[gcc r11-4844] libstdc++: Improve comment on _Power_of_2 helper function

[gcc r11-4844] libstdc++: Improve comment on _Power_of_2 helper function

[Jonathan Wakely]

https://gcc.gnu.org/g:b2b85163731e8647542f2f7561bd4c69ae5f5f2a

commit r11-4844-gb2b85163731e8647542f2f7561bd4c69ae5f5f2a
Author: Jonathan Wakely <jwakely@redhat.com>
Date:   Mon Nov 9 14:32:45 2020 +0000

    libstdc++: Improve comment on _Power_of_2 helper function
    
    libstdc++-v3/ChangeLog:
    
            * include/bits/uniform_int_dist.h (__detail::_Power_of_2):
            Document that true result for zero is intentional.

Diff:
---
 libstdc++-v3/include/bits/uniform_int_dist.h | 4 +++-
 1 file changed, 3 insertions(+), 1 deletion(-)

diff --git a/libstdc++-v3/include/bits/uniform_int_dist.h b/libstdc++-v3/include/bits/uniform_int_dist.h
index 8f02b85c9bb..4169f705c2a 100644
--- a/libstdc++-v3/include/bits/uniform_int_dist.h
+++ b/libstdc++-v3/include/bits/uniform_int_dist.h
@@ -56,7 +56,9 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION
 
   namespace __detail
   {
-    /* Determine whether number is a power of 2.  */
+    // Determine whether number is a power of two.
+    // This is true for zero, which is OK because we want _Power_of_2(n+1)
+    // to be true if n==numeric_limits<_Tp>::max() and so n+1 wraps around.
     template<typename _Tp>
       constexpr bool
       _Power_of_2(_Tp __x)