1 // Copyright 2015 The Rust Project Developers. See the COPYRIGHT
2 // file at the top-level directory of this distribution and at
3 // http://rust-lang.org/COPYRIGHT.
5 // Licensed under the Apache License, Version 2.0 <LICENSE-APACHE or
6 // http://www.apache.org/licenses/LICENSE-2.0> or the MIT license
7 // <LICENSE-MIT or http://opensource.org/licenses/MIT>, at your
8 // option. This file may not be copied, modified, or distributed
9 // except according to those terms.
11 /// A very simple BitVector type.
12 pub struct BitVector {
17 pub fn new(num_bits: usize) -> BitVector {
18 let num_words = u64s(num_bits);
19 BitVector { data: vec![0; num_words] }
22 pub fn contains(&self, bit: usize) -> bool {
23 let (word, mask) = word_mask(bit);
24 (self.data[word] & mask) != 0
27 /// Returns true if the bit has changed.
28 pub fn insert(&mut self, bit: usize) -> bool {
29 let (word, mask) = word_mask(bit);
30 let data = &mut self.data[word];
32 let new_value = value | mask;
37 pub fn insert_all(&mut self, all: &BitVector) -> bool {
38 assert!(self.data.len() == all.data.len());
39 let mut changed = false;
40 for (i, j) in self.data.iter_mut().zip(&all.data) {
50 pub fn grow(&mut self, num_bits: usize) {
51 let num_words = u64s(num_bits);
52 let extra_words = self.data.len() - num_words;
53 self.data.extend((0..extra_words).map(|_| 0));
56 /// Iterates over indexes of set bits in a sorted order
57 pub fn iter<'a>(&'a self) -> BitVectorIter<'a> {
59 iter: self.data.iter(),
66 pub struct BitVectorIter<'a> {
67 iter: ::std::slice::Iter<'a, u64>,
72 impl<'a> Iterator for BitVectorIter<'a> {
74 fn next(&mut self) -> Option<usize> {
75 while self.current == 0 {
76 self.current = if let Some(&i) = self.iter.next() {
81 self.idx = u64s(self.idx) * 64;
88 let offset = self.current.trailing_zeros() as usize;
89 self.current >>= offset;
90 self.current >>= 1; // shift otherwise overflows for 0b1000_0000_…_0000
91 self.idx += offset + 1;
92 return Some(self.idx - 1);
96 /// A "bit matrix" is basically a square matrix of booleans
97 /// represented as one gigantic bitvector. In other words, it is as if
98 /// you have N bitvectors, each of length N. Note that `elements` here is `N`/
100 pub struct BitMatrix {
106 // Create a new `elements x elements` matrix, initially empty.
107 pub fn new(elements: usize) -> BitMatrix {
108 // For every element, we need one bit for every other
109 // element. Round up to an even number of u64s.
110 let u64s_per_elem = u64s(elements);
113 vector: vec![0; elements * u64s_per_elem],
117 /// The range of bits for a given element.
118 fn range(&self, element: usize) -> (usize, usize) {
119 let u64s_per_elem = u64s(self.elements);
120 let start = element * u64s_per_elem;
121 (start, start + u64s_per_elem)
124 pub fn add(&mut self, source: usize, target: usize) -> bool {
125 let (start, _) = self.range(source);
126 let (word, mask) = word_mask(target);
127 let mut vector = &mut self.vector[..];
128 let v1 = vector[start + word];
130 vector[start + word] = v2;
134 /// Do the bits from `source` contain `target`?
136 /// Put another way, if the matrix represents (transitive)
137 /// reachability, can `source` reach `target`?
138 pub fn contains(&self, source: usize, target: usize) -> bool {
139 let (start, _) = self.range(source);
140 let (word, mask) = word_mask(target);
141 (self.vector[start + word] & mask) != 0
144 /// Returns those indices that are reachable from both `a` and
145 /// `b`. This is an O(n) operation where `n` is the number of
146 /// elements (somewhat independent from the actual size of the
147 /// intersection, in particular).
148 pub fn intersection(&self, a: usize, b: usize) -> Vec<usize> {
149 let (a_start, a_end) = self.range(a);
150 let (b_start, b_end) = self.range(b);
151 let mut result = Vec::with_capacity(self.elements);
152 for (base, (i, j)) in (a_start..a_end).zip(b_start..b_end).enumerate() {
153 let mut v = self.vector[i] & self.vector[j];
159 result.push(base * 64 + bit);
167 /// Add the bits from `read` to the bits from `write`,
168 /// return true if anything changed.
170 /// This is used when computing transitive reachability because if
171 /// you have an edge `write -> read`, because in that case
172 /// `write` can reach everything that `read` can (and
173 /// potentially more).
174 pub fn merge(&mut self, read: usize, write: usize) -> bool {
175 let (read_start, read_end) = self.range(read);
176 let (write_start, write_end) = self.range(write);
177 let vector = &mut self.vector[..];
178 let mut changed = false;
179 for (read_index, write_index) in (read_start..read_end).zip(write_start..write_end) {
180 let v1 = vector[write_index];
181 let v2 = v1 | vector[read_index];
182 vector[write_index] = v2;
183 changed = changed | (v1 != v2);
189 fn u64s(elements: usize) -> usize {
193 fn word_mask(index: usize) -> (usize, u64) {
194 let word = index / 64;
195 let mask = 1 << (index % 64);
200 fn bitvec_iter_works() {
201 let mut bitvec = BitVector::new(100);
211 assert_eq!(bitvec.iter().collect::<Vec<_>>(),
212 [1, 10, 19, 62, 63, 64, 65, 66, 99]);
216 fn bitvec_iter_works_2() {
217 let mut bitvec = BitVector::new(300);
225 assert_eq!(bitvec.iter().collect::<Vec<_>>(),
226 [1, 10, 19, 62, 66, 99, 299]);
231 fn bitvec_iter_works_3() {
232 let mut bitvec = BitVector::new(319);
238 assert_eq!(bitvec.iter().collect::<Vec<_>>(), [0, 127, 191, 255, 319]);
242 fn union_two_vecs() {
243 let mut vec1 = BitVector::new(65);
244 let mut vec2 = BitVector::new(65);
245 assert!(vec1.insert(3));
246 assert!(!vec1.insert(3));
247 assert!(vec2.insert(5));
248 assert!(vec2.insert(64));
249 assert!(vec1.insert_all(&vec2));
250 assert!(!vec1.insert_all(&vec2));
251 assert!(vec1.contains(3));
252 assert!(!vec1.contains(4));
253 assert!(vec1.contains(5));
254 assert!(!vec1.contains(63));
255 assert!(vec1.contains(64));
260 let mut vec1 = BitVector::new(65);
261 assert!(vec1.insert(3));
262 assert!(!vec1.insert(3));
263 assert!(vec1.insert(5));
264 assert!(vec1.insert(64));
266 assert!(vec1.contains(3));
267 assert!(vec1.contains(5));
268 assert!(vec1.contains(64));
269 assert!(!vec1.contains(126));
273 fn matrix_intersection() {
274 let mut vec1 = BitMatrix::new(200);
276 // (*) Elements reachable from both 2 and 65.
280 vec1.add(2, 10); // (*)
281 vec1.add(2, 64); // (*)
284 vec1.add(2, 160); // (*)
290 vec1.add(65, 10); // (*)
291 vec1.add(65, 64); // (*)
294 vec1.add(65, 160); // (*)
296 let intersection = vec1.intersection(2, 64);
297 assert!(intersection.is_empty());
299 let intersection = vec1.intersection(2, 65);
300 assert_eq!(intersection, &[10, 64, 160]);