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tuple: Make operator<() linear instead of exponential

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Patch by Matthew Dempsky!

git-svn-id: https://llvm.org/svn/llvm-project/libcxx/trunk@226641 91177308-0d34-0410-b5e6-96231b3b80d8
This commit is contained in:
Duncan P. N. Exon Smith 2015-01-21 02:51:17 +00:00
parent b3289a0c88
commit 07b133f2a7
1 changed files with 6 additions and 2 deletions

8
include/tuple

@ -927,8 +927,12 @@ struct __tuple_less
_LIBCPP_INLINE_VISIBILITY _LIBCPP_CONSTEXPR_AFTER_CXX11
bool operator()(const _Tp& __x, const _Up& __y)
{
return __tuple_less<_Ip-1>()(__x, __y) ||
(!__tuple_less<_Ip-1>()(__y, __x) && _VSTD::get<_Ip-1>(__x) < _VSTD::get<_Ip-1>(__y));
const size_t __idx = tuple_size<_Tp>::value - _Ip;
if (_VSTD::get<__idx>(__x) < _VSTD::get<__idx>(__y))
return true;
if (_VSTD::get<__idx>(__y) < _VSTD::get<__idx>(__x))
return false;
return __tuple_less<_Ip-1>()(__x, __y);
}
};