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libstdc++: Avoid -Wtype-limits warnings in locale/gnu/ctype_members.cc

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On targets where wchar_t is unsigned we get warnings during the
libstdc++ build:

ctype_members.cc: In member function ‘virtual char std::ctype<wchar_t>::do_narrow(wchar_t, char) const’:
ctype_members.cc:224:14: warning: comparison of unsigned expression in ‘>= 0’ is always true [-Wtype-limits]
  224 |     if (__wc >= 0 && __wc < 128 && _M_narrow_ok)
      |         ~~~~~^~~~
ctype_members.cc: In member function ‘virtual const wchar_t* std::ctype<wchar_t>::do_narrow(const wchar_t*, const wchar_t*, char, char*) const’:
ctype_members.cc:247:21: warning: comparison of unsigned expression in ‘>= 0’ is always true [-Wtype-limits]
  247 |           if (*__lo >= 0 && *__lo < 128)
      |               ~~~~~~^~~~

This introduces a helper function that converts the wchar_t to an
unsigned type and then does the comparison. This means the comparison is
not target-dependent, and there's no more warning.

libstdc++-v3/ChangeLog:

	* config/locale/gnu/ctype_members.cc (use_table): New function.
	(ctype<wchar_t>::do_narrow): Use use_table.

Reviewed-by: Tomasz Kamiński <tkaminsk@redhat.com>
This commit is contained in:
Jonathan Wakely
2026-01-23 14:04:26 +00:00
committed by Jonathan Wakely
parent bb5ebc9373
commit 975025de35
1 changed files with 11 additions and 2 deletions
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13
libstdc++-v3/config/locale/gnu/ctype_members.cc
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@@ -217,11 +217,20 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION
return __hi;
}
// True if c can be looked up in _M_narrow.
[[gnu::always_inline]]
static inline bool
use_table(wchar_t c)
{
using U = std::make_unsigned<wchar_t>::type;
return U(c) < 128;
}
char
ctype<wchar_t>::
do_narrow(wchar_t __wc, char __dfault) const
{
if (__wc >= 0 && __wc < 128 && _M_narrow_ok)
if (use_table(__wc) && _M_narrow_ok)
return _M_narrow[__wc];
#if __GLIBC__ > 2 || (__GLIBC__ == 2 && __GLIBC_MINOR__ > 2)
__c_locale __old = __uselocale(_M_c_locale_ctype);
@@ -244,7 +253,7 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION
if (_M_narrow_ok)
while (__lo < __hi)
{
if (*__lo >= 0 && *__lo < 128)
if (use_table(*__lo))
*__dest = _M_narrow[*__lo];
else
{