[gcc r10-10560] libstdc++: Do not use std::isdigit in <charconv> [PR103911]

[Jonathan Wakely]

https://gcc.gnu.org/g:b596c35a4ed0143e84422449020296b43a655de7

commit r10-10560-gb596c35a4ed0143e84422449020296b43a655de7
Author: Jonathan Wakely <jwakely@redhat.com>
Date:   Wed Jan 5 16:25:47 2022 +0000

    libstdc++: Do not use std::isdigit in <charconv> [PR103911]
    
    This avoids a potential race condition if std::setlocale is used
    concurrently with std::from_chars.
    
    libstdc++-v3/ChangeLog:
    
            PR libstdc++/103911
            * include/std/charconv (__from_chars_alpha_to_num): Return
            char instead of unsigned char. Change invalid return value to
            127 instead of using numeric trait.
            (__from_chars_alnum): Fix comment. Do not use std::isdigit.
            Change type of variable to char.
    
    (cherry picked from commit c83ecfbe74a5cf107642b9c5e1680b548ff1a0e1)

Diff:
---
 libstdc++-v3/include/std/charconv | 11 +++++------
 1 file changed, 5 insertions(+), 6 deletions(-)

diff --git a/libstdc++-v3/include/std/charconv b/libstdc++-v3/include/std/charconv
index daad423570a..12fa39cd13e 100644
--- a/libstdc++-v3/include/std/charconv
+++ b/libstdc++-v3/include/std/charconv
@@ -39,7 +39,6 @@
 
 #include <type_traits>
 #include <bit>			// for __bit_width
-#include <cctype>		// for isdigit
 #include <bits/charconv.h>	// for __to_chars_len, __to_chars_10_impl
 #include <bits/error_constants.h> // for std::errc
 #include <ext/numeric_traits.h>
@@ -465,7 +464,7 @@ namespace __detail
       return true;
     }
 
-  constexpr unsigned char
+  constexpr char
   __from_chars_alpha_to_num(char __c)
   {
     switch (__c)
@@ -549,10 +548,10 @@ namespace __detail
     case 'Z':
       return 35;
     }
-    return __gnu_cxx::__int_traits<unsigned char>::__max;
+    return 127;
   }
 
-  /// std::from_chars implementation for integers in bases 11 to 26.
+  /// std::from_chars implementation for integers in bases 11 to 36.
   template<typename _Tp>
     bool
     __from_chars_alnum(const char*& __first, const char* __last, _Tp& __val,
@@ -561,8 +560,8 @@ namespace __detail
       bool __valid = true;
       while (__first != __last)
 	{
-	  unsigned char __c = *__first;
-	  if (std::isdigit(__c))
+	  char __c = *__first;
+	  if ('0' <= __c && __c <= '9') // isdigit
 	    __c -= '0';
 	  else
 	    {