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> {
171 BitIter::new(&self.words)
174 /// Duplicates the set as a hybrid set.
175 pub fn to_hybrid(&self) -> HybridBitSet<T> {
176 // Note: we currently don't bother trying to make a Sparse set.
177 HybridBitSet::Dense(self.to_owned())
180 /// Set `self = self | other`. In contrast to `union` returns `true` if the set contains at
181 /// least one bit that is not in `other` (i.e. `other` is not a superset of `self`).
183 /// This is an optimization for union of a hybrid bitset.
184 fn reverse_union_sparse(&mut self, sparse: &SparseBitSet<T>) -> bool {
185 assert!(sparse.domain_size == self.domain_size);
186 self.clear_excess_bits();
188 let mut not_already = false;
189 // Index of the current word not yet merged.
190 let mut current_index = 0;
191 // Mask of bits that came from the sparse set in the current word.
192 let mut new_bit_mask = 0;
193 for (word_index, mask) in sparse.iter().map(|x| word_index_and_mask(*x)) {
194 // Next bit is in a word not inspected yet.
195 if word_index > current_index {
196 self.words[current_index] |= new_bit_mask;
197 // Were there any bits in the old word that did not occur in the sparse set?
198 not_already |= (self.words[current_index] ^ new_bit_mask) != 0;
199 // Check all words we skipped for any set bit.
200 not_already |= self.words[current_index+1..word_index].iter().any(|&x| x != 0);
202 current_index = word_index;
203 // Reset bit mask, no bits have been merged yet.
206 // Add bit and mark it as coming from the sparse set.
207 // self.words[word_index] |= mask;
208 new_bit_mask |= mask;
210 self.words[current_index] |= new_bit_mask;
211 // Any bits in the last inspected word that were not in the sparse set?
212 not_already |= (self.words[current_index] ^ new_bit_mask) != 0;
213 // Any bits in the tail? Note `clear_excess_bits` before.
214 not_already |= self.words[current_index+1..].iter().any(|&x| x != 0);
220 /// This is implemented by all the bitsets so that BitSet::union() can be
221 /// passed any type of bitset.
222 pub trait UnionIntoBitSet<T: Idx> {
223 // Performs `other = other | self`.
224 fn union_into(&self, other: &mut BitSet<T>) -> bool;
227 /// This is implemented by all the bitsets so that BitSet::subtract() can be
228 /// passed any type of bitset.
229 pub trait SubtractFromBitSet<T: Idx> {
230 // Performs `other = other - self`.
231 fn subtract_from(&self, other: &mut BitSet<T>) -> bool;
234 impl<T: Idx> UnionIntoBitSet<T> for BitSet<T> {
235 fn union_into(&self, other: &mut BitSet<T>) -> bool {
236 assert_eq!(self.domain_size, other.domain_size);
237 bitwise(&mut other.words, &self.words, |a, b| { a | b })
241 impl<T: Idx> SubtractFromBitSet<T> for BitSet<T> {
242 fn subtract_from(&self, other: &mut BitSet<T>) -> bool {
243 assert_eq!(self.domain_size, other.domain_size);
244 bitwise(&mut other.words, &self.words, |a, b| { a & !b })
248 impl<T: Idx> fmt::Debug for BitSet<T> {
249 fn fmt(&self, w: &mut fmt::Formatter<'_>) -> fmt::Result {
251 .entries(self.iter())
256 impl<T: Idx> ToString for BitSet<T> {
257 fn to_string(&self) -> String {
258 let mut result = String::new();
261 // Note: this is a little endian printout of bytes.
263 // i tracks how many bits we have printed so far.
265 for word in &self.words {
266 let mut word = *word;
267 for _ in 0..WORD_BYTES { // for each byte in `word`:
268 let remain = self.domain_size - i;
269 // If less than a byte remains, then mask just that many bits.
270 let mask = if remain <= 8 { (1 << remain) - 1 } else { 0xFF };
271 assert!(mask <= 0xFF);
272 let byte = word & mask;
274 result.push_str(&format!("{}{:02x}", sep, byte));
276 if remain <= 8 { break; }
289 pub struct BitIter<'a, T: Idx> {
290 cur: Option<(Word, usize)>,
291 iter: iter::Enumerate<slice::Iter<'a, Word>>,
292 marker: PhantomData<T>
295 impl<'a, T: Idx> BitIter<'a, T> {
297 fn new(words: &'a [Word]) -> BitIter<'a, T> {
300 iter: words.iter().enumerate(),
306 impl<'a, T: Idx> Iterator for BitIter<'a, T> {
308 fn next(&mut self) -> Option<T> {
310 if let Some((ref mut word, offset)) = self.cur {
311 let bit_pos = word.trailing_zeros() as usize;
312 if bit_pos != WORD_BITS {
313 let bit = 1 << bit_pos;
315 return Some(T::new(bit_pos + offset))
319 let (i, word) = self.iter.next()?;
320 self.cur = Some((*word, WORD_BITS * i));
326 fn bitwise<Op>(out_vec: &mut [Word], in_vec: &[Word], op: Op) -> bool
327 where Op: Fn(Word, Word) -> Word
329 assert_eq!(out_vec.len(), in_vec.len());
330 let mut changed = false;
331 for (out_elem, in_elem) in out_vec.iter_mut().zip(in_vec.iter()) {
332 let old_val = *out_elem;
333 let new_val = op(old_val, *in_elem);
335 changed |= old_val != new_val;
340 const SPARSE_MAX: usize = 8;
342 /// A fixed-size bitset type with a sparse representation and a maximum of
343 /// `SPARSE_MAX` elements. The elements are stored as a sorted `SmallVec` with
344 /// no duplicates; although `SmallVec` can spill its elements to the heap, that
345 /// never happens within this type because of the `SPARSE_MAX` limit.
347 /// This type is used by `HybridBitSet`; do not use directly.
348 #[derive(Clone, Debug)]
349 pub struct SparseBitSet<T: Idx> {
351 elems: SmallVec<[T; SPARSE_MAX]>,
354 impl<T: Idx> SparseBitSet<T> {
355 fn new_empty(domain_size: usize) -> Self {
358 elems: SmallVec::new()
362 fn len(&self) -> usize {
366 fn is_empty(&self) -> bool {
367 self.elems.len() == 0
370 fn contains(&self, elem: T) -> bool {
371 assert!(elem.index() < self.domain_size);
372 self.elems.contains(&elem)
375 fn insert(&mut self, elem: T) -> bool {
376 assert!(elem.index() < self.domain_size);
377 let changed = if let Some(i) = self.elems.iter().position(|&e| e >= elem) {
378 if self.elems[i] == elem {
379 // `elem` is already in the set.
382 // `elem` is smaller than one or more existing elements.
383 self.elems.insert(i, elem);
387 // `elem` is larger than all existing elements.
388 self.elems.push(elem);
391 assert!(self.len() <= SPARSE_MAX);
395 fn remove(&mut self, elem: T) -> bool {
396 assert!(elem.index() < self.domain_size);
397 if let Some(i) = self.elems.iter().position(|&e| e == elem) {
398 self.elems.remove(i);
405 fn to_dense(&self) -> BitSet<T> {
406 let mut dense = BitSet::new_empty(self.domain_size);
407 for elem in self.elems.iter() {
413 fn iter(&self) -> slice::Iter<'_, T> {
418 impl<T: Idx> UnionIntoBitSet<T> for SparseBitSet<T> {
419 fn union_into(&self, other: &mut BitSet<T>) -> bool {
420 assert_eq!(self.domain_size, other.domain_size);
421 let mut changed = false;
422 for elem in self.iter() {
423 changed |= other.insert(*elem);
429 impl<T: Idx> SubtractFromBitSet<T> for SparseBitSet<T> {
430 fn subtract_from(&self, other: &mut BitSet<T>) -> bool {
431 assert_eq!(self.domain_size, other.domain_size);
432 let mut changed = false;
433 for elem in self.iter() {
434 changed |= other.remove(*elem);
440 /// A fixed-size bitset type with a hybrid representation: sparse when there
441 /// are up to a `SPARSE_MAX` elements in the set, but dense when there are more
442 /// than `SPARSE_MAX`.
444 /// This type is especially efficient for sets that typically have a small
445 /// number of elements, but a large `domain_size`, and are cleared frequently.
447 /// `T` is an index type, typically a newtyped `usize` wrapper, but it can also
450 /// All operations that involve an element will panic if the element is equal
451 /// to or greater than the domain size. All operations that involve two bitsets
452 /// will panic if the bitsets have differing domain sizes.
453 #[derive(Clone, Debug)]
454 pub enum HybridBitSet<T: Idx> {
455 Sparse(SparseBitSet<T>),
459 impl<T: Idx> HybridBitSet<T> {
460 pub fn new_empty(domain_size: usize) -> Self {
461 HybridBitSet::Sparse(SparseBitSet::new_empty(domain_size))
464 fn domain_size(&self) -> usize {
466 HybridBitSet::Sparse(sparse) => sparse.domain_size,
467 HybridBitSet::Dense(dense) => dense.domain_size,
471 pub fn clear(&mut self) {
472 let domain_size = self.domain_size();
473 *self = HybridBitSet::new_empty(domain_size);
476 pub fn contains(&self, elem: T) -> bool {
478 HybridBitSet::Sparse(sparse) => sparse.contains(elem),
479 HybridBitSet::Dense(dense) => dense.contains(elem),
483 pub fn superset(&self, other: &HybridBitSet<T>) -> bool {
484 match (self, other) {
485 (HybridBitSet::Dense(self_dense), HybridBitSet::Dense(other_dense)) => {
486 self_dense.superset(other_dense)
489 assert!(self.domain_size() == other.domain_size());
490 other.iter().all(|elem| self.contains(elem))
495 pub fn is_empty(&self) -> bool {
497 HybridBitSet::Sparse(sparse) => sparse.is_empty(),
498 HybridBitSet::Dense(dense) => dense.is_empty(),
502 pub fn insert(&mut self, elem: T) -> bool {
503 // No need to check `elem` against `self.domain_size` here because all
504 // the match cases check it, one way or another.
506 HybridBitSet::Sparse(sparse) if sparse.len() < SPARSE_MAX => {
507 // The set is sparse and has space for `elem`.
510 HybridBitSet::Sparse(sparse) if sparse.contains(elem) => {
511 // The set is sparse and does not have space for `elem`, but
512 // that doesn't matter because `elem` is already present.
515 HybridBitSet::Sparse(sparse) => {
516 // The set is sparse and full. Convert to a dense set.
517 let mut dense = sparse.to_dense();
518 let changed = dense.insert(elem);
520 *self = HybridBitSet::Dense(dense);
523 HybridBitSet::Dense(dense) => dense.insert(elem),
527 pub fn insert_all(&mut self) {
528 let domain_size = self.domain_size();
530 HybridBitSet::Sparse(_) => {
531 *self = HybridBitSet::Dense(BitSet::new_filled(domain_size));
533 HybridBitSet::Dense(dense) => dense.insert_all(),
537 pub fn remove(&mut self, elem: T) -> bool {
538 // Note: we currently don't bother going from Dense back to Sparse.
540 HybridBitSet::Sparse(sparse) => sparse.remove(elem),
541 HybridBitSet::Dense(dense) => dense.remove(elem),
545 pub fn union(&mut self, other: &HybridBitSet<T>) -> bool {
547 HybridBitSet::Sparse(self_sparse) => {
549 HybridBitSet::Sparse(other_sparse) => {
550 // Both sets are sparse. Add the elements in
551 // `other_sparse` to `self` one at a time. This
552 // may or may not cause `self` to be densified.
553 assert_eq!(self.domain_size(), other.domain_size());
554 let mut changed = false;
555 for elem in other_sparse.iter() {
556 changed |= self.insert(*elem);
560 HybridBitSet::Dense(other_dense) => {
561 // `self` is sparse and `other` is dense. To
562 // merge them, we have two available strategies:
563 // * Densify `self` then merge other
564 // * Clone other then integrate bits from `self`
565 // The second strategy requires dedicated method
566 // since the usual `union` returns the wrong
567 // result. In the dedicated case the computation
568 // is slightly faster if the bits of the sparse
569 // bitset map to only few words of the dense
570 // representation, i.e. indices are near each
573 // Benchmarking seems to suggest that the second
574 // option is worth it.
575 let mut new_dense = other_dense.clone();
576 let changed = new_dense.reverse_union_sparse(self_sparse);
577 *self = HybridBitSet::Dense(new_dense);
583 HybridBitSet::Dense(self_dense) => self_dense.union(other),
587 /// Converts to a dense set, consuming itself in the process.
588 pub fn to_dense(self) -> BitSet<T> {
590 HybridBitSet::Sparse(sparse) => sparse.to_dense(),
591 HybridBitSet::Dense(dense) => dense,
595 pub fn iter(&self) -> HybridIter<'_, T> {
597 HybridBitSet::Sparse(sparse) => HybridIter::Sparse(sparse.iter()),
598 HybridBitSet::Dense(dense) => HybridIter::Dense(dense.iter()),
603 impl<T: Idx> UnionIntoBitSet<T> for HybridBitSet<T> {
604 fn union_into(&self, other: &mut BitSet<T>) -> bool {
606 HybridBitSet::Sparse(sparse) => sparse.union_into(other),
607 HybridBitSet::Dense(dense) => dense.union_into(other),
612 impl<T: Idx> SubtractFromBitSet<T> for HybridBitSet<T> {
613 fn subtract_from(&self, other: &mut BitSet<T>) -> bool {
615 HybridBitSet::Sparse(sparse) => sparse.subtract_from(other),
616 HybridBitSet::Dense(dense) => dense.subtract_from(other),
621 pub enum HybridIter<'a, T: Idx> {
622 Sparse(slice::Iter<'a, T>),
623 Dense(BitIter<'a, T>),
626 impl<'a, T: Idx> Iterator for HybridIter<'a, T> {
629 fn next(&mut self) -> Option<T> {
631 HybridIter::Sparse(sparse) => sparse.next().copied(),
632 HybridIter::Dense(dense) => dense.next(),
637 /// A resizable bitset type with a dense representation.
639 /// `T` is an index type, typically a newtyped `usize` wrapper, but it can also
642 /// All operations that involve an element will panic if the element is equal
643 /// to or greater than the domain size.
644 #[derive(Clone, Debug, PartialEq)]
645 pub struct GrowableBitSet<T: Idx> {
649 impl<T: Idx> GrowableBitSet<T> {
650 /// Ensure that the set can hold at least `min_domain_size` elements.
651 pub fn ensure(&mut self, min_domain_size: usize) {
652 if self.bit_set.domain_size < min_domain_size {
653 self.bit_set.domain_size = min_domain_size;
656 let min_num_words = num_words(min_domain_size);
657 if self.bit_set.words.len() < min_num_words {
658 self.bit_set.words.resize(min_num_words, 0)
662 pub fn new_empty() -> GrowableBitSet<T> {
663 GrowableBitSet { bit_set: BitSet::new_empty(0) }
666 pub fn with_capacity(capacity: usize) -> GrowableBitSet<T> {
667 GrowableBitSet { bit_set: BitSet::new_empty(capacity) }
670 /// Returns `true` if the set has changed.
672 pub fn insert(&mut self, elem: T) -> bool {
673 self.ensure(elem.index() + 1);
674 self.bit_set.insert(elem)
678 pub fn contains(&self, elem: T) -> bool {
679 let (word_index, mask) = word_index_and_mask(elem);
680 if let Some(word) = self.bit_set.words.get(word_index) {
688 /// A fixed-size 2D bit matrix type with a dense representation.
690 /// `R` and `C` are index types used to identify rows and columns respectively;
691 /// typically newtyped `usize` wrappers, but they can also just be `usize`.
693 /// All operations that involve a row and/or column index will panic if the
694 /// index exceeds the relevant bound.
695 #[derive(Clone, Debug, Eq, PartialEq, RustcDecodable, RustcEncodable)]
696 pub struct BitMatrix<R: Idx, C: Idx> {
700 marker: PhantomData<(R, C)>,
703 impl<R: Idx, C: Idx> BitMatrix<R, C> {
704 /// Creates a new `rows x columns` matrix, initially empty.
705 pub fn new(num_rows: usize, num_columns: usize) -> BitMatrix<R, C> {
706 // For every element, we need one bit for every other
707 // element. Round up to an even number of words.
708 let words_per_row = num_words(num_columns);
712 words: vec![0; num_rows * words_per_row],
717 /// Creates a new matrix, with `row` used as the value for every row.
718 pub fn from_row_n(row: &BitSet<C>, num_rows: usize) -> BitMatrix<R, C> {
719 let num_columns = row.domain_size();
720 let words_per_row = num_words(num_columns);
721 assert_eq!(words_per_row, row.words().len());
725 words: iter::repeat(row.words()).take(num_rows).flatten().cloned().collect(),
730 pub fn rows(&self) -> impl Iterator<Item = R> {
731 (0..self.num_rows).map(R::new)
734 /// The range of bits for a given row.
735 fn range(&self, row: R) -> (usize, usize) {
736 let words_per_row = num_words(self.num_columns);
737 let start = row.index() * words_per_row;
738 (start, start + words_per_row)
741 /// Sets the cell at `(row, column)` to true. Put another way, insert
742 /// `column` to the bitset for `row`.
744 /// Returns `true` if this changed the matrix.
745 pub fn insert(&mut self, row: R, column: C) -> bool {
746 assert!(row.index() < self.num_rows && column.index() < self.num_columns);
747 let (start, _) = self.range(row);
748 let (word_index, mask) = word_index_and_mask(column);
749 let words = &mut self.words[..];
750 let word = words[start + word_index];
751 let new_word = word | mask;
752 words[start + word_index] = new_word;
756 /// Do the bits from `row` contain `column`? Put another way, is
757 /// the matrix cell at `(row, column)` true? Put yet another way,
758 /// if the matrix represents (transitive) reachability, can
759 /// `row` reach `column`?
760 pub fn contains(&self, row: R, column: C) -> bool {
761 assert!(row.index() < self.num_rows && column.index() < self.num_columns);
762 let (start, _) = self.range(row);
763 let (word_index, mask) = word_index_and_mask(column);
764 (self.words[start + word_index] & mask) != 0
767 /// Returns those indices that are true in rows `a` and `b`. This
768 /// is an O(n) operation where `n` is the number of elements
769 /// (somewhat independent from the actual size of the
770 /// intersection, in particular).
771 pub fn intersect_rows(&self, row1: R, row2: R) -> Vec<C> {
772 assert!(row1.index() < self.num_rows && row2.index() < self.num_rows);
773 let (row1_start, row1_end) = self.range(row1);
774 let (row2_start, row2_end) = self.range(row2);
775 let mut result = Vec::with_capacity(self.num_columns);
776 for (base, (i, j)) in (row1_start..row1_end).zip(row2_start..row2_end).enumerate() {
777 let mut v = self.words[i] & self.words[j];
778 for bit in 0..WORD_BITS {
783 result.push(C::new(base * WORD_BITS + bit));
791 /// Adds the bits from row `read` to the bits from row `write`, and
792 /// returns `true` if anything changed.
794 /// This is used when computing transitive reachability because if
795 /// you have an edge `write -> read`, because in that case
796 /// `write` can reach everything that `read` can (and
797 /// potentially more).
798 pub fn union_rows(&mut self, read: R, write: R) -> bool {
799 assert!(read.index() < self.num_rows && write.index() < self.num_rows);
800 let (read_start, read_end) = self.range(read);
801 let (write_start, write_end) = self.range(write);
802 let words = &mut self.words[..];
803 let mut changed = false;
804 for (read_index, write_index) in (read_start..read_end).zip(write_start..write_end) {
805 let word = words[write_index];
806 let new_word = word | words[read_index];
807 words[write_index] = new_word;
808 changed |= word != new_word;
813 /// Adds the bits from `with` to the bits from row `write`, and
814 /// returns `true` if anything changed.
815 pub fn union_row_with(&mut self, with: &BitSet<C>, write: R) -> bool {
816 assert!(write.index() < self.num_rows);
817 assert_eq!(with.domain_size(), self.num_columns);
818 let (write_start, write_end) = self.range(write);
819 let mut changed = false;
820 for (read_index, write_index) in (0..with.words().len()).zip(write_start..write_end) {
821 let word = self.words[write_index];
822 let new_word = word | with.words()[read_index];
823 self.words[write_index] = new_word;
824 changed |= word != new_word;
829 /// Sets every cell in `row` to true.
830 pub fn insert_all_into_row(&mut self, row: R) {
831 assert!(row.index() < self.num_rows);
832 let (start, end) = self.range(row);
833 let words = &mut self.words[..];
834 for index in start..end {
837 self.clear_excess_bits(row);
840 /// Clear excess bits in the final word of the row.
841 fn clear_excess_bits(&mut self, row: R) {
842 let num_bits_in_final_word = self.num_columns % WORD_BITS;
843 if num_bits_in_final_word > 0 {
844 let mask = (1 << num_bits_in_final_word) - 1;
845 let (_, end) = self.range(row);
846 let final_word_idx = end - 1;
847 self.words[final_word_idx] &= mask;
851 /// Gets a slice of the underlying words.
852 pub fn words(&self) -> &[Word] {
856 /// Iterates through all the columns set to true in a given row of
858 pub fn iter(&self, row: R) -> BitIter<'_, C> {
859 assert!(row.index() < self.num_rows);
860 let (start, end) = self.range(row);
861 BitIter::new(&self.words[start..end])
864 /// Returns the number of elements in `row`.
865 pub fn count(&self, row: R) -> usize {
866 let (start, end) = self.range(row);
867 self.words[start..end].iter().map(|e| e.count_ones() as usize).sum()
871 /// A fixed-column-size, variable-row-size 2D bit matrix with a moderately
872 /// sparse representation.
874 /// Initially, every row has no explicit representation. If any bit within a
875 /// row is set, the entire row is instantiated as `Some(<HybridBitSet>)`.
876 /// Furthermore, any previously uninstantiated rows prior to it will be
877 /// instantiated as `None`. Those prior rows may themselves become fully
878 /// instantiated later on if any of their bits are set.
880 /// `R` and `C` are index types used to identify rows and columns respectively;
881 /// typically newtyped `usize` wrappers, but they can also just be `usize`.
882 #[derive(Clone, Debug)]
883 pub struct SparseBitMatrix<R, C>
889 rows: IndexVec<R, Option<HybridBitSet<C>>>,
892 impl<R: Idx, C: Idx> SparseBitMatrix<R, C> {
893 /// Creates a new empty sparse bit matrix with no rows or columns.
894 pub fn new(num_columns: usize) -> Self {
897 rows: IndexVec::new(),
901 fn ensure_row(&mut self, row: R) -> &mut HybridBitSet<C> {
902 // Instantiate any missing rows up to and including row `row` with an
903 // empty HybridBitSet.
904 self.rows.ensure_contains_elem(row, || None);
906 // Then replace row `row` with a full HybridBitSet if necessary.
907 let num_columns = self.num_columns;
908 self.rows[row].get_or_insert_with(|| HybridBitSet::new_empty(num_columns))
911 /// Sets the cell at `(row, column)` to true. Put another way, insert
912 /// `column` to the bitset for `row`.
914 /// Returns `true` if this changed the matrix.
915 pub fn insert(&mut self, row: R, column: C) -> bool {
916 self.ensure_row(row).insert(column)
919 /// Do the bits from `row` contain `column`? Put another way, is
920 /// the matrix cell at `(row, column)` true? Put yet another way,
921 /// if the matrix represents (transitive) reachability, can
922 /// `row` reach `column`?
923 pub fn contains(&self, row: R, column: C) -> bool {
924 self.row(row).map_or(false, |r| r.contains(column))
927 /// Adds the bits from row `read` to the bits from row `write`, and
928 /// returns `true` if anything changed.
930 /// This is used when computing transitive reachability because if
931 /// you have an edge `write -> read`, because in that case
932 /// `write` can reach everything that `read` can (and
933 /// potentially more).
934 pub fn union_rows(&mut self, read: R, write: R) -> bool {
935 if read == write || self.row(read).is_none() {
939 self.ensure_row(write);
940 if let (Some(read_row), Some(write_row)) = self.rows.pick2_mut(read, write) {
941 write_row.union(read_row)
947 /// Union a row, `from`, into the `into` row.
948 pub fn union_into_row(&mut self, into: R, from: &HybridBitSet<C>) -> bool {
949 self.ensure_row(into).union(from)
952 /// Insert all bits in the given row.
953 pub fn insert_all_into_row(&mut self, row: R) {
954 self.ensure_row(row).insert_all();
957 pub fn rows(&self) -> impl Iterator<Item = R> {
961 /// Iterates through all the columns set to true in a given row of
963 pub fn iter<'a>(&'a self, row: R) -> impl Iterator<Item = C> + 'a {
964 self.row(row).into_iter().flat_map(|r| r.iter())
967 pub fn row(&self, row: R) -> Option<&HybridBitSet<C>> {
968 if let Some(Some(row)) = self.rows.get(row) {
977 fn num_words<T: Idx>(domain_size: T) -> usize {
978 (domain_size.index() + WORD_BITS - 1) / WORD_BITS
982 fn word_index_and_mask<T: Idx>(elem: T) -> (usize, Word) {
983 let elem = elem.index();
984 let word_index = elem / WORD_BITS;
985 let mask = 1 << (elem % WORD_BITS);