From: Jonathan Wakely <jwakely@redhat.com>
Date: Tue, 14 Nov 2023 10:56:57 +0000 (+0000)
Subject: libstdc++: Fix <charconv> uses of signed types with <bit> functions
X-Git-Tag: basepoints/gcc-15~4673
X-Git-Url: http://git.ipfire.org/?a=commitdiff_plain;h=1c15303375f7089ff985b085ab877b11ebfbc4b7;p=thirdparty%2Fgcc.git

libstdc++: Fix <charconv> uses of signed types with <bit> functions

In <charconv> we pass the int __base parameter to our internal versions
of <bit> functions, __bit_width and __countr_zero. Those functions are
only defined for unsigned types, so we need to convert the base to
unsigned. The base must be in the range [2,36] so we can mask off the
low bits and then convert that to unsigned, so that we don't need to
care about negative values becoming large unsigned values.

libstdc++-v3/ChangeLog:

	* include/std/charconv (__from_chars_pow2_base): Convert base to
	unsigned for call to __countr_zero.
	(__from_chars_alnum): Likewise for call to __bit_width.
---

diff --git a/libstdc++-v3/include/std/charconv b/libstdc++-v3/include/std/charconv
index 6cb7fecff870..54632968f5a0 100644
--- a/libstdc++-v3/include/std/charconv
+++ b/libstdc++-v3/include/std/charconv
@@ -465,7 +465,7 @@ namespace __detail
 
       // __glibcxx_assert((__base & (__base - 1)) == 0);
       // __glibcxx_assert(_DecOnly ? __base <= 8 : __base <= 32);
-      const int __log2_base = __countr_zero(__base);
+      const int __log2_base = __countr_zero(unsigned(__base & 0x3f));
 
       const ptrdiff_t __len = __last - __first;
       ptrdiff_t __i = 0;
@@ -517,9 +517,9 @@ namespace __detail
     __from_chars_alnum(const char*& __first, const char* __last, _Tp& __val,
 		       int __base)
     {
-      // __glibcxx_assert(!_DecOnly || __base <= 10);
+      // __glibcxx_assert(_DecOnly ? __base <= 10 : __base <= 36);
 
-      const int __bits_per_digit = __bit_width(__base);
+      const int __bits_per_digit = __bit_width(unsigned(__base & 0x3f));
       int __unused_bits_lower_bound = __gnu_cxx::__int_traits<_Tp>::__digits;
       for (; __first != __last; ++__first)
 	{