gcc/libstdc++-v3/include/pstl/numeric_impl.h

// -*- C++ -*-
//===-- numeric_impl.h ----------------------------------------------------===//
//
// Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
// See https://llvm.org/LICENSE.txt for license information.
// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
//
//===----------------------------------------------------------------------===//

#ifndef _PSTL_NUMERIC_IMPL_H
#define _PSTL_NUMERIC_IMPL_H

#include <iterator>
#include <type_traits>
#include <numeric>

#include "parallel_backend.h"
#include "pstl_config.h"
#include "execution_impl.h"
#include "unseq_backend_simd.h"
#include "algorithm_fwd.h"

namespace __pstl
{
namespace __internal
{

//------------------------------------------------------------------------
// transform_reduce (version with two binary functions, according to draft N4659)
//------------------------------------------------------------------------

template <class _ForwardIterator1, class _ForwardIterator2, class _Tp, class _BinaryOperation1, class _BinaryOperation2>
_Tp
__brick_transform_reduce(_ForwardIterator1 __first1, _ForwardIterator1 __last1, _ForwardIterator2 __first2, _Tp __init,
                         _BinaryOperation1 __binary_op1, _BinaryOperation2 __binary_op2,
                         /*is_vector=*/std::false_type) noexcept
{
    return std::inner_product(__first1, __last1, __first2, __init, __binary_op1, __binary_op2);
}

template <class _RandomAccessIterator1, class _RandomAccessIterator2, class _Tp, class _BinaryOperation1,
          class _BinaryOperation2>
_Tp
__brick_transform_reduce(_RandomAccessIterator1 __first1, _RandomAccessIterator1 __last1,
                         _RandomAccessIterator2 __first2, _Tp __init, _BinaryOperation1 __binary_op1,
                         _BinaryOperation2 __binary_op2,
                         /*is_vector=*/std::true_type) noexcept
{
    typedef typename std::iterator_traits<_RandomAccessIterator1>::difference_type _DifferenceType;
    return __unseq_backend::__simd_transform_reduce(
        __last1 - __first1, __init, __binary_op1,
        [=, &__binary_op2](_DifferenceType __i) { return __binary_op2(__first1[__i], __first2[__i]); });
}

template <class _Tag, class _ExecutionPolicy, class _ForwardIterator1, class _ForwardIterator2, class _Tp,
          class _BinaryOperation1, class _BinaryOperation2>
_Tp
__pattern_transform_reduce(_Tag, _ExecutionPolicy&&, _ForwardIterator1 __first1, _ForwardIterator1 __last1,
                           _ForwardIterator2 __first2, _Tp __init, _BinaryOperation1 __binary_op1,
                           _BinaryOperation2 __binary_op2) noexcept
{
    return __brick_transform_reduce(__first1, __last1, __first2, __init, __binary_op1, __binary_op2,
                                    typename _Tag::__is_vector{});
}

template <class _IsVector, class _ExecutionPolicy, class _RandomAccessIterator1, class _RandomAccessIterator2,
          class _Tp, class _BinaryOperation1, class _BinaryOperation2>
_Tp
__pattern_transform_reduce(__parallel_tag<_IsVector> __tag, _ExecutionPolicy&& __exec, _RandomAccessIterator1 __first1,
                           _RandomAccessIterator1 __last1, _RandomAccessIterator2 __first2, _Tp __init,
                           _BinaryOperation1 __binary_op1, _BinaryOperation2 __binary_op2)
{
    using __backend_tag = typename decltype(__tag)::__backend_tag;

    return __internal::__except_handler(
        [&]()
        {
            return __par_backend::__parallel_transform_reduce(
                __backend_tag{}, std::forward<_ExecutionPolicy>(__exec), __first1, __last1,
                [__first1, __first2, __binary_op2](_RandomAccessIterator1 __i) mutable
                { return __binary_op2(*__i, *(__first2 + (__i - __first1))); },
                __init,
                __binary_op1, // Combine
                [__first1, __first2, __binary_op1, __binary_op2](_RandomAccessIterator1 __i, _RandomAccessIterator1 __j,
                                                                 _Tp __init) -> _Tp
                {
                    return __internal::__brick_transform_reduce(__i, __j, __first2 + (__i - __first1), __init,
                                                                __binary_op1, __binary_op2, _IsVector{});
                });
        });
}

//------------------------------------------------------------------------
// transform_reduce (version with unary and binary functions)
//------------------------------------------------------------------------

template <class _ForwardIterator, class _Tp, class _BinaryOperation, class _UnaryOperation>
_Tp
__brick_transform_reduce(_ForwardIterator __first, _ForwardIterator __last, _Tp __init, _BinaryOperation __binary_op,
                         _UnaryOperation __unary_op, /*is_vector=*/std::false_type) noexcept
{
    return std::transform_reduce(__first, __last, __init, __binary_op, __unary_op);
}

template <class _RandomAccessIterator, class _Tp, class _UnaryOperation, class _BinaryOperation>
_Tp
__brick_transform_reduce(_RandomAccessIterator __first, _RandomAccessIterator __last, _Tp __init,
                         _BinaryOperation __binary_op, _UnaryOperation __unary_op,
                         /*is_vector=*/std::true_type) noexcept
{
    typedef typename std::iterator_traits<_RandomAccessIterator>::difference_type _DifferenceType;
    return __unseq_backend::__simd_transform_reduce(
        __last - __first, __init, __binary_op,
        [=, &__unary_op](_DifferenceType __i) { return __unary_op(__first[__i]); });
}

template <class _Tag, class _ExecutionPolicy, class _ForwardIterator, class _Tp, class _BinaryOperation,
          class _UnaryOperation>
_Tp
__pattern_transform_reduce(_Tag, _ExecutionPolicy&&, _ForwardIterator __first, _ForwardIterator __last, _Tp __init,
                           _BinaryOperation __binary_op, _UnaryOperation __unary_op) noexcept
{
    return __internal::__brick_transform_reduce(__first, __last, __init, __binary_op, __unary_op,
                                                typename _Tag::__is_vector{});
}

template <class _IsVector, class _ExecutionPolicy, class _RandomAccessIterator, class _Tp, class _BinaryOperation,
          class _UnaryOperation>
_Tp
__pattern_transform_reduce(__parallel_tag<_IsVector> __tag, _ExecutionPolicy&& __exec, _RandomAccessIterator __first,
                           _RandomAccessIterator __last, _Tp __init, _BinaryOperation __binary_op,
                           _UnaryOperation __unary_op)
{
    using __backend_tag = typename decltype(__tag)::__backend_tag;

    return __internal::__except_handler(
        [&]()
        {
            return __par_backend::__parallel_transform_reduce(
                __backend_tag{}, std::forward<_ExecutionPolicy>(__exec), __first, __last,
                [__unary_op](_RandomAccessIterator __i) mutable { return __unary_op(*__i); }, __init, __binary_op,
                [__unary_op, __binary_op](_RandomAccessIterator __i, _RandomAccessIterator __j, _Tp __init) {
                    return __internal::__brick_transform_reduce(__i, __j, __init, __binary_op, __unary_op, _IsVector{});
                });
        });
}

//------------------------------------------------------------------------
// transform_exclusive_scan
//
// walk3 evaluates f(x,y,z) for (x,y,z) drawn from [first1,last1), [first2,...), [first3,...)
//------------------------------------------------------------------------

// Exclusive form
template <class _ForwardIterator, class _OutputIterator, class _UnaryOperation, class _Tp, class _BinaryOperation>
std::pair<_OutputIterator, _Tp>
__brick_transform_scan(_ForwardIterator __first, _ForwardIterator __last, _OutputIterator __result,
                       _UnaryOperation __unary_op, _Tp __init, _BinaryOperation __binary_op,
                       /*Inclusive*/ std::false_type, /*is_vector=*/std::false_type) noexcept
{
    for (; __first != __last; ++__first, ++__result)
    {
        *__result = __init;
        _PSTL_PRAGMA_FORCEINLINE
        __init = __binary_op(__init, __unary_op(*__first));
    }
    return std::make_pair(__result, __init);
}

// Inclusive form
template <class _RandomAccessIterator, class _OutputIterator, class _UnaryOperation, class _Tp, class _BinaryOperation>
std::pair<_OutputIterator, _Tp>
__brick_transform_scan(_RandomAccessIterator __first, _RandomAccessIterator __last, _OutputIterator __result,
                       _UnaryOperation __unary_op, _Tp __init, _BinaryOperation __binary_op,
                       /*Inclusive*/ std::true_type, /*is_vector=*/std::false_type) noexcept
{
    for (; __first != __last; ++__first, ++__result)
    {
        _PSTL_PRAGMA_FORCEINLINE
        __init = __binary_op(__init, __unary_op(*__first));
        *__result = __init;
    }
    return std::make_pair(__result, __init);
}

// type is arithmetic and binary operation is a user defined operation.
template <typename _Tp, typename _BinaryOperation>
using is_arithmetic_udop = std::integral_constant<bool, std::is_arithmetic<_Tp>::value &&
                                                            !std::is_same<_BinaryOperation, std::plus<_Tp>>::value>;

// [restriction] - T shall be DefaultConstructible.
// [violation] - default ctor of T shall set the identity value for binary_op.
template <class _RandomAccessIterator, class _OutputIterator, class _UnaryOperation, class _Tp, class _BinaryOperation,
          class _Inclusive>
typename std::enable_if<!is_arithmetic_udop<_Tp, _BinaryOperation>::value, std::pair<_OutputIterator, _Tp>>::type
__brick_transform_scan(_RandomAccessIterator __first, _RandomAccessIterator __last, _OutputIterator __result,
                       _UnaryOperation __unary_op, _Tp __init, _BinaryOperation __binary_op, _Inclusive,
                       /*is_vector=*/std::true_type) noexcept
{
#if defined(_PSTL_UDS_PRESENT)
    return __unseq_backend::__simd_scan(__first, __last - __first, __result, __unary_op, __init, __binary_op,
                                        _Inclusive());
#else
    // We need to call serial brick here to call function for inclusive and exclusive scan that depends on _Inclusive() value
    return __internal::__brick_transform_scan(__first, __last, __result, __unary_op, __init, __binary_op, _Inclusive(),
                                              /*is_vector=*/std::false_type());
#endif
}

template <class _RandomAccessIterator, class _OutputIterator, class _UnaryOperation, class _Tp, class _BinaryOperation,
          class _Inclusive>
typename std::enable_if<is_arithmetic_udop<_Tp, _BinaryOperation>::value, std::pair<_OutputIterator, _Tp>>::type
__brick_transform_scan(_RandomAccessIterator __first, _RandomAccessIterator __last, _OutputIterator __result,
                       _UnaryOperation __unary_op, _Tp __init, _BinaryOperation __binary_op, _Inclusive,
                       /*is_vector=*/std::true_type) noexcept
{
    return __internal::__brick_transform_scan(__first, __last, __result, __unary_op, __init, __binary_op, _Inclusive(),
                                              /*is_vector=*/std::false_type());
}

template <class _Tag, class _ExecutionPolicy, class _ForwardIterator, class _OutputIterator, class _UnaryOperation,
          class _Tp, class _BinaryOperation, class _Inclusive>
_OutputIterator
__pattern_transform_scan(_Tag, _ExecutionPolicy&&, _ForwardIterator __first, _ForwardIterator __last,
                         _OutputIterator __result, _UnaryOperation __unary_op, _Tp __init, _BinaryOperation __binary_op,
                         _Inclusive) noexcept
{
    return __internal::__brick_transform_scan(__first, __last, __result, __unary_op, __init, __binary_op, _Inclusive(),
                                              typename _Tag::__is_vector{})
        .first;
}

template <class _IsVector, class _ExecutionPolicy, class _RandomAccessIterator, class _OutputIterator,
          class _UnaryOperation, class _Tp, class _BinaryOperation, class _Inclusive>
typename std::enable_if<!std::is_floating_point<_Tp>::value, _OutputIterator>::type
__pattern_transform_scan(__parallel_tag<_IsVector> __tag, _ExecutionPolicy&& __exec, _RandomAccessIterator __first,
                         _RandomAccessIterator __last, _OutputIterator __result, _UnaryOperation __unary_op, _Tp __init,
                         _BinaryOperation __binary_op, _Inclusive)
{
    using __backend_tag = typename decltype(__tag)::__backend_tag;

    typedef typename std::iterator_traits<_RandomAccessIterator>::difference_type _DifferenceType;

    return __internal::__except_handler(
        [&]()
        {
            __par_backend::__parallel_transform_scan(
                __backend_tag{}, std::forward<_ExecutionPolicy>(__exec), __last - __first,
                [__first, __unary_op](_DifferenceType __i) mutable { return __unary_op(__first[__i]); }, __init,
                __binary_op,
                [__first, __unary_op, __binary_op](_DifferenceType __i, _DifferenceType __j, _Tp __init)
                {
                    // Execute serial __brick_transform_reduce, due to the explicit SIMD vectorization (reduction) requires a commutative operation for the guarantee of correct scan.
                    return __internal::__brick_transform_reduce(__first + __i, __first + __j, __init, __binary_op,
                                                                __unary_op,
                                                                /*__is_vector*/ std::false_type());
                },
                [__first, __unary_op, __binary_op, __result](_DifferenceType __i, _DifferenceType __j, _Tp __init)
                {
                    return __internal::__brick_transform_scan(__first + __i, __first + __j, __result + __i, __unary_op,
                                                              __init, __binary_op, _Inclusive(), _IsVector{})
                        .second;
                });
            return __result + (__last - __first);
        });
}

template <class _IsVector, class _ExecutionPolicy, class _RandomAccessIterator, class _OutputIterator,
          class _UnaryOperation, class _Tp, class _BinaryOperation, class _Inclusive>
typename std::enable_if<std::is_floating_point<_Tp>::value, _OutputIterator>::type
__pattern_transform_scan(__parallel_tag<_IsVector> __tag, _ExecutionPolicy&& __exec, _RandomAccessIterator __first,
                         _RandomAccessIterator __last, _OutputIterator __result, _UnaryOperation __unary_op, _Tp __init,
                         _BinaryOperation __binary_op, _Inclusive)
{
    using __backend_tag = typename decltype(__tag)::__backend_tag;

    typedef typename std::iterator_traits<_RandomAccessIterator>::difference_type _DifferenceType;
    _DifferenceType __n = __last - __first;

    if (__n <= 0)
    {
        return __result;
    }
    return __internal::__except_handler(
        [&]()
        {
            __par_backend::__parallel_strict_scan(
                __backend_tag{}, std::forward<_ExecutionPolicy>(__exec), __n, __init,
                [__first, __unary_op, __binary_op, __result](_DifferenceType __i, _DifferenceType __len)
                {
                    return __internal::__brick_transform_scan(__first + __i, __first + (__i + __len), __result + __i,
                                                              __unary_op, _Tp{}, __binary_op, _Inclusive(), _IsVector{})
                        .second;
                },
                __binary_op,
                [__result, &__binary_op](_DifferenceType __i, _DifferenceType __len, _Tp __initial)
                {
                    return *(std::transform(__result + __i, __result + __i + __len, __result + __i,
                                            [&__initial, &__binary_op](const _Tp& __x)
                                            {
                                                _PSTL_PRAGMA_FORCEINLINE
                                                return __binary_op(__initial, __x);
                                            }) -
                             1);
                },
                [](_Tp) {});
            return __result + (__last - __first);
        });
}

//------------------------------------------------------------------------
// adjacent_difference
//------------------------------------------------------------------------

template <class _ForwardIterator, class _OutputIterator, class _BinaryOperation>
_OutputIterator
__brick_adjacent_difference(_ForwardIterator __first, _ForwardIterator __last, _OutputIterator __d_first,
                            _BinaryOperation __op, /*is_vector*/ std::false_type) noexcept
{
    return std::adjacent_difference(__first, __last, __d_first, __op);
}

template <class _RandomAccessIterator1, class _RandomAccessIterator2, class _BinaryOperation>
_RandomAccessIterator2
__brick_adjacent_difference(_RandomAccessIterator1 __first, _RandomAccessIterator1 __last,
                            _RandomAccessIterator2 __d_first, _BinaryOperation __op,
                            /*is_vector=*/std::true_type) noexcept
{
    _PSTL_ASSERT(__first != __last);

    typedef typename std::iterator_traits<_RandomAccessIterator1>::reference _ReferenceType1;
    typedef typename std::iterator_traits<_RandomAccessIterator2>::reference _ReferenceType2;

    auto __n = __last - __first;
    *__d_first = *__first;
    return __unseq_backend::__simd_walk_3(
        __first + 1, __n - 1, __first, __d_first + 1,
        [&__op](_ReferenceType1 __x, _ReferenceType1 __y, _ReferenceType2 __z) { __z = __op(__x, __y); });
}

template <class _Tag, class _ExecutionPolicy, class _ForwardIterator, class _OutputIterator, class _BinaryOperation>
_OutputIterator
__pattern_adjacent_difference(_Tag, _ExecutionPolicy&&, _ForwardIterator __first, _ForwardIterator __last,
                              _OutputIterator __d_first, _BinaryOperation __op) noexcept
{
    return __internal::__brick_adjacent_difference(__first, __last, __d_first, __op, typename _Tag::__is_vector{});
}

template <class _IsVector, class _ExecutionPolicy, class _RandomAccessIterator1, class _RandomAccessIterator2,
          class _BinaryOperation>
_RandomAccessIterator2
__pattern_adjacent_difference(__parallel_tag<_IsVector> __tag, _ExecutionPolicy&& __exec,
                              _RandomAccessIterator1 __first, _RandomAccessIterator1 __last,
                              _RandomAccessIterator2 __d_first, _BinaryOperation __op)
{
    _PSTL_ASSERT(__first != __last);
    typedef typename std::iterator_traits<_RandomAccessIterator1>::reference _ReferenceType1;
    typedef typename std::iterator_traits<_RandomAccessIterator2>::reference _ReferenceType2;

    using __backend_tag = typename decltype(__tag)::__backend_tag;

    *__d_first = *__first;
    __par_backend::__parallel_for(__backend_tag{}, std::forward<_ExecutionPolicy>(__exec), __first, __last - 1,
                                  [&__op, __d_first, __first](_RandomAccessIterator1 __b, _RandomAccessIterator1 __e)
                                  {
                                      _RandomAccessIterator2 __d_b = __d_first + (__b - __first);
                                      __internal::__brick_walk3(
                                          __b, __e, __b + 1, __d_b + 1,
                                          [&__op](_ReferenceType1 __x, _ReferenceType1 __y, _ReferenceType2 __z)
                                          { __z = __op(__y, __x); },
                                          _IsVector{});
                                  });
    return __d_first + (__last - __first);
}

} // namespace __internal
} // namespace __pstl

#endif /* _PSTL_NUMERIC_IMPL_H */