[gcc r14-9001] libstdc++: Use unsigned division in std::rotate [PR113811]

[gcc r14-9001] libstdc++: Use unsigned division in std::rotate [PR113811]

[Jonathan Wakely]

https://gcc.gnu.org/g:4d819db7f229a23cb15ef68f310e0bb51d201c45

commit r14-9001-g4d819db7f229a23cb15ef68f310e0bb51d201c45
Author: Jonathan Wakely <jwakely@redhat.com>
Date:   Thu Feb 8 15:40:32 2024 +0000

    libstdc++: Use unsigned division in std::rotate [PR113811]
    
    Signed 64-bit division is much slower than unsigned, so cast the n and
    k values to unsigned before doing n %= k. We know this is safe because
    neither value can be negative.
    
    libstdc++-v3/ChangeLog:
    
            PR libstdc++/113811
            * include/bits/stl_algo.h (__rotate): Use unsigned values for
            division.

Diff:
---
 libstdc++-v3/include/bits/stl_algo.h | 10 ++++++++--
 1 file changed, 8 insertions(+), 2 deletions(-)

diff --git a/libstdc++-v3/include/bits/stl_algo.h b/libstdc++-v3/include/bits/stl_algo.h
index 9496b53f8871..7a0cf6b67370 100644
--- a/libstdc++-v3/include/bits/stl_algo.h
+++ b/libstdc++-v3/include/bits/stl_algo.h
@@ -1251,6 +1251,12 @@ _GLIBCXX_BEGIN_INLINE_ABI_NAMESPACE(_V2)
       typedef typename iterator_traits<_RandomAccessIterator>::value_type
 	_ValueType;
 
+#if __cplusplus >= 201103L
+      typedef typename make_unsigned<_Distance>::type _UDistance;
+#else
+      typedef _Distance _UDistance;
+#endif
+
       _Distance __n = __last   - __first;
       _Distance __k = __middle - __first;
 
@@ -1281,7 +1287,7 @@ _GLIBCXX_BEGIN_INLINE_ABI_NAMESPACE(_V2)
 		  ++__p;
 		  ++__q;
 		}
-	      __n %= __k;
+	      __n = static_cast<_UDistance>(__n) % static_cast<_UDistance>(__k);
 	      if (__n == 0)
 		return __ret;
 	      std::swap(__n, __k);
@@ -1305,7 +1311,7 @@ _GLIBCXX_BEGIN_INLINE_ABI_NAMESPACE(_V2)
 		  --__q;
 		  std::iter_swap(__p, __q);
 		}
-	      __n %= __k;
+	      __n = static_cast<_UDistance>(__n) % static_cast<_UDistance>(__k);
 	      if (__n == 0)
 		return __ret;
 	      std::swap(__n, __k);