1  // Copyright (c) 2022-present The Bitcoin Core developers
  2  // Distributed under the MIT software license, see the accompanying
  3  // file COPYING or http://www.opensource.org/licenses/mit-license.php.
  4  
  5  #ifndef BITCOIN_UTIL_BITDEQUE_H
  6  #define BITCOIN_UTIL_BITDEQUE_H
  7  
  8  #include <bitset>
  9  #include <cstddef>
 10  #include <deque>
 11  #include <limits>
 12  #include <stdexcept>
 13  #include <tuple>
 14  #include <util/overflow.h>
 15  
 16  /** Class that mimics std::deque<bool>, but with std::vector<bool>'s bit packing.
 17   *
 18   * BITS_PER_WORD selects the (minimum) number of bits that are allocated at once.
 19   * Larger values reduce the asymptotic memory usage overhead, at the cost of
 20   * needing larger up-front allocations. The default is 4096 bytes.
 21   */
 22  template<int BITS_PER_WORD = 4096 * 8>
 23  class bitdeque
 24  {
 25      // Internal definitions
 26      using word_type = std::bitset<BITS_PER_WORD>;
 27      using deque_type = std::deque<word_type>;
 28      static_assert(BITS_PER_WORD > 0);
 29  
 30      // Forward and friend declarations of iterator types.
 31      template<bool Const> class Iterator;
 32      template<bool Const> friend class Iterator;
 33  
 34      /** Iterator to a bitdeque element, const or not. */
 35      template<bool Const>
 36      class Iterator
 37      {
 38          using deque_iterator = std::conditional_t<Const, typename deque_type::const_iterator, typename deque_type::iterator>;
 39  
 40          deque_iterator m_it;
 41          int m_bitpos{0};
 42          Iterator(const deque_iterator& it, int bitpos) : m_it(it), m_bitpos(bitpos) {}
 43          friend class bitdeque;
 44  
 45      public:
 46          using iterator_category = std::random_access_iterator_tag;
 47          using value_type = bool;
 48          using pointer = void;
 49          using const_pointer = void;
 50          using reference = std::conditional_t<Const, bool, typename word_type::reference>;
 51          using const_reference = bool;
 52          using difference_type = std::ptrdiff_t;
 53  
 54          /** Default constructor. */
 55          Iterator() = default;
 56  
 57          /** Default copy constructor. */
 58          Iterator(const Iterator&) = default;
 59  
 60          /** Conversion from non-const to const iterator. */
 61          template<bool ConstArg = Const, typename = std::enable_if_t<Const && ConstArg>>
 62          Iterator(const Iterator<false>& x) : m_it(x.m_it), m_bitpos(x.m_bitpos) {}
 63  
 64          Iterator& operator+=(difference_type dist)
 65          {
 66              if (dist > 0) {
 67                  if (dist + m_bitpos >= BITS_PER_WORD) {
 68                      ++m_it;
 69                      dist -= BITS_PER_WORD - m_bitpos;
 70                      m_bitpos = 0;
 71                  }
 72                  auto jump = dist / BITS_PER_WORD;
 73                  m_it += jump;
 74                  m_bitpos += dist - jump * BITS_PER_WORD;
 75              } else if (dist < 0) {
 76                  dist = -dist;
 77                  if (dist > m_bitpos) {
 78                      --m_it;
 79                      dist -= m_bitpos + 1;
 80                      m_bitpos = BITS_PER_WORD - 1;
 81                  }
 82                  auto jump = dist / BITS_PER_WORD;
 83                  m_it -= jump;
 84                  m_bitpos -= dist - jump * BITS_PER_WORD;
 85              }
 86              return *this;
 87          }
 88  
 89          friend difference_type operator-(const Iterator& x, const Iterator& y)
 90          {
 91              return BITS_PER_WORD * (x.m_it - y.m_it) + x.m_bitpos - y.m_bitpos;
 92          }
 93  
 94          Iterator& operator=(const Iterator&) = default;
 95          Iterator& operator-=(difference_type dist) { return operator+=(-dist); }
 96          Iterator& operator++() { ++m_bitpos; if (m_bitpos == BITS_PER_WORD) { m_bitpos = 0; ++m_it; }; return *this; }
 97          Iterator operator++(int) { auto ret{*this}; operator++(); return ret; }
 98          Iterator& operator--() { if (m_bitpos == 0) { m_bitpos = BITS_PER_WORD; --m_it; }; --m_bitpos; return *this; }
 99          Iterator operator--(int) { auto ret{*this}; operator--(); return ret; }
100          friend Iterator operator+(Iterator x, difference_type dist) { x += dist; return x; }
101          friend Iterator operator+(difference_type dist, Iterator x) { x += dist; return x; }
102          friend Iterator operator-(Iterator x, difference_type dist) { x -= dist; return x; }
103          friend auto operator<=>(const Iterator& x, const Iterator& y) { return std::tie(x.m_it, x.m_bitpos) <=> std::tie(y.m_it, y.m_bitpos); }
104          friend bool operator==(const Iterator& x, const Iterator& y) { return x.m_it == y.m_it && x.m_bitpos == y.m_bitpos; }
105          reference operator*() const { return (*m_it)[m_bitpos]; }
106          reference operator[](difference_type pos) const { return *(*this + pos); }
107      };
108  
109  public:
110      using value_type = bool;
111      using size_type = std::size_t;
112      using difference_type = typename deque_type::difference_type;
113      using reference = typename word_type::reference;
114      using const_reference = bool;
115      using iterator = Iterator<false>;
116      using const_iterator = Iterator<true>;
117      using pointer = void;
118      using const_pointer = void;
119      using reverse_iterator = std::reverse_iterator<iterator>;
120      using const_reverse_iterator = std::reverse_iterator<const_iterator>;
121  
122  private:
123      /** Deque of bitsets storing the actual bit data. */
124      deque_type m_deque;
125  
126      /** Number of unused bits at the front of m_deque.front(). */
127      int m_pad_begin;
128  
129      /** Number of unused bits at the back of m_deque.back(). */
130      int m_pad_end;
131  
132      /** Shrink the container by n bits, removing from the end. */
133      void erase_back(size_type n)
134      {
135          if (n >= static_cast<size_type>(BITS_PER_WORD - m_pad_end)) {
136              n -= BITS_PER_WORD - m_pad_end;
137              m_pad_end = 0;
138              m_deque.erase(m_deque.end() - 1 - (n / BITS_PER_WORD), m_deque.end());
139              n %= BITS_PER_WORD;
140          }
141          if (n) {
142              auto& last = m_deque.back();
143              while (n) {
144                  last.reset(BITS_PER_WORD - 1 - m_pad_end);
145                  ++m_pad_end;
146                  --n;
147              }
148          }
149      }
150  
151      /** Extend the container by n bits, adding at the end. */
152      void extend_back(size_type n)
153      {
154          if (n > static_cast<size_type>(m_pad_end)) {
155              n -= m_pad_end + 1;
156              m_pad_end = BITS_PER_WORD - 1;
157              m_deque.insert(m_deque.end(), 1 + (n / BITS_PER_WORD), {});
158              n %= BITS_PER_WORD;
159          }
160          m_pad_end -= n;
161      }
162  
163      /** Shrink the container by n bits, removing from the beginning. */
164      void erase_front(size_type n)
165      {
166          if (n >= static_cast<size_type>(BITS_PER_WORD - m_pad_begin)) {
167              n -= BITS_PER_WORD - m_pad_begin;
168              m_pad_begin = 0;
169              m_deque.erase(m_deque.begin(), m_deque.begin() + 1 + (n / BITS_PER_WORD));
170              n %= BITS_PER_WORD;
171          }
172          if (n) {
173              auto& first = m_deque.front();
174              while (n) {
175                  first.reset(m_pad_begin);
176                  ++m_pad_begin;
177                  --n;
178              }
179          }
180      }
181  
182      /** Extend the container by n bits, adding at the beginning. */
183      void extend_front(size_type n)
184      {
185          if (n > static_cast<size_type>(m_pad_begin)) {
186              n -= m_pad_begin + 1;
187              m_pad_begin = BITS_PER_WORD - 1;
188              m_deque.insert(m_deque.begin(), 1 + (n / BITS_PER_WORD), {});
189              n %= BITS_PER_WORD;
190          }
191          m_pad_begin -= n;
192      }
193  
194      /** Insert a sequence of falses anywhere in the container. */
195      void insert_zeroes(size_type before, size_type count)
196      {
197          size_type after = size() - before;
198          if (before < after) {
199              extend_front(count);
200              std::move(begin() + count, begin() + count + before, begin());
201          } else {
202              extend_back(count);
203              std::move_backward(begin() + before, begin() + before + after, end());
204          }
205      }
206  
207  public:
208      /** Construct an empty container. */
209      explicit bitdeque() : m_pad_begin{0}, m_pad_end{0} {}
210  
211      /** Set the container equal to count times the value of val. */
212      void assign(size_type count, bool val)
213      {
214          m_deque.clear();
215          m_deque.resize(CeilDiv(count, size_type{BITS_PER_WORD}));
216          m_pad_begin = 0;
217          m_pad_end = 0;
218          if (val) {
219              for (auto& elem : m_deque) elem.flip();
220          }
221          if (count % BITS_PER_WORD) {
222              erase_back(BITS_PER_WORD - (count % BITS_PER_WORD));
223          }
224      }
225  
226      /** Construct a container containing count times the value of val. */
227      bitdeque(size_type count, bool val) { assign(count, val); }
228  
229      /** Construct a container containing count false values. */
230      explicit bitdeque(size_t count) { assign(count, false); }
231  
232      /** Copy constructor. */
233      bitdeque(const bitdeque&) = default;
234  
235      /** Move constructor. */
236      bitdeque(bitdeque&&) noexcept = default;
237  
238      /** Copy assignment operator. */
239      bitdeque& operator=(const bitdeque& other) = default;
240  
241      /** Move assignment operator. */
242      bitdeque& operator=(bitdeque&& other) noexcept = default;
243  
244      // Iterator functions.
245      iterator begin() noexcept { return {m_deque.begin(), m_pad_begin}; }
246      iterator end() noexcept { return iterator{m_deque.end(), 0} - m_pad_end; }
247      const_iterator begin() const noexcept { return const_iterator{m_deque.cbegin(), m_pad_begin}; }
248      const_iterator cbegin() const noexcept { return const_iterator{m_deque.cbegin(), m_pad_begin}; }
249      const_iterator end() const noexcept { return const_iterator{m_deque.cend(), 0} - m_pad_end; }
250      const_iterator cend() const noexcept { return const_iterator{m_deque.cend(), 0} - m_pad_end; }
251      reverse_iterator rbegin() noexcept { return reverse_iterator{end()}; }
252      reverse_iterator rend() noexcept { return reverse_iterator{begin()}; }
253      const_reverse_iterator rbegin() const noexcept { return const_reverse_iterator{cend()}; }
254      const_reverse_iterator crbegin() const noexcept { return const_reverse_iterator{cend()}; }
255      const_reverse_iterator rend() const noexcept { return const_reverse_iterator{cbegin()}; }
256      const_reverse_iterator crend() const noexcept { return const_reverse_iterator{cbegin()}; }
257  
258      /** Count the number of bits in the container. */
259      size_type size() const noexcept { return m_deque.size() * BITS_PER_WORD - m_pad_begin - m_pad_end; }
260  
261      /** Determine whether the container is empty. */
262      bool empty() const noexcept
263      {
264          return m_deque.size() == 0 || (m_deque.size() == 1 && (m_pad_begin + m_pad_end == BITS_PER_WORD));
265      }
266  
267      /** Return the maximum size of the container. */
268      size_type max_size() const noexcept
269      {
270          if (m_deque.max_size() < std::numeric_limits<difference_type>::max() / BITS_PER_WORD) {
271              return m_deque.max_size() * BITS_PER_WORD;
272          } else {
273              return std::numeric_limits<difference_type>::max();
274          }
275      }
276  
277      /** Set the container equal to the bits in [first,last). */
278      template<typename It>
279      void assign(It first, It last)
280      {
281          size_type count = std::distance(first, last);
282          assign(count, false);
283          auto it = begin();
284          while (first != last) {
285              *(it++) = *(first++);
286          }
287      }
288  
289      /** Set the container equal to the bits in ilist. */
290      void assign(std::initializer_list<bool> ilist)
291      {
292          assign(ilist.size(), false);
293          auto it = begin();
294          auto init = ilist.begin();
295          while (init != ilist.end()) {
296              *(it++) = *(init++);
297          }
298      }
299  
300      /** Set the container equal to the bits in ilist. */
301      bitdeque& operator=(std::initializer_list<bool> ilist)
302      {
303          assign(ilist);
304          return *this;
305      }
306  
307      /** Construct a container containing the bits in [first,last). */
308      template<typename It>
309      bitdeque(It first, It last) { assign(first, last); }
310  
311      /** Construct a container containing the bits in ilist. */
312      bitdeque(std::initializer_list<bool> ilist) { assign(ilist); }
313  
314      // Access an element of the container, with bounds checking.
315      reference at(size_type position)
316      {
317          if (position >= size()) throw std::out_of_range("bitdeque::at() out of range");
318          return begin()[position];
319      }
320      const_reference at(size_type position) const
321      {
322          if (position >= size()) throw std::out_of_range("bitdeque::at() out of range");
323          return cbegin()[position];
324      }
325  
326      // Access elements of the container without bounds checking.
327      reference operator[](size_type position) { return begin()[position]; }
328      const_reference operator[](size_type position) const { return cbegin()[position]; }
329      reference front() { return *begin(); }
330      const_reference front() const { return *cbegin(); }
331      reference back() { return end()[-1]; }
332      const_reference back() const { return cend()[-1]; }
333  
334      /** Release unused memory. */
335      void shrink_to_fit()
336      {
337          m_deque.shrink_to_fit();
338      }
339  
340      /** Empty the container. */
341      void clear() noexcept
342      {
343          m_deque.clear();
344          m_pad_begin = m_pad_end = 0;
345      }
346  
347      // Append an element to the container.
348      void push_back(bool val)
349      {
350          extend_back(1);
351          back() = val;
352      }
353      reference emplace_back(bool val)
354      {
355          extend_back(1);
356          auto ref = back();
357          ref = val;
358          return ref;
359      }
360  
361      // Prepend an element to the container.
362      void push_front(bool val)
363      {
364          extend_front(1);
365          front() = val;
366      }
367      reference emplace_front(bool val)
368      {
369          extend_front(1);
370          auto ref = front();
371          ref = val;
372          return ref;
373      }
374  
375      // Remove the last element from the container.
376      void pop_back()
377      {
378          erase_back(1);
379      }
380  
381      // Remove the first element from the container.
382      void pop_front()
383      {
384          erase_front(1);
385      }
386  
387      /** Resize the container. */
388      void resize(size_type n)
389      {
390          if (n < size()) {
391              erase_back(size() - n);
392          } else {
393              extend_back(n - size());
394          }
395      }
396  
397      // Swap two containers.
398      void swap(bitdeque& other) noexcept
399      {
400          std::swap(m_deque, other.m_deque);
401          std::swap(m_pad_begin, other.m_pad_begin);
402          std::swap(m_pad_end, other.m_pad_end);
403      }
404      friend void swap(bitdeque& b1, bitdeque& b2) noexcept { b1.swap(b2); }
405  
406      // Erase elements from the container.
407      iterator erase(const_iterator first, const_iterator last)
408      {
409          size_type before = std::distance(cbegin(), first);
410          size_type dist = std::distance(first, last);
411          size_type after = std::distance(last, cend());
412          if (before < after) {
413              std::move_backward(begin(), begin() + before, end() - after);
414              erase_front(dist);
415              return begin() + before;
416          } else {
417              std::move(end() - after, end(), begin() + before);
418              erase_back(dist);
419              return end() - after;
420          }
421      }
422  
423      iterator erase(iterator first, iterator last) { return erase(const_iterator{first}, const_iterator{last}); }
424      iterator erase(const_iterator pos) { return erase(pos, pos + 1); }
425      iterator erase(iterator pos) { return erase(const_iterator{pos}, const_iterator{pos} + 1); }
426  
427      // Insert elements into the container.
428      iterator insert(const_iterator pos, bool val)
429      {
430          size_type before = pos - cbegin();
431          insert_zeroes(before, 1);
432          auto it = begin() + before;
433          *it = val;
434          return it;
435      }
436  
437      iterator emplace(const_iterator pos, bool val) { return insert(pos, val); }
438  
439      iterator insert(const_iterator pos, size_type count, bool val)
440      {
441          size_type before = pos - cbegin();
442          insert_zeroes(before, count);
443          auto it_begin = begin() + before;
444          auto it = it_begin;
445          auto it_end = it + count;
446          while (it != it_end) *(it++) = val;
447          return it_begin;
448      }
449  
450      template<typename It>
451      iterator insert(const_iterator pos, It first, It last)
452      {
453          size_type before = pos - cbegin();
454          size_type count = std::distance(first, last);
455          insert_zeroes(before, count);
456          auto it_begin = begin() + before;
457          auto it = it_begin;
458          while (first != last) {
459              *(it++) = *(first++);
460          }
461          return it_begin;
462      }
463  };
464  
465  #endif // BITCOIN_UTIL_BITDEQUE_H