entry.h

// Copyright 2025 The Pigweed Authors
//
// 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
//
//     https://www.apache.org/licenses/LICENSE-2.0
//
// 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.
#pragma once
 
#include <cstddef>
#include <cstdint>
#include <limits>
 
#include "pw_allocator/deallocator.h"
#include "pw_allocator/internal/control_block.h"
 
namespace pw::multibuf::internal {
 
union Entry {
  using size_type = uint16_t;
 
  static constexpr size_t kMaxSize = ~(1U << 15);
 
  static constexpr size_type kMemoryContextIndex = 0;
 
  static constexpr size_type kDataIndex = 1;
 
  static constexpr size_type kBaseViewIndex = 2;
 
  static constexpr size_type kMinEntriesPerChunk = 3;
 
  static constexpr size_type memory_context_index(size_type chunk,
                                                  size_type entries_per_chunk) {
    return chunk * entries_per_chunk + kMemoryContextIndex;
  }
 
  static constexpr size_type data_index(size_type chunk,
                                        size_type entries_per_chunk) {
    return chunk * entries_per_chunk + kDataIndex;
  }
 
  static constexpr size_type base_view_index(size_type chunk,
                                             size_type entries_per_chunk) {
    return chunk * entries_per_chunk + kBaseViewIndex;
  }
 
  static constexpr size_type view_index(size_type chunk,
                                        size_type entries_per_chunk,
                                        size_type layer) {
    return chunk * entries_per_chunk + kBaseViewIndex + layer - 1;
  }
 
  static constexpr size_type top_view_index(size_type chunk,
                                            size_type entries_per_chunk) {
    return (chunk + 1) * entries_per_chunk - 1;
  }
 
  Deallocator* deallocator;
 
  allocator::internal::ControlBlock* control_block;
 
  std::byte* data;
 
  struct BaseView {
    size_type offset : 15;
 
    size_type owned : 1;
 
    size_type length : 15;
 
    size_type shared : 1;
  } base_view;
 
  struct View {
    size_type offset : 15;
 
    size_type sealed : 1;
 
    size_type length : 15;
 
    size_type boundary : 1;
  } view;
};
 
}  // namespace pw::multibuf::internal