1 use crate::vec::{Idx, IndexVec};
2 use smallvec::SmallVec;
5 use std::marker::PhantomData;
13 pub const WORD_BYTES: usize = mem::size_of::<Word>();
14 pub const WORD_BITS: usize = WORD_BYTES * 8;
16 /// A fixed-size bitset type with a dense representation. It does not support
17 /// resizing after creation; use `GrowableBitSet` for that.
19 /// `T` is an index type, typically a newtyped `usize` wrapper, but it can also
22 /// All operations that involve an element will panic if the element is equal
23 /// to or greater than the domain size. All operations that involve two bitsets
24 /// will panic if the bitsets have differing domain sizes.
25 #[derive(Clone, Eq, PartialEq, RustcDecodable, RustcEncodable)]
26 pub struct BitSet<T: Idx> {
29 marker: PhantomData<T>,
32 impl<T: Idx> BitSet<T> {
33 /// Creates a new, empty bitset with a given `domain_size`.
35 pub fn new_empty(domain_size: usize) -> BitSet<T> {
36 let num_words = num_words(domain_size);
39 words: vec![0; num_words],
44 /// Creates a new, filled bitset with a given `domain_size`.
46 pub fn new_filled(domain_size: usize) -> BitSet<T> {
47 let num_words = num_words(domain_size);
48 let mut result = BitSet {
50 words: vec![!0; num_words],
53 result.clear_excess_bits();
57 /// Gets the domain size.
58 pub fn domain_size(&self) -> usize {
62 /// Clear all elements.
64 pub fn clear(&mut self) {
65 for word in &mut self.words {
70 /// Clear excess bits in the final word.
71 fn clear_excess_bits(&mut self) {
72 let num_bits_in_final_word = self.domain_size % WORD_BITS;
73 if num_bits_in_final_word > 0 {
74 let mask = (1 << num_bits_in_final_word) - 1;
75 let final_word_idx = self.words.len() - 1;
76 self.words[final_word_idx] &= mask;
80 /// Efficiently overwrite `self` with `other`.
81 pub fn overwrite(&mut self, other: &BitSet<T>) {
82 assert!(self.domain_size == other.domain_size);
83 self.words.clone_from_slice(&other.words);
86 /// Count the number of set bits in the set.
87 pub fn count(&self) -> usize {
88 self.words.iter().map(|e| e.count_ones() as usize).sum()
91 /// Returns `true` if `self` contains `elem`.
93 pub fn contains(&self, elem: T) -> bool {
94 assert!(elem.index() < self.domain_size);
95 let (word_index, mask) = word_index_and_mask(elem);
96 (self.words[word_index] & mask) != 0
99 /// Is `self` is a (non-strict) superset of `other`?
101 pub fn superset(&self, other: &BitSet<T>) -> bool {
102 assert_eq!(self.domain_size, other.domain_size);
103 self.words.iter().zip(&other.words).all(|(a, b)| (a & b) == *b)
106 /// Is the set empty?
108 pub fn is_empty(&self) -> bool {
109 self.words.iter().all(|a| *a == 0)
112 /// Insert `elem`. Returns whether the set has changed.
114 pub fn insert(&mut self, elem: T) -> bool {
115 assert!(elem.index() < self.domain_size);
116 let (word_index, mask) = word_index_and_mask(elem);
117 let word_ref = &mut self.words[word_index];
118 let word = *word_ref;
119 let new_word = word | mask;
120 *word_ref = new_word;
124 /// Sets all bits to true.
125 pub fn insert_all(&mut self) {
126 for word in &mut self.words {
129 self.clear_excess_bits();
132 /// Returns `true` if the set has changed.
134 pub fn remove(&mut self, elem: T) -> bool {
135 assert!(elem.index() < self.domain_size);
136 let (word_index, mask) = word_index_and_mask(elem);
137 let word_ref = &mut self.words[word_index];
138 let word = *word_ref;
139 let new_word = word & !mask;
140 *word_ref = new_word;
144 /// Sets `self = self | other` and returns `true` if `self` changed
145 /// (i.e., if new bits were added).
146 pub fn union(&mut self, other: &impl UnionIntoBitSet<T>) -> bool {
147 other.union_into(self)
150 /// Sets `self = self - other` and returns `true` if `self` changed.
151 /// (i.e., if any bits were removed).
152 pub fn subtract(&mut self, other: &impl SubtractFromBitSet<T>) -> bool {
153 other.subtract_from(self)
156 /// Sets `self = self & other` and return `true` if `self` changed.
157 /// (i.e., if any bits were removed).
158 pub fn intersect(&mut self, other: &BitSet<T>) -> bool {
159 assert_eq!(self.domain_size, other.domain_size);
160 bitwise(&mut self.words, &other.words, |a, b| { a & b })
163 /// Gets a slice of the underlying words.
164 pub fn words(&self) -> &[Word] {
168 /// Iterates over the indices of set bits in a sorted order.
170 pub fn iter(&self) -> BitIter<'_, T> {
173 iter: self.words.iter().enumerate(),
178 /// Duplicates the set as a hybrid set.
179 pub fn to_hybrid(&self) -> HybridBitSet<T> {
180 // Note: we currently don't bother trying to make a Sparse set.
181 HybridBitSet::Dense(self.to_owned())
184 /// Set `self = self | other`. In contrast to `union` returns `true` if the set contains at
185 /// least one bit that is not in `other` (i.e. `other` is not a superset of `self`).
187 /// This is an optimization for union of a hybrid bitset.
188 fn reverse_union_sparse(&mut self, sparse: &SparseBitSet<T>) -> bool {
189 assert!(sparse.domain_size == self.domain_size);
190 self.clear_excess_bits();
192 let mut not_already = false;
193 // Index of the current word not yet merged.
194 let mut current_index = 0;
195 // Mask of bits that came from the sparse set in the current word.
196 let mut new_bit_mask = 0;
197 for (word_index, mask) in sparse.iter().map(|x| word_index_and_mask(*x)) {
198 // Next bit is in a word not inspected yet.
199 if word_index > current_index {
200 self.words[current_index] |= new_bit_mask;
201 // Were there any bits in the old word that did not occur in the sparse set?
202 not_already |= (self.words[current_index] ^ new_bit_mask) != 0;
203 // Check all words we skipped for any set bit.
204 not_already |= self.words[current_index+1..word_index].iter().any(|&x| x != 0);
206 current_index = word_index;
207 // Reset bit mask, no bits have been merged yet.
210 // Add bit and mark it as coming from the sparse set.
211 // self.words[word_index] |= mask;
212 new_bit_mask |= mask;
214 self.words[current_index] |= new_bit_mask;
215 // Any bits in the last inspected word that were not in the sparse set?
216 not_already |= (self.words[current_index] ^ new_bit_mask) != 0;
217 // Any bits in the tail? Note `clear_excess_bits` before.
218 not_already |= self.words[current_index+1..].iter().any(|&x| x != 0);
224 /// This is implemented by all the bitsets so that BitSet::union() can be
225 /// passed any type of bitset.
226 pub trait UnionIntoBitSet<T: Idx> {
227 // Performs `other = other | self`.
228 fn union_into(&self, other: &mut BitSet<T>) -> bool;
231 /// This is implemented by all the bitsets so that BitSet::subtract() can be
232 /// passed any type of bitset.
233 pub trait SubtractFromBitSet<T: Idx> {
234 // Performs `other = other - self`.
235 fn subtract_from(&self, other: &mut BitSet<T>) -> bool;
238 impl<T: Idx> UnionIntoBitSet<T> for BitSet<T> {
239 fn union_into(&self, other: &mut BitSet<T>) -> bool {
240 assert_eq!(self.domain_size, other.domain_size);
241 bitwise(&mut other.words, &self.words, |a, b| { a | b })
245 impl<T: Idx> SubtractFromBitSet<T> for BitSet<T> {
246 fn subtract_from(&self, other: &mut BitSet<T>) -> bool {
247 assert_eq!(self.domain_size, other.domain_size);
248 bitwise(&mut other.words, &self.words, |a, b| { a & !b })
252 impl<T: Idx> fmt::Debug for BitSet<T> {
253 fn fmt(&self, w: &mut fmt::Formatter<'_>) -> fmt::Result {
255 .entries(self.iter())
260 impl<T: Idx> ToString for BitSet<T> {
261 fn to_string(&self) -> String {
262 let mut result = String::new();
265 // Note: this is a little endian printout of bytes.
267 // i tracks how many bits we have printed so far.
269 for word in &self.words {
270 let mut word = *word;
271 for _ in 0..WORD_BYTES { // for each byte in `word`:
272 let remain = self.domain_size - i;
273 // If less than a byte remains, then mask just that many bits.
274 let mask = if remain <= 8 { (1 << remain) - 1 } else { 0xFF };
275 assert!(mask <= 0xFF);
276 let byte = word & mask;
278 result.push_str(&format!("{}{:02x}", sep, byte));
280 if remain <= 8 { break; }
293 pub struct BitIter<'a, T: Idx> {
294 cur: Option<(Word, usize)>,
295 iter: iter::Enumerate<slice::Iter<'a, Word>>,
296 marker: PhantomData<T>
299 impl<'a, T: Idx> Iterator for BitIter<'a, T> {
301 fn next(&mut self) -> Option<T> {
303 if let Some((ref mut word, offset)) = self.cur {
304 let bit_pos = word.trailing_zeros() as usize;
305 if bit_pos != WORD_BITS {
306 let bit = 1 << bit_pos;
308 return Some(T::new(bit_pos + offset))
312 let (i, word) = self.iter.next()?;
313 self.cur = Some((*word, WORD_BITS * i));
319 fn bitwise<Op>(out_vec: &mut [Word], in_vec: &[Word], op: Op) -> bool
320 where Op: Fn(Word, Word) -> Word
322 assert_eq!(out_vec.len(), in_vec.len());
323 let mut changed = false;
324 for (out_elem, in_elem) in out_vec.iter_mut().zip(in_vec.iter()) {
325 let old_val = *out_elem;
326 let new_val = op(old_val, *in_elem);
328 changed |= old_val != new_val;
333 const SPARSE_MAX: usize = 8;
335 /// A fixed-size bitset type with a sparse representation and a maximum of
336 /// `SPARSE_MAX` elements. The elements are stored as a sorted `SmallVec` with
337 /// no duplicates; although `SmallVec` can spill its elements to the heap, that
338 /// never happens within this type because of the `SPARSE_MAX` limit.
340 /// This type is used by `HybridBitSet`; do not use directly.
341 #[derive(Clone, Debug)]
342 pub struct SparseBitSet<T: Idx> {
344 elems: SmallVec<[T; SPARSE_MAX]>,
347 impl<T: Idx> SparseBitSet<T> {
348 fn new_empty(domain_size: usize) -> Self {
351 elems: SmallVec::new()
355 fn len(&self) -> usize {
359 fn is_empty(&self) -> bool {
360 self.elems.len() == 0
363 fn contains(&self, elem: T) -> bool {
364 assert!(elem.index() < self.domain_size);
365 self.elems.contains(&elem)
368 fn insert(&mut self, elem: T) -> bool {
369 assert!(elem.index() < self.domain_size);
370 let changed = if let Some(i) = self.elems.iter().position(|&e| e >= elem) {
371 if self.elems[i] == elem {
372 // `elem` is already in the set.
375 // `elem` is smaller than one or more existing elements.
376 self.elems.insert(i, elem);
380 // `elem` is larger than all existing elements.
381 self.elems.push(elem);
384 assert!(self.len() <= SPARSE_MAX);
388 fn remove(&mut self, elem: T) -> bool {
389 assert!(elem.index() < self.domain_size);
390 if let Some(i) = self.elems.iter().position(|&e| e == elem) {
391 self.elems.remove(i);
398 fn to_dense(&self) -> BitSet<T> {
399 let mut dense = BitSet::new_empty(self.domain_size);
400 for elem in self.elems.iter() {
406 fn iter(&self) -> slice::Iter<'_, T> {
411 impl<T: Idx> UnionIntoBitSet<T> for SparseBitSet<T> {
412 fn union_into(&self, other: &mut BitSet<T>) -> bool {
413 assert_eq!(self.domain_size, other.domain_size);
414 let mut changed = false;
415 for elem in self.iter() {
416 changed |= other.insert(*elem);
422 impl<T: Idx> SubtractFromBitSet<T> for SparseBitSet<T> {
423 fn subtract_from(&self, other: &mut BitSet<T>) -> bool {
424 assert_eq!(self.domain_size, other.domain_size);
425 let mut changed = false;
426 for elem in self.iter() {
427 changed |= other.remove(*elem);
433 /// A fixed-size bitset type with a hybrid representation: sparse when there
434 /// are up to a `SPARSE_MAX` elements in the set, but dense when there are more
435 /// than `SPARSE_MAX`.
437 /// This type is especially efficient for sets that typically have a small
438 /// number of elements, but a large `domain_size`, and are cleared frequently.
440 /// `T` is an index type, typically a newtyped `usize` wrapper, but it can also
443 /// All operations that involve an element will panic if the element is equal
444 /// to or greater than the domain size. All operations that involve two bitsets
445 /// will panic if the bitsets have differing domain sizes.
446 #[derive(Clone, Debug)]
447 pub enum HybridBitSet<T: Idx> {
448 Sparse(SparseBitSet<T>),
452 impl<T: Idx> HybridBitSet<T> {
453 pub fn new_empty(domain_size: usize) -> Self {
454 HybridBitSet::Sparse(SparseBitSet::new_empty(domain_size))
457 fn domain_size(&self) -> usize {
459 HybridBitSet::Sparse(sparse) => sparse.domain_size,
460 HybridBitSet::Dense(dense) => dense.domain_size,
464 pub fn clear(&mut self) {
465 let domain_size = self.domain_size();
466 *self = HybridBitSet::new_empty(domain_size);
469 pub fn contains(&self, elem: T) -> bool {
471 HybridBitSet::Sparse(sparse) => sparse.contains(elem),
472 HybridBitSet::Dense(dense) => dense.contains(elem),
476 pub fn superset(&self, other: &HybridBitSet<T>) -> bool {
477 match (self, other) {
478 (HybridBitSet::Dense(self_dense), HybridBitSet::Dense(other_dense)) => {
479 self_dense.superset(other_dense)
482 assert!(self.domain_size() == other.domain_size());
483 other.iter().all(|elem| self.contains(elem))
488 pub fn is_empty(&self) -> bool {
490 HybridBitSet::Sparse(sparse) => sparse.is_empty(),
491 HybridBitSet::Dense(dense) => dense.is_empty(),
495 pub fn insert(&mut self, elem: T) -> bool {
496 // No need to check `elem` against `self.domain_size` here because all
497 // the match cases check it, one way or another.
499 HybridBitSet::Sparse(sparse) if sparse.len() < SPARSE_MAX => {
500 // The set is sparse and has space for `elem`.
503 HybridBitSet::Sparse(sparse) if sparse.contains(elem) => {
504 // The set is sparse and does not have space for `elem`, but
505 // that doesn't matter because `elem` is already present.
508 HybridBitSet::Sparse(sparse) => {
509 // The set is sparse and full. Convert to a dense set.
510 let mut dense = sparse.to_dense();
511 let changed = dense.insert(elem);
513 *self = HybridBitSet::Dense(dense);
516 HybridBitSet::Dense(dense) => dense.insert(elem),
520 pub fn insert_all(&mut self) {
521 let domain_size = self.domain_size();
523 HybridBitSet::Sparse(_) => {
524 *self = HybridBitSet::Dense(BitSet::new_filled(domain_size));
526 HybridBitSet::Dense(dense) => dense.insert_all(),
530 pub fn remove(&mut self, elem: T) -> bool {
531 // Note: we currently don't bother going from Dense back to Sparse.
533 HybridBitSet::Sparse(sparse) => sparse.remove(elem),
534 HybridBitSet::Dense(dense) => dense.remove(elem),
538 pub fn union(&mut self, other: &HybridBitSet<T>) -> bool {
540 HybridBitSet::Sparse(self_sparse) => {
542 HybridBitSet::Sparse(other_sparse) => {
543 // Both sets are sparse. Add the elements in
544 // `other_sparse` to `self` one at a time. This
545 // may or may not cause `self` to be densified.
546 assert_eq!(self.domain_size(), other.domain_size());
547 let mut changed = false;
548 for elem in other_sparse.iter() {
549 changed |= self.insert(*elem);
553 HybridBitSet::Dense(other_dense) => {
554 // `self` is sparse and `other` is dense. To
555 // merge them, we have two available strategies:
556 // * Densify `self` then merge other
557 // * Clone other then integrate bits from `self`
558 // The second strategy requires dedicated method
559 // since the usual `union` returns the wrong
560 // result. In the dedicated case the computation
561 // is slightly faster if the bits of the sparse
562 // bitset map to only few words of the dense
563 // representation, i.e. indices are near each
566 // Benchmarking seems to suggest that the second
567 // option is worth it.
568 let mut new_dense = other_dense.clone();
569 let changed = new_dense.reverse_union_sparse(self_sparse);
570 *self = HybridBitSet::Dense(new_dense);
576 HybridBitSet::Dense(self_dense) => self_dense.union(other),
580 /// Converts to a dense set, consuming itself in the process.
581 pub fn to_dense(self) -> BitSet<T> {
583 HybridBitSet::Sparse(sparse) => sparse.to_dense(),
584 HybridBitSet::Dense(dense) => dense,
588 pub fn iter(&self) -> HybridIter<'_, T> {
590 HybridBitSet::Sparse(sparse) => HybridIter::Sparse(sparse.iter()),
591 HybridBitSet::Dense(dense) => HybridIter::Dense(dense.iter()),
596 impl<T: Idx> UnionIntoBitSet<T> for HybridBitSet<T> {
597 fn union_into(&self, other: &mut BitSet<T>) -> bool {
599 HybridBitSet::Sparse(sparse) => sparse.union_into(other),
600 HybridBitSet::Dense(dense) => dense.union_into(other),
605 impl<T: Idx> SubtractFromBitSet<T> for HybridBitSet<T> {
606 fn subtract_from(&self, other: &mut BitSet<T>) -> bool {
608 HybridBitSet::Sparse(sparse) => sparse.subtract_from(other),
609 HybridBitSet::Dense(dense) => dense.subtract_from(other),
614 pub enum HybridIter<'a, T: Idx> {
615 Sparse(slice::Iter<'a, T>),
616 Dense(BitIter<'a, T>),
619 impl<'a, T: Idx> Iterator for HybridIter<'a, T> {
622 fn next(&mut self) -> Option<T> {
624 HybridIter::Sparse(sparse) => sparse.next().copied(),
625 HybridIter::Dense(dense) => dense.next(),
630 /// A resizable bitset type with a dense representation.
632 /// `T` is an index type, typically a newtyped `usize` wrapper, but it can also
635 /// All operations that involve an element will panic if the element is equal
636 /// to or greater than the domain size.
637 #[derive(Clone, Debug, PartialEq)]
638 pub struct GrowableBitSet<T: Idx> {
642 impl<T: Idx> GrowableBitSet<T> {
643 /// Ensure that the set can hold at least `min_domain_size` elements.
644 pub fn ensure(&mut self, min_domain_size: usize) {
645 if self.bit_set.domain_size < min_domain_size {
646 self.bit_set.domain_size = min_domain_size;
649 let min_num_words = num_words(min_domain_size);
650 if self.bit_set.words.len() < min_num_words {
651 self.bit_set.words.resize(min_num_words, 0)
655 pub fn new_empty() -> GrowableBitSet<T> {
656 GrowableBitSet { bit_set: BitSet::new_empty(0) }
659 pub fn with_capacity(capacity: usize) -> GrowableBitSet<T> {
660 GrowableBitSet { bit_set: BitSet::new_empty(capacity) }
663 /// Returns `true` if the set has changed.
665 pub fn insert(&mut self, elem: T) -> bool {
666 self.ensure(elem.index() + 1);
667 self.bit_set.insert(elem)
671 pub fn contains(&self, elem: T) -> bool {
672 let (word_index, mask) = word_index_and_mask(elem);
673 if let Some(word) = self.bit_set.words.get(word_index) {
681 /// A fixed-size 2D bit matrix type with a dense representation.
683 /// `R` and `C` are index types used to identify rows and columns respectively;
684 /// typically newtyped `usize` wrappers, but they can also just be `usize`.
686 /// All operations that involve a row and/or column index will panic if the
687 /// index exceeds the relevant bound.
688 #[derive(Clone, Debug, Eq, PartialEq, RustcDecodable, RustcEncodable)]
689 pub struct BitMatrix<R: Idx, C: Idx> {
693 marker: PhantomData<(R, C)>,
696 impl<R: Idx, C: Idx> BitMatrix<R, C> {
697 /// Creates a new `rows x columns` matrix, initially empty.
698 pub fn new(num_rows: usize, num_columns: usize) -> BitMatrix<R, C> {
699 // For every element, we need one bit for every other
700 // element. Round up to an even number of words.
701 let words_per_row = num_words(num_columns);
705 words: vec![0; num_rows * words_per_row],
710 /// Creates a new matrix, with `row` used as the value for every row.
711 pub fn from_row_n(row: &BitSet<C>, num_rows: usize) -> BitMatrix<R, C> {
712 let num_columns = row.domain_size();
713 let words_per_row = num_words(num_columns);
714 assert_eq!(words_per_row, row.words().len());
718 words: iter::repeat(row.words()).take(num_rows).flatten().cloned().collect(),
723 pub fn rows(&self) -> impl Iterator<Item = R> {
724 (0..self.num_rows).map(R::new)
727 /// The range of bits for a given row.
728 fn range(&self, row: R) -> (usize, usize) {
729 let words_per_row = num_words(self.num_columns);
730 let start = row.index() * words_per_row;
731 (start, start + words_per_row)
734 /// Sets the cell at `(row, column)` to true. Put another way, insert
735 /// `column` to the bitset for `row`.
737 /// Returns `true` if this changed the matrix.
738 pub fn insert(&mut self, row: R, column: C) -> bool {
739 assert!(row.index() < self.num_rows && column.index() < self.num_columns);
740 let (start, _) = self.range(row);
741 let (word_index, mask) = word_index_and_mask(column);
742 let words = &mut self.words[..];
743 let word = words[start + word_index];
744 let new_word = word | mask;
745 words[start + word_index] = new_word;
749 /// Do the bits from `row` contain `column`? Put another way, is
750 /// the matrix cell at `(row, column)` true? Put yet another way,
751 /// if the matrix represents (transitive) reachability, can
752 /// `row` reach `column`?
753 pub fn contains(&self, row: R, column: C) -> bool {
754 assert!(row.index() < self.num_rows && column.index() < self.num_columns);
755 let (start, _) = self.range(row);
756 let (word_index, mask) = word_index_and_mask(column);
757 (self.words[start + word_index] & mask) != 0
760 /// Returns those indices that are true in rows `a` and `b`. This
761 /// is an O(n) operation where `n` is the number of elements
762 /// (somewhat independent from the actual size of the
763 /// intersection, in particular).
764 pub fn intersect_rows(&self, row1: R, row2: R) -> Vec<C> {
765 assert!(row1.index() < self.num_rows && row2.index() < self.num_rows);
766 let (row1_start, row1_end) = self.range(row1);
767 let (row2_start, row2_end) = self.range(row2);
768 let mut result = Vec::with_capacity(self.num_columns);
769 for (base, (i, j)) in (row1_start..row1_end).zip(row2_start..row2_end).enumerate() {
770 let mut v = self.words[i] & self.words[j];
771 for bit in 0..WORD_BITS {
776 result.push(C::new(base * WORD_BITS + bit));
784 /// Adds the bits from row `read` to the bits from row `write`, and
785 /// returns `true` if anything changed.
787 /// This is used when computing transitive reachability because if
788 /// you have an edge `write -> read`, because in that case
789 /// `write` can reach everything that `read` can (and
790 /// potentially more).
791 pub fn union_rows(&mut self, read: R, write: R) -> bool {
792 assert!(read.index() < self.num_rows && write.index() < self.num_rows);
793 let (read_start, read_end) = self.range(read);
794 let (write_start, write_end) = self.range(write);
795 let words = &mut self.words[..];
796 let mut changed = false;
797 for (read_index, write_index) in (read_start..read_end).zip(write_start..write_end) {
798 let word = words[write_index];
799 let new_word = word | words[read_index];
800 words[write_index] = new_word;
801 changed |= word != new_word;
806 /// Adds the bits from `with` to the bits from row `write`, and
807 /// returns `true` if anything changed.
808 pub fn union_row_with(&mut self, with: &BitSet<C>, write: R) -> bool {
809 assert!(write.index() < self.num_rows);
810 assert_eq!(with.domain_size(), self.num_columns);
811 let (write_start, write_end) = self.range(write);
812 let mut changed = false;
813 for (read_index, write_index) in (0..with.words().len()).zip(write_start..write_end) {
814 let word = self.words[write_index];
815 let new_word = word | with.words()[read_index];
816 self.words[write_index] = new_word;
817 changed |= word != new_word;
822 /// Sets every cell in `row` to true.
823 pub fn insert_all_into_row(&mut self, row: R) {
824 assert!(row.index() < self.num_rows);
825 let (start, end) = self.range(row);
826 let words = &mut self.words[..];
827 for index in start..end {
830 self.clear_excess_bits(row);
833 /// Clear excess bits in the final word of the row.
834 fn clear_excess_bits(&mut self, row: R) {
835 let num_bits_in_final_word = self.num_columns % WORD_BITS;
836 if num_bits_in_final_word > 0 {
837 let mask = (1 << num_bits_in_final_word) - 1;
838 let (_, end) = self.range(row);
839 let final_word_idx = end - 1;
840 self.words[final_word_idx] &= mask;
844 /// Gets a slice of the underlying words.
845 pub fn words(&self) -> &[Word] {
849 /// Iterates through all the columns set to true in a given row of
851 pub fn iter(&self, row: R) -> BitIter<'_, C> {
852 assert!(row.index() < self.num_rows);
853 let (start, end) = self.range(row);
856 iter: self.words[start..end].iter().enumerate(),
861 /// Returns the number of elements in `row`.
862 pub fn count(&self, row: R) -> usize {
863 let (start, end) = self.range(row);
864 self.words[start..end].iter().map(|e| e.count_ones() as usize).sum()
868 /// A fixed-column-size, variable-row-size 2D bit matrix with a moderately
869 /// sparse representation.
871 /// Initially, every row has no explicit representation. If any bit within a
872 /// row is set, the entire row is instantiated as `Some(<HybridBitSet>)`.
873 /// Furthermore, any previously uninstantiated rows prior to it will be
874 /// instantiated as `None`. Those prior rows may themselves become fully
875 /// instantiated later on if any of their bits are set.
877 /// `R` and `C` are index types used to identify rows and columns respectively;
878 /// typically newtyped `usize` wrappers, but they can also just be `usize`.
879 #[derive(Clone, Debug)]
880 pub struct SparseBitMatrix<R, C>
886 rows: IndexVec<R, Option<HybridBitSet<C>>>,
889 impl<R: Idx, C: Idx> SparseBitMatrix<R, C> {
890 /// Creates a new empty sparse bit matrix with no rows or columns.
891 pub fn new(num_columns: usize) -> Self {
894 rows: IndexVec::new(),
898 fn ensure_row(&mut self, row: R) -> &mut HybridBitSet<C> {
899 // Instantiate any missing rows up to and including row `row` with an
900 // empty HybridBitSet.
901 self.rows.ensure_contains_elem(row, || None);
903 // Then replace row `row` with a full HybridBitSet if necessary.
904 let num_columns = self.num_columns;
905 self.rows[row].get_or_insert_with(|| HybridBitSet::new_empty(num_columns))
908 /// Sets the cell at `(row, column)` to true. Put another way, insert
909 /// `column` to the bitset for `row`.
911 /// Returns `true` if this changed the matrix.
912 pub fn insert(&mut self, row: R, column: C) -> bool {
913 self.ensure_row(row).insert(column)
916 /// Do the bits from `row` contain `column`? Put another way, is
917 /// the matrix cell at `(row, column)` true? Put yet another way,
918 /// if the matrix represents (transitive) reachability, can
919 /// `row` reach `column`?
920 pub fn contains(&self, row: R, column: C) -> bool {
921 self.row(row).map_or(false, |r| r.contains(column))
924 /// Adds the bits from row `read` to the bits from row `write`, and
925 /// returns `true` if anything changed.
927 /// This is used when computing transitive reachability because if
928 /// you have an edge `write -> read`, because in that case
929 /// `write` can reach everything that `read` can (and
930 /// potentially more).
931 pub fn union_rows(&mut self, read: R, write: R) -> bool {
932 if read == write || self.row(read).is_none() {
936 self.ensure_row(write);
937 if let (Some(read_row), Some(write_row)) = self.rows.pick2_mut(read, write) {
938 write_row.union(read_row)
944 /// Union a row, `from`, into the `into` row.
945 pub fn union_into_row(&mut self, into: R, from: &HybridBitSet<C>) -> bool {
946 self.ensure_row(into).union(from)
949 /// Insert all bits in the given row.
950 pub fn insert_all_into_row(&mut self, row: R) {
951 self.ensure_row(row).insert_all();
954 pub fn rows(&self) -> impl Iterator<Item = R> {
958 /// Iterates through all the columns set to true in a given row of
960 pub fn iter<'a>(&'a self, row: R) -> impl Iterator<Item = C> + 'a {
961 self.row(row).into_iter().flat_map(|r| r.iter())
964 pub fn row(&self, row: R) -> Option<&HybridBitSet<C>> {
965 if let Some(Some(row)) = self.rows.get(row) {
974 fn num_words<T: Idx>(domain_size: T) -> usize {
975 (domain_size.index() + WORD_BITS - 1) / WORD_BITS
979 fn word_index_and_mask<T: Idx>(elem: T) -> (usize, Word) {
980 let elem = elem.index();
981 let word_index = elem / WORD_BITS;
982 let mask = 1 << (elem % WORD_BITS);