Implement parallel::unique_copy. #2754
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taeguk
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taeguk
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@taeguk: so is this ready to be reviewed now? |
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@hkaiser I'm ready to be reviewed. |
hpx/parallel/algorithms/unique.hpp
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| auto base_val = *first; | ||
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| *dest++ = *first; |
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You can't dereference input iterators more than once for the same 'position'.
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As I know, until input iterator is incremented, several dereferences are permitted.
GCC implementation : https://github.com/gcc-mirror/gcc/blob/master/libstdc%2B%2B-v3/include/bits/stl_algo.h#L1093-L1097
MSVC14 (VS2015) implementation :
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for (*_Dest++ = _Val; ++_First != _Last; )
if (!_Pred(_Val, *_First))
{ // copy unmatched
_Val = *_First;
*_Dest++ = _Val;
}
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Ok, I read the standard again - you're right. I'm not sure why I thought this to be undefined, I think I mixed it up with requirements for output iterators.
hpx/parallel/algorithms/unique.hpp
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| hpx::util::invoke(proj, *first))) | ||
| { | ||
| base_val = *first; | ||
| *dest++ = *first; |
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Same here, calling *first more than once without interleaving ++first is not allowed for input iterators. Not sure if this is worth changing as we know this will not be called with input iterators in the first place...
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policy.executor()instead ofhpx::launch::syncinscan_partitioner. (https://gist.github.com/taeguk/36f6fadce38c85096018f4df3a91d552)=> The parallel version is faster than the sequential version, but not satisfying.