LineageOS/android_external_libcxx
1
0
Fork 0
Code Issues Pull Requests Packages Projects Releases Wiki Activity

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

Browse Source 
Patch by Denis Yaroshevskiy (denis.yaroshevskij@gmail.com)

The rational and measurements can be found in the bug description: https://bugs.llvm.org/show_bug.cgi?id=39129

Reviewed as https://reviews.llvm.org/D52697


git-svn-id: https://llvm.org/svn/llvm-project/libcxx/trunk@345525 91177308-0d34-0410-b5e6-96231b3b80d8
This commit is contained in:
Eric Fiselier
2018-10-29 19:25:02 +00:00
parent 081dda5c16
commit 207b919735
3 changed files with 153 additions and 4 deletions
Download Patch File Download Diff File Expand all files Collapse all files

34
include/algorithm
View File

@@ -750,6 +750,32 @@ 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>
@@ -3202,7 +3228,7 @@ partition_point(_ForwardIterator __first, _ForwardIterator __last, _Predicate __
difference_type __len = _VSTD::distance(__first, __last);
while (__len != 0)
{
difference_type __l2 = __len / 2;
difference_type __l2 = _VSTD::__half_positive(__len);
_ForwardIterator __m = __first;
_VSTD::advance(__m, __l2);
if (__pred(*__m))
@@ -4069,7 +4095,7 @@ __lower_bound(_ForwardIterator __first, _ForwardIterator __last, const _Tp& __va
difference_type __len = _VSTD::distance(__first, __last);
while (__len != 0)
{
difference_type __l2 = __len / 2;
difference_type __l2 = _VSTD::__half_positive(__len);
_ForwardIterator __m = __first;
_VSTD::advance(__m, __l2);
if (__comp(*__m, __value_))
@@ -4111,7 +4137,7 @@ __upper_bound(_ForwardIterator __first, _ForwardIterator __last, const _Tp& __va
difference_type __len = _VSTD::distance(__first, __last);
while (__len != 0)
{
difference_type __l2 = __len / 2;
difference_type __l2 = _VSTD::__half_positive(__len);
_ForwardIterator __m = __first;
_VSTD::advance(__m, __l2);
if (__comp(__value_, *__m))
@@ -4153,7 +4179,7 @@ __equal_range(_ForwardIterator __first, _ForwardIterator __last, const _Tp& __va
difference_type __len = _VSTD::distance(__first, __last);
while (__len != 0)
{
difference_type __l2 = __len / 2;
difference_type __l2 = _VSTD::__half_positive(__len);
_ForwardIterator __m = __first;
_VSTD::advance(__m, __l2);
if (__comp(*__m, __value_))