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// -*- C++ -*-
// -*-===----------------------------------------------------------------------===//
//
// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
//
// Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
// See https://llvm.org/LICENSE.txt for license information.
//
//===----------------------------------------------------------------------===//
#ifndef _PSTL_INTERNAL_OMP_PARALLEL_REDUCE_H
#define _PSTL_INTERNAL_OMP_PARALLEL_REDUCE_H
#include "util.h"
namespace __pstl
{
namespace __omp_backend
{
template <class _RandomAccessIterator, class _Value, typename _RealBody, typename _Reduction>
_Value
__parallel_reduce_body(_RandomAccessIterator __first, _RandomAccessIterator __last, _Value __identity,
_RealBody __real_body, _Reduction __reduce)
{
if (__should_run_serial(__first, __last))
{
return __real_body(__first, __last, __identity);
}
auto __middle = __first + ((__last - __first) / 2);
_Value __v1(__identity), __v2(__identity);
__parallel_invoke_body(
[&]() { __v1 = __parallel_reduce_body(__first, __middle, __identity, __real_body, __reduce); },
[&]() { __v2 = __parallel_reduce_body(__middle, __last, __identity, __real_body, __reduce); });
return __reduce(__v1, __v2);
}
//------------------------------------------------------------------------
// Notation:
// r(i,j,init) returns reduction of init with reduction over [i,j)
// c(x,y) combines values x and y that were the result of r
//------------------------------------------------------------------------
template <class _ExecutionPolicy, class _RandomAccessIterator, class _Value, typename _RealBody, typename _Reduction>
_Value
__parallel_reduce(__pstl::__internal::__openmp_backend_tag, _ExecutionPolicy&&, _RandomAccessIterator __first,
_RandomAccessIterator __last, _Value __identity, _RealBody __real_body, _Reduction __reduction)
{
// We don't create a nested parallel region in an existing parallel region:
// just create tasks.
if (omp_in_parallel())
{
return __pstl::__omp_backend::__parallel_reduce_body(__first, __last, __identity, __real_body, __reduction);
}
// In any case (nested or non-nested) one parallel region is created and only
// one thread creates a set of tasks.
_Value __res = __identity;
_PSTL_PRAGMA(omp parallel)
_PSTL_PRAGMA(omp single nowait)
{
__res = __pstl::__omp_backend::__parallel_reduce_body(__first, __last, __identity, __real_body, __reduction);
}
return __res;
}
} // namespace __omp_backend
} // namespace __pstl
#endif // _PSTL_INTERNAL_OMP_PARALLEL_REDUCE_H
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