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[libc++][NFC] Reuse __bit_log2 for sort #135303

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Merged
merged 4 commits into from
Apr 13, 2025
Merged

[libc++][NFC] Reuse __bit_log2 for sort #135303

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8312140
[libc++][NFC] Reuse `__bit_log2` for `sort`
frederick-vs-ja Apr 11, 2025
817b7aa
Merge branch 'main' into sort-with-bit-log2
frederick-vs-ja Apr 11, 2025
dd930d7
Adopt @philnik777's review comments
frederick-vs-ja Apr 11, 2025
6246433
Merge branch 'main' into sort-with-bit-log2
frederick-vs-ja Apr 12, 2025
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24 changes: 4 additions & 20 deletions libcxx/include/__algorithm/sort.h
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Original file line number Diff line number Diff line change
Expand Up @@ -17,6 +17,7 @@
#include <__algorithm/partial_sort.h>
#include <__algorithm/unwrap_iter.h>
#include <__assert>
#include <__bit/bit_log2.h>
#include <__bit/blsr.h>
#include <__bit/countl.h>
#include <__bit/countr.h>
Expand All @@ -34,6 +35,7 @@
#include <__type_traits/is_constant_evaluated.h>
#include <__type_traits/is_same.h>
#include <__type_traits/is_trivially_copyable.h>
#include <__type_traits/make_unsigned.h>
#include <__utility/move.h>
#include <__utility/pair.h>
#include <climits>
Expand Down Expand Up @@ -826,25 +828,6 @@ void __introsort(_RandomAccessIterator __first,
}
}

template <typename _Number>
inline _LIBCPP_HIDE_FROM_ABI _Number __log2i(_Number __n) {
if (__n == 0)
return 0;
if (sizeof(__n) <= sizeof(unsigned))
return sizeof(unsigned) * CHAR_BIT - 1 - __libcpp_clz(static_cast<unsigned>(__n));
if (sizeof(__n) <= sizeof(unsigned long))
return sizeof(unsigned long) * CHAR_BIT - 1 - __libcpp_clz(static_cast<unsigned long>(__n));
if (sizeof(__n) <= sizeof(unsigned long long))
return sizeof(unsigned long long) * CHAR_BIT - 1 - __libcpp_clz(static_cast<unsigned long long>(__n));

_Number __log2 = 0;
while (__n > 1) {
__log2++;
__n >>= 1;
}
return __log2;
}

template <class _Comp, class _RandomAccessIterator>
void __sort(_RandomAccessIterator, _RandomAccessIterator, _Comp);

Expand Down Expand Up @@ -878,7 +861,8 @@ template <class _AlgPolicy, class _RandomAccessIterator, class _Comp>
_LIBCPP_HIDE_FROM_ABI _LIBCPP_CONSTEXPR_SINCE_CXX20 void
__sort_dispatch(_RandomAccessIterator __first, _RandomAccessIterator __last, _Comp& __comp) {
typedef typename iterator_traits<_RandomAccessIterator>::difference_type difference_type;
difference_type __depth_limit = 2 * std::__log2i(__last - __first);
difference_type __depth_limit = static_cast<difference_type>(
2 * std::__bit_log2(static_cast<__make_unsigned_t<difference_type> >(__last - __first)));

// Only use bitset partitioning for arithmetic types. We should also check
// that the default comparator is in use so that we are sure that there are no
Expand Down
6 changes: 1 addition & 5 deletions libcxx/include/__bit/bit_log2.h
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Original file line number Diff line number Diff line change
Expand Up @@ -20,16 +20,12 @@

_LIBCPP_BEGIN_NAMESPACE_STD

#if _LIBCPP_STD_VER >= 14

template <class _Tp>
_LIBCPP_HIDE_FROM_ABI constexpr _Tp __bit_log2(_Tp __t) noexcept {
_LIBCPP_HIDE_FROM_ABI _LIBCPP_CONSTEXPR_SINCE_CXX14 _Tp __bit_log2(_Tp __t) _NOEXCEPT {
static_assert(__libcpp_is_unsigned_integer<_Tp>::value, "__bit_log2 requires an unsigned integer type");
return numeric_limits<_Tp>::digits - 1 - std::__countl_zero(__t);
}

#endif // _LIBCPP_STD_VER >= 14

_LIBCPP_END_NAMESPACE_STD

#endif // _LIBCPP___BIT_BIT_LOG2_H
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