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//
// Redistribution and use in source and binary forms, with or without
// modification, are permitted provided that the following conditions
// are met:
// * Redistributions of source code must retain the above copyright
// notice, this list of conditions and the following disclaimer.
// * Redistributions in binary form must reproduce the above copyright
// notice, this list of conditions and the following disclaimer in the
// documentation and/or other materials provided with the distribution.
// * Neither the name of NVIDIA CORPORATION nor the names of its
// contributors may be used to endorse or promote products derived
// from this software without specific prior written permission.
//
// THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS ``AS IS'' AND ANY
// EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
// IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR
// PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT OWNER OR
// CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL,
// EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED TO,
// PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR
// PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY
// OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
// (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE
// OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
//
// Copyright (c) 2018 NVIDIA Corporation. All rights reserved.
#ifndef APEX_QUICK_SELECT_SMALLEST_K_H
#define APEX_QUICK_SELECT_SMALLEST_K_H
namespace nvidia
{
namespace apex
{
//A variant of quick sort to move the smallest k members of a sequence to its start.
//Does much less work than a full sort.
template<class Sortable, class Predicate>
PX_INLINE void ApexQuickSelectSmallestK(Sortable* start, Sortable* end, uint32_t k, const Predicate& p = Predicate())
{
Sortable* origStart = start;
Sortable* i;
Sortable* j;
Sortable m;
for (;;)
{
i = start;
j = end;
m = *(i + ((j - i) >> 1));
while (i <= j)
{
while (p(*i, m))
{
i++;
}
while (p(m, *j))
{
j--;
}
if (i <= j)
{
if (i != j)
{
nvidia::swap(*i, *j);
}
i++;
j--;
}
}
if (start < j
&& k + origStart - 1 < j) //we now have found the (j - start+1) smallest. we need to continue sorting these only if k < (j - start+1)
//if we sort this we definitely won't need to sort the right hand side.
{
end = j;
}
else if (i < end
&& k + origStart > i) //only continue sorting these if left side is not larger than k.
//we do this instead of recursing
{
start = i;
}
else
{
return;
}
}
}
} // namespace apex
} // namespace nvidia
#endif // APEX_QUICK_SELECT_SMALLEST_K_H
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