scan.h

/*
 * Copyright (c) 2014-2016, Siemens AG. All rights reserved.
 *
 * Redistribution and use in source and binary forms, with or without
 * modification, are permitted provided that the following conditions are met:
 *
 * 1. Redistributions of source code must retain the above copyright notice,
 * this list of conditions and the following disclaimer.
 *
 * 2. 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.
 *
 * THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS "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 HOLDER OR CONTRIBUTORS BE
 * LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR
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 * INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN
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 */

#ifndef EMBB_ALGORITHMS_SCAN_H_
#define EMBB_ALGORITHMS_SCAN_H_

#include <embb/mtapi/execution_policy.h>
#include <embb/algorithms/identity.h>

namespace embb {
namespace algorithms {

/**
 * \defgroup CPP_ALGORITHMS_SCAN Scan
 * Parallel scan computation
 * \ingroup CPP_ALGORITHMS
 *
 * \{
 */

#ifdef DOXYGEN

/**
 * Performs a parallel scan (or prefix) computation on a range of elements.
 *
 * The algorithm reads an input range and writes its result to a separate output
 * range. The input range consists of the elements from \c first to \c last,
 * excluding the last element. The output range consists of the elements from
 * \c output_first to <tt>output_first + std::difference(last - first)</tt>.
 *
 * The algorithm performs two runs on the given range. Hence, a performance
 * speedup can only be expected on processors with more than two cores.
 *
 * \throws embb::base::ErrorException if not enough MTAPI tasks can be created
 *         to satisfy the requirements of the algorithm.
 * \threadsafe if the elements in the range are not modified by another thread
 *             while the algorithm is executed.
 * \note No guarantee is given on the order in which the functions \c scan
 *       and \c transformation are applied to the elements.\n
 *       For all \c x of type \c ReturnType it must hold that
 *       <tt>reduction(x, neutral) == x</tt>. \n
 *       The reduction operation need not be commutative but must be
 *       associative, i.e., <tt>reduction(x, reduction(y, z)) ==
 *       reduction(reduction(x, y), z))</tt> for all \c x, \c y, \c z of type
 *       \c ReturnType.
 * \see embb::mtapi::ExecutionPolicy, Identity, ZipIterator
 * \tparam RAIIn Random access iterator type of input range
 * \tparam RAIOut Random access iterator type of output range
 * \tparam ReturnType Type of output elements of scan operation, deduced from
 *         \c neutral
 * \tparam ScanFunction Binary scan function object with signature
 *         <tt>ReturnType ScanFunction(ReturnType, ReturnType)</tt>
 * \tparam TransformationFunction Unary transformation function object with
 *         signature <tt>ReturnType TransformationFunction(typename
 *         std::iterator_traits<RAIIn>::value_type)</tt>.
 */
template<typename RAIIn, typename RAIOut, typename ReturnType,
         typename ScanFunction, typename TransformationFunction>
void Scan(
  RAIIn first,
  /**< [IN] Random access iterator pointing to the first element of the input
            range */
  RAIIn last,
  /**< [IN] Random access iterator pointing to the last plus one element of the
            input range */
  RAIOut output_first,
  /**< [IN] Random access iterator pointing to the first element of the output
            range */
  ReturnType neutral,
  /**< [IN] Neutral element of the \c scan operation. */
  ScanFunction scan,
  /**< [IN] Scan operation to be applied to the elements of the input range */
  TransformationFunction transformation = Identity(),
  /**< [IN] Transforms the elements of the input range before the scan operation
            is applied */
  const embb::mtapi::ExecutionPolicy& policy = embb::mtapi::ExecutionPolicy(),
  /**< [IN] embb::mtapi::ExecutionPolicy for the scan computation */
  size_t block_size = 0
  /**< [IN] Lower bound for partitioning the range of elements into blocks that
            are treated in parallel. Partitioning of a block stops if its size
            is less than or equal to \c block_size. The default value 0 means
            that the minimum block size is determined automatically depending on
            the number of elements in the range divided by the number of
            available cores. */
  );

#else // DOXYGEN

/**
 * Overload of above described Doxygen dummy.
 */
template<typename RAIIn, typename RAIOut, typename ReturnType,
         typename ScanFunction, typename TransformationFunction>
void Scan(
  RAIIn first,
  RAIIn last,
  RAIOut output_iterator,
  ReturnType neutral,
  ScanFunction scan,
  TransformationFunction transformation,
  const embb::mtapi::ExecutionPolicy& policy,
  size_t block_size
  );

/**
 * Overload of above described Doxygen dummy with less arguments.
 */
template<typename RAIIn, typename RAIOut, typename ReturnType,
         typename ScanFunction>
void Scan(
  RAIIn first,
  RAIIn last,
  RAIOut output_iterator,
  ReturnType neutral,
  ScanFunction scan
  ) {
  Scan(first, last, output_iterator, neutral, scan, Identity(),
    embb::mtapi::ExecutionPolicy(), 0);
}

/**
 * Overload of above described Doxygen dummy with less arguments.
 */
template<typename RAIIn, typename RAIOut, typename ReturnType,
         typename ScanFunction, typename TransformationFunction>
void Scan(
  RAIIn first,
  RAIIn last,
  RAIOut output_iterator,
  ReturnType neutral,
  ScanFunction scan,
  TransformationFunction transformation
  ) {
  Scan(first, last, output_iterator, neutral, scan, transformation,
    embb::mtapi::ExecutionPolicy(), 0);
}

/**
 * Overload of above described Doxygen dummy with less arguments.
 */
template<typename RAIIn, typename RAIOut, typename ReturnType,
         typename ScanFunction, typename TransformationFunction>
void Scan(
  RAIIn first,
  RAIIn last,
  RAIOut output_iterator,
  ReturnType neutral,
  ScanFunction scan,
  TransformationFunction transformation,
  const embb::mtapi::ExecutionPolicy& policy
  ) {
  Scan(first, last, output_iterator, neutral, scan, transformation, policy, 0);
}

#endif // else DOXYGEN

/**
 * \}
 */

}  // namespace algorithms
}  // namespace embb

#include <embb/algorithms/internal/scan-inl.h>

#endif  // EMBB_ALGORITHMS_SCAN_H_