00:00 2001
From: =?UTF-8?q?P=C3=A1draig=20Brady?= <address@hidden>
Date: Sun, 20 May 2018 22:11:12 -0700
Subject: [PATCH] wchar-single: a new module to enable optimizations in wchar
 replacements

* lib/mbrtowc.c (mbrtowc): Only check locale_charset() once if
GNULIB_WCHAR_SINGLE is enabled.
* lib/wcwidth.c (wcwidth): Likewise.
---
 lib/mbrtowc.c        | 14 ++++++++++++--
 lib/wcwidth.c        | 15 +++++++++++++--
 modules/wchar-single | 21 +++++++++++++++++++++
 3 files changed, 46 insertions(+), 4 deletions(-)
 create mode 100644 modules/wchar-single

diff --git a/lib/mbrtowc.c b/lib/mbrtowc.c
index 22ac2c4..dc3597f 100644
--- a/lib/mbrtowc.c
+++ b/lib/mbrtowc.c
@@ -138,9 +138,19 @@ mbrtowc (wchar_t *pwc, const char *s, size_t n, mbstate_t *ps)
         goto invalid;
       /* Here MB_CUR_MAX > 1 and 0 < m < 4.  */
       {
-        const char *encoding = locale_charset ();
+        static int utf8_charset = -1;
+        static const char *encoding;
 
-        if (STREQ_OPT (encoding, "UTF-8", 'U', 'T', 'F', '-', '8', 0, 0, 0, 0))
+# if GNULIB_WCHAR_SINGLE
+        if (utf8_charset == -1)
+# endif
+          {
+            encoding = locale_charset ();
+            utf8_charset = STREQ_OPT (encoding,
+                                      "UTF-8", 'U', 'T', 'F', '-', '8', 0, 0, 0 ,0);
+          }
+
+        if (utf8_charset)
           {
             /* Cf. unistr/u8-mblen.c.  */
             unsigned char c = (unsigned char) p[0];
diff --git a/lib/wcwidth.c b/lib/wcwidth.c
index 5fb090e..d03a50f 100644
--- a/lib/wcwidth.c
+++ b/lib/wcwidth.c
@@ -30,9 +30,20 @@ int
 wcwidth (wchar_t wc)
 #undef wcwidth
 {
+  static int utf8_charset = -1;
+  static const char *encoding;
+
+#if GNULIB_WCHAR_SINGLE
+  if (utf8_charset == -1)
+#endif
+    {
+      encoding = locale_charset ();
+      utf8_charset = STREQ_OPT (encoding,
+                                "UTF-8", 'U', 'T', 'F', '-', '8', 0, 0, 0 ,0);
+    }
+
   /* In UTF-8 locales, use a Unicode aware width function.  */
-  const char *encoding = locale_charset ();
-  if (STREQ_OPT (encoding, "UTF-8", 'U', 'T', 'F', '-', '8', 0, 0, 0 ,0))
+  if (utf8_charset)
     {
       /* We assume that in a UTF-8 locale, a wide character is the same as a
          Unicode character.  */
diff --git a/modules/wchar-single b/modules/wchar-single
new file mode 100644
index 0000000..e047de0
--- /dev/null
+++ b/modules/wchar-single
@@ -0,0 +1,21 @@
+Description:
+Enable more efficient wchar replacements, where we know
+the locale charset will not change between calls.
+
+Files:
+
+Depends-on:
+wchar
+
+configure.ac:
+gl_MODULE_INDICATOR([wchar-single])
+
+Makefile.am:
+
+Include:
+
+License:
+LGPLv2+
+
+Maintainer:
+all
-- 
2.9.3