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Take advantage of random access iterators in the source range to avoid bounds checking on segmented iterators

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This commit is contained in:
Ion Gaztañaga
2026-05-05 14:08:52 +02:00
parent ce2bbf6f67
commit 562707ff8b
1 changed files with 41 additions and 40 deletions
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include/boost/container/experimental/segmented_copy_n.hpp
+41 -40
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@@ -49,7 +49,7 @@ namespace detail_algo {
template <class SrcIter, class SrcSent, class Size, class DstIter, class DstSent>
BOOST_CONTAINER_FORCEINLINE
segduo<SrcIter, DstIter> segmented_copy_n_src_dst_bounded
(SrcIter first, SrcSent last, Size& count, DstIter dst_first, DstSent dst_last)
(SrcIter first, SrcSent last, Size& BOOST_RESTRICT count, DstIter dst_first, DstSent dst_last)
{
while(count >= Size(4)) {
if(dst_first == dst_last || first == last) goto out_path;
@@ -87,7 +87,7 @@ segduo<SrcIter, DstIter> segmented_copy_n_src_dst_bounded
template <class SrcIter, class SrcSent, class Size, class DstIter, class DstSent>
BOOST_CONTAINER_FORCEINLINE segduo<SrcIter, DstIter>
segmented_copy_n_src_dst_bounded
(SrcIter first, SrcSent last, Size& count, DstIter dst_first, DstSent dst_last)
(SrcIter first, SrcSent last, Size& BOOST_RESTRICT count, DstIter dst_first, DstSent dst_last)
{
for(; count > 0; ++first, --count) {
if(dst_first == dst_last || first == last)
@@ -107,10 +107,10 @@ BOOST_CONTAINER_FORCEINLINE
typename iterator_disable_if_tag
<DstIter, std::random_access_iterator_tag, segduo<SrcIter, DstIter> >::type
#else
segduo<SrcIter, DstIter>
segduo<SrcIter, DstIter>
#endif
segmented_copy_n_dst_bounded
(SrcIter first, SrcSent last, Size& count, DstIter dst_first, DstSent dst_last, const non_segmented_iterator_tag &)
(SrcIter first, SrcSent last, Size& BOOST_RESTRICT count, DstIter dst_first, DstSent dst_last, const non_segmented_iterator_tag &)
{
return (segmented_copy_n_src_dst_bounded)(first, last, count, dst_first, dst_last);
}
@@ -122,7 +122,7 @@ BOOST_CONTAINER_FORCEINLINE
typename iterator_enable_if_tag
<RADstIter, std::random_access_iterator_tag, segduo<RASrcIter, RADstIter> >::type
segmented_copy_n_dst_bounded
(RASrcIter first, SrcSent last, Size& count, RADstIter dst_first, RADstIter dst_last, const non_segmented_iterator_tag &)
(RASrcIter first, SrcSent last, Size& BOOST_RESTRICT count, RADstIter dst_first, RADstIter dst_last, const non_segmented_iterator_tag &)
{
typedef typename iterator_traits<RADstIter>::difference_type difference_type;
const difference_type dst_n = dst_last - dst_first;
@@ -141,7 +141,7 @@ segmented_copy_n_dst_bounded
template <class SrcIter, class SrcSent, class Size, class SegDstIter>
segduo<SrcIter, SegDstIter> segmented_copy_n_dst_bounded
(SrcIter first, SrcSent last, Size& count, SegDstIter dst_first, SegDstIter dst_last, const segmented_iterator_tag &)
(SrcIter first, SrcSent last, Size& BOOST_RESTRICT count, SegDstIter dst_first, SegDstIter dst_last, const segmented_iterator_tag &)
{
typedef segmented_iterator_traits<SegDstIter> dst_traits;
typedef typename dst_traits::local_iterator dst_local_iterator;
@@ -185,7 +185,7 @@ segduo<SrcIter, SegDstIter> segmented_copy_n_dst_bounded
template <class SrcIter, class SrcSent, class Size, class DstIter>
BOOST_CONTAINER_FORCEINLINE DstIter segmented_copy_n_dst_dispatch
(SrcIter first, SrcSent last, Size& count, DstIter result, const non_segmented_iterator_tag &)
(SrcIter first, SrcSent last, Size& BOOST_RESTRICT count, DstIter result, const non_segmented_iterator_tag &)
{
return (segmented_copy_n_src_dst_bounded)
(first, last, count, result, unreachable_sentinel_t()).second;
@@ -193,7 +193,7 @@ BOOST_CONTAINER_FORCEINLINE DstIter segmented_copy_n_dst_dispatch
template <class SrcIter, class SrcSent, class Size, class SegDstIter>
SegDstIter segmented_copy_n_dst_dispatch
(SrcIter first, SrcSent last, Size& count, SegDstIter result, const segmented_iterator_tag &)
(SrcIter first, SrcSent last, Size& BOOST_RESTRICT count, SegDstIter result, const segmented_iterator_tag &)
{
typedef segmented_iterator_traits<SegDstIter> dst_traits;
typedef typename dst_traits::local_iterator dst_local_iterator;
@@ -207,9 +207,8 @@ SegDstIter segmented_copy_n_dst_dispatch
dst_local_iterator dst_local = dst_traits::local(result);
while(1) {
const dst_local_iterator dst_end = dst_traits::end(dst_seg);
const segduo<SrcIter, dst_local_iterator> r = (segmented_copy_n_dst_bounded)
(first, last, count, dst_local, dst_end, dst_is_local_seg_t());
(first, last, count, dst_local, dst_traits::end(dst_seg), dst_is_local_seg_t());
first = r.first;
//Exit when count is satisfied or the source range is exhausted.
//The src-exhaustion check matters when this routine is invoked with
@@ -229,27 +228,27 @@ SegDstIter segmented_copy_n_dst_dispatch
template <class InIter, class Size, class OutIter>
BOOST_CONTAINER_FORCEINLINE
OutIter copy_n_scan_non_segmented
(InIter first, InIter last, Size& count, OutIter result, const std::random_access_iterator_tag &)
OutIter copy_n_scan
( InIter first, InIter last, Size& BOOST_RESTRICT count
, OutIter result, non_segmented_iterator_tag, const std::random_access_iterator_tag &)
{
Size range_sz = Size(last - first);
const Size range_sz = Size(last - first);
Size min_count = count <= range_sz ? count : range_sz;
count -= min_count;
return segmented_copy_n_src_dst_bounded
(first, unreachable_sentinel_t(), min_count, result, unreachable_sentinel_t()).second;
#if !defined(BOOST_CONTAINER_DISABLE_MULTI_SEGMENTED_ALGO)
typedef segmented_iterator_traits<OutIter> dst_traits;
return (segmented_copy_n_dst_dispatch)
(first, unreachable_sentinel_t(), min_count, result, typename dst_traits::is_segmented_iterator());
#else
return (segmented_copy_n_src_dst_bounded)
(first, unreachable_sentinel_t(), min_count, result, unreachable_sentinel_t()).second;
#endif
}
template <class InIter, class Size, class OutIter, class Tag>
template <class InIter, class Size, class OutIter, class Cat>
BOOST_CONTAINER_FORCEINLINE
OutIter copy_n_scan_non_segmented(InIter first, InIter last, Size& count, OutIter result, Tag)
{
return segmented_copy_n_src_dst_bounded
(first, last, count, result, unreachable_sentinel_t()).second;
}
template <class InIter, class Size, class OutIter>
BOOST_CONTAINER_FORCEINLINE
OutIter copy_n_scan(InIter first, InIter last, Size& count, OutIter result, non_segmented_iterator_tag)
OutIter copy_n_scan
(InIter first, InIter last, Size& BOOST_RESTRICT count, OutIter result, non_segmented_iterator_tag, const Cat &)
{
#if !defined(BOOST_CONTAINER_DISABLE_MULTI_SEGMENTED_ALGO)
typedef segmented_iterator_traits<OutIter> dst_traits;
@@ -261,34 +260,35 @@ OutIter copy_n_scan(InIter first, InIter last, Size& count, OutIter result, non_
#endif
}
template <class SegIt, class Size, class OutIter>
OutIter copy_n_scan(SegIt first, SegIt last, Size& count, OutIter result, segmented_iterator_tag)
template <class SegIt, class Size, class OutIter, class Cat>
OutIter copy_n_scan(SegIt first, SegIt last, Size& BOOST_RESTRICT count, OutIter result, segmented_iterator_tag, const Cat &)
{
typedef segmented_iterator_traits<SegIt> traits;
typedef typename traits::local_iterator local_iterator;
typedef typename traits::segment_iterator segment_iterator;
typedef typename segmented_iterator_traits<local_iterator>::is_segmented_iterator is_local_seg_t;
typedef segmented_iterator_traits<SegIt> traits;
typedef typename traits::local_iterator local_iterator;
typedef typename traits::segment_iterator segment_iterator;
typedef typename segmented_iterator_traits<local_iterator>::is_segmented_iterator is_local_seg_t;
typedef typename iterator_traits<local_iterator>::iterator_category local_cat_t;
segment_iterator scur = traits::segment(first);
segment_iterator slast = traits::segment(last);
local_iterator lcur = traits::local(first);
if(scur == slast) {
return copy_n_scan(lcur, traits::local(last), count, result, is_local_seg_t());
return copy_n_scan(lcur, traits::local(last), count, result, is_local_seg_t(), local_cat_t());
}
else {
result = copy_n_scan(lcur, traits::end(scur), count, result, is_local_seg_t());
result = copy_n_scan(lcur, traits::end(scur), count, result, is_local_seg_t(), local_cat_t());
if (!count)
return result;
for (++scur; scur != slast; ++scur) {
result = copy_n_scan(traits::begin(scur), traits::end(scur), count, result, is_local_seg_t());
result = copy_n_scan(traits::begin(scur), traits::end(scur), count, result, is_local_seg_t(), local_cat_t());
if (!count)
return result;
}
return copy_n_scan(traits::begin(scur), traits::local(last), count, result, is_local_seg_t());
return copy_n_scan(traits::begin(scur), traits::local(last), count, result, is_local_seg_t(), local_cat_t());
}
}
@@ -298,12 +298,13 @@ OutIter copy_n_scan(SegIt first, SegIt last, Size& count, OutIter result, segmen
template <class SegIter, class Size, class OutIter, class Cat>
OutIter segmented_copy_n_dispatch
(SegIter first, Size count, OutIter result, segmented_iterator_tag, Cat)
(SegIter first, Size count, OutIter result, const segmented_iterator_tag &, Cat)
{
typedef segmented_iterator_traits<SegIter> traits;
typedef typename traits::local_iterator local_iterator;
typedef typename traits::segment_iterator segment_iterator;
typedef typename segmented_iterator_traits<local_iterator>::is_segmented_iterator is_local_seg_t;
typedef typename iterator_traits<local_iterator>::iterator_category local_cat_t;
if(count <= 0) return result;
@@ -311,7 +312,7 @@ OutIter segmented_copy_n_dispatch
local_iterator lcur = traits::local(first);
while(1) {
result = copy_n_scan(lcur, traits::end(scur), count, result, is_local_seg_t());
result = copy_n_scan(lcur, traits::end(scur), count, result, is_local_seg_t(), local_cat_t());
if(count == 0)
break;
@@ -323,15 +324,15 @@ OutIter segmented_copy_n_dispatch
template <class InIter, class Size, class OutIter, class Cat>
BOOST_CONTAINER_FORCEINLINE OutIter segmented_copy_n_dispatch
(InIter first, Size count, OutIter result, non_segmented_iterator_tag, Cat)
(InIter first, Size count, OutIter result, const non_segmented_iterator_tag &, const Cat&)
{
#if !defined(BOOST_CONTAINER_DISABLE_MULTI_SEGMENTED_ALGO)
typedef segmented_iterator_traits<OutIter> dst_traits;
return (segmented_copy_n_dst_dispatch)
(first, unreachable_sentinel_t(), count, result, typename dst_traits::is_segmented_iterator());
#else
return (segmented_copy_n_dst_dispatch)
(first, unreachable_sentinel_t(), count, result, non_segmented_iterator_tag());
return (segmented_copy_n_src_dst_bounded)
(first, unreachable_sentinel_t(), count, result, unreachable_sentinel_t()).second;
#endif
}