slice.hpp

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// Copyright (c) 2024 Simons Foundation
//
// Licensed under the Apache License, Version 2.0 (the "License");
// you may not use this file except in compliance with the License.
// You may obtain a copy of the License at
//
//     http://www.apache.org/licenses/LICENSE-2.0.txt
//
// Unless required by applicable law or agreed to in writing, software
// distributed under the License is distributed on an "AS IS" BASIS,
// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
// See the License for the specific language governing permissions and
// limitations under the License.
//
// Authors: Thomas Hahn, Olivier Parcollet, Nils Wentzell, chuffa

 
#ifndef _ITERTOOLS_SLICE_HPP
#define _ITERTOOLS_SLICE_HPP
 
#include "./utils.hpp"
 
#include <algorithm>
#include <cstddef>
#include <iterator>
#include <utility>
 
namespace itertools {

  template <typename R> struct sliced {
    R rg;

    std::ptrdiff_t start_idx;

    std::ptrdiff_t end_idx;

    using iterator = decltype(std::begin(rg));

    using const_iterator = decltype(std::cbegin(rg));

    [[nodiscard]] bool operator==(sliced const &) const = default;

    [[nodiscard]] std::ptrdiff_t size() const {
      std::ptrdiff_t total_size = distance(std::cbegin(rg), std::cend(rg));
      return std::min(total_size, end_idx) - start_idx;
    }

    [[nodiscard]] iterator begin() noexcept { return std::next(std::begin(rg), start_idx); }

    [[nodiscard]] const_iterator cbegin() const noexcept { return std::next(std::cbegin(rg), start_idx); }

    [[nodiscard]] const_iterator begin() const noexcept { return cbegin(); }

    [[nodiscard]] iterator end() noexcept { return std::next(begin(), size()); }

    [[nodiscard]] const_iterator cend() const noexcept { return std::next(cbegin(), size()); }

    [[nodiscard]] const_iterator end() const noexcept { return cend(); }
  };

  template <typename R> [[nodiscard]] sliced<R> slice(R &&rg, std::ptrdiff_t start_idx, std::ptrdiff_t end_idx) {
    return {std::forward<R>(rg), start_idx, std::max(start_idx, end_idx)};
  }
 
} // namespace itertools
 
#endif // _ITERTOOLS_SLICE_HPP