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Revert "Bug 39129: Speeding up partition_point/lower_bound/upper_bound/ by using unsigned division by 2 when possible."

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This reverts r345525. I'm reverting because that patch apparently caused
a regression on certain platforms (see https://reviews.llvm.org/D53994).
Since we don't fully understand the reasons for the regression, I'm
reverting until we can provide a fix we understand.

git-svn-id: https://llvm.org/svn/llvm-project/libcxx/trunk@345893 91177308-0d34-0410-b5e6-96231b3b80d8
This commit is contained in:
Louis Dionne
2018-11-01 21:24:32 +00:00
parent 6115b72f60
commit 5dc37768e2
3 changed files with 4 additions and 153 deletions
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34
include/algorithm
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@@ -750,32 +750,6 @@ public:
bool operator()(const _T1& __x, const _T2& __y) {return __p_(__y, __x);}
};
// Perform division by two quickly for positive integers (llvm.org/PR39129)
template <typename _Integral>
_LIBCPP_INLINE_VISIBILITY _LIBCPP_CONSTEXPR
typename enable_if
<
is_integral<_Integral>::value,
_Integral
>::type
__half_positive(_Integral __value)
{
return static_cast<_Integral>(static_cast<typename make_unsigned<_Integral>::type>(__value) / 2);
}
template <typename _Tp>
_LIBCPP_INLINE_VISIBILITY _LIBCPP_CONSTEXPR
typename enable_if
<
!is_integral<_Tp>::value,
_Tp
>::type
__half_positive(_Tp __value)
{
return __value / 2;
}
#ifdef _LIBCPP_DEBUG
template <class _Compare>
@@ -3228,7 +3202,7 @@ partition_point(_ForwardIterator __first, _ForwardIterator __last, _Predicate __
difference_type __len = _VSTD::distance(__first, __last);
while (__len != 0)
{
difference_type __l2 = _VSTD::__half_positive(__len);
difference_type __l2 = __len / 2;
_ForwardIterator __m = __first;
_VSTD::advance(__m, __l2);
if (__pred(*__m))
@@ -4095,7 +4069,7 @@ __lower_bound(_ForwardIterator __first, _ForwardIterator __last, const _Tp& __va
difference_type __len = _VSTD::distance(__first, __last);
while (__len != 0)
{
difference_type __l2 = _VSTD::__half_positive(__len);
difference_type __l2 = __len / 2;
_ForwardIterator __m = __first;
_VSTD::advance(__m, __l2);
if (__comp(*__m, __value_))
@@ -4137,7 +4111,7 @@ __upper_bound(_ForwardIterator __first, _ForwardIterator __last, const _Tp& __va
difference_type __len = _VSTD::distance(__first, __last);
while (__len != 0)
{
difference_type __l2 = _VSTD::__half_positive(__len);
difference_type __l2 = __len / 2;
_ForwardIterator __m = __first;
_VSTD::advance(__m, __l2);
if (__comp(__value_, *__m))
@@ -4179,7 +4153,7 @@ __equal_range(_ForwardIterator __first, _ForwardIterator __last, const _Tp& __va
difference_type __len = _VSTD::distance(__first, __last);
while (__len != 0)
{
difference_type __l2 = _VSTD::__half_positive(__len);
difference_type __l2 = __len / 2;
_ForwardIterator __m = __first;
_VSTD::advance(__m, __l2);
if (__comp(*__m, __value_))