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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.
This commit is contained in:
Jonathan Wakely 2024-02-08 15:40:32 +00:00
parent b58f0e5216
commit 4d819db7f2
1 changed files with 8 additions and 2 deletions
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10
libstdc++-v3/include/bits/stl_algo.h
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@ -1251,6 +1251,12 @@ _GLIBCXX_BEGIN_INLINE_ABI_NAMESPACE(_V2)
typedef typename iterator_traits<_RandomAccessIterator>::value_type typedef typename iterator_traits<_RandomAccessIterator>::value_type
_ValueType; _ValueType;
#if __cplusplus >= 201103L
typedef typename make_unsigned<_Distance>::type _UDistance;
#else
typedef _Distance _UDistance;
#endif
_Distance __n = __last - __first; _Distance __n = __last - __first;
_Distance __k = __middle - __first; _Distance __k = __middle - __first;
@ -1281,7 +1287,7 @@ _GLIBCXX_BEGIN_INLINE_ABI_NAMESPACE(_V2)
++__p; ++__p;
++__q; ++__q;
} }
__n %= __k; __n = static_cast<_UDistance>(__n) % static_cast<_UDistance>(__k);
if (__n == 0) if (__n == 0)
return __ret; return __ret;
std::swap(__n, __k); std::swap(__n, __k);
@ -1305,7 +1311,7 @@ _GLIBCXX_BEGIN_INLINE_ABI_NAMESPACE(_V2)
--__q; --__q;
std::iter_swap(__p, __q); std::iter_swap(__p, __q);
} }
__n %= __k; __n = static_cast<_UDistance>(__n) % static_cast<_UDistance>(__k);
if (__n == 0) if (__n == 0)
return __ret; return __ret;
std::swap(__n, __k); std::swap(__n, __k);