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) {
43 if value != *i { changed = true; }
48 pub fn grow(&mut self, num_bits: usize) {
49 let num_words = u64s(num_bits);
50 let extra_words = self.data.len() - num_words;
51 self.data.extend((0..extra_words).map(|_| 0));
55 /// A "bit matrix" is basically a square matrix of booleans
56 /// represented as one gigantic bitvector. In other words, it is as if
57 /// you have N bitvectors, each of length N. Note that `elements` here is `N`/
59 pub struct BitMatrix {
65 // Create a new `elements x elements` matrix, initially empty.
66 pub fn new(elements: usize) -> BitMatrix {
67 // For every element, we need one bit for every other
68 // element. Round up to an even number of u64s.
69 let u64s_per_elem = u64s(elements);
72 vector: vec![0; elements * u64s_per_elem]
76 /// The range of bits for a given element.
77 fn range(&self, element: usize) -> (usize, usize) {
78 let u64s_per_elem = u64s(self.elements);
79 let start = element * u64s_per_elem;
80 (start, start + u64s_per_elem)
83 pub fn add(&mut self, source: usize, target: usize) -> bool {
84 let (start, _) = self.range(source);
85 let (word, mask) = word_mask(target);
86 let mut vector = &mut self.vector[..];
87 let v1 = vector[start+word];
89 vector[start+word] = v2;
93 /// Do the bits from `source` contain `target`?
95 /// Put another way, if the matrix represents (transitive)
96 /// reachability, can `source` reach `target`?
97 pub fn contains(&self, source: usize, target: usize) -> bool {
98 let (start, _) = self.range(source);
99 let (word, mask) = word_mask(target);
100 (self.vector[start+word] & mask) != 0
103 /// Returns those indices that are reachable from both `a` and
104 /// `b`. This is an O(n) operation where `n` is the number of
105 /// elements (somewhat independent from the actual size of the
106 /// intersection, in particular).
107 pub fn intersection(&self, a: usize, b: usize) -> Vec<usize> {
108 let (a_start, a_end) = self.range(a);
109 let (b_start, b_end) = self.range(b);
110 let mut result = Vec::with_capacity(self.elements);
111 for (base, (i, j)) in (a_start..a_end).zip(b_start..b_end).enumerate() {
112 let mut v = self.vector[i] & self.vector[j];
115 if v & 0x1 != 0 { result.push(base*64 + bit); }
122 /// Add the bits from `read` to the bits from `write`,
123 /// return true if anything changed.
125 /// This is used when computing transitive reachability because if
126 /// you have an edge `write -> read`, because in that case
127 /// `write` can reach everything that `read` can (and
128 /// potentially more).
129 pub fn merge(&mut self, read: usize, write: usize) -> bool {
130 let (read_start, read_end) = self.range(read);
131 let (write_start, write_end) = self.range(write);
132 let vector = &mut self.vector[..];
133 let mut changed = false;
134 for (read_index, write_index) in
135 (read_start..read_end).zip(write_start..write_end)
137 let v1 = vector[write_index];
138 let v2 = v1 | vector[read_index];
139 vector[write_index] = v2;
140 changed = changed | (v1 != v2);
146 fn u64s(elements: usize) -> usize {
150 fn word_mask(index: usize) -> (usize, u64) {
151 let word = index / 64;
152 let mask = 1 << (index % 64);
157 fn union_two_vecs() {
158 let mut vec1 = BitVector::new(65);
159 let mut vec2 = BitVector::new(65);
160 assert!(vec1.insert(3));
161 assert!(!vec1.insert(3));
162 assert!(vec2.insert(5));
163 assert!(vec2.insert(64));
164 assert!(vec1.insert_all(&vec2));
165 assert!(!vec1.insert_all(&vec2));
166 assert!(vec1.contains(3));
167 assert!(!vec1.contains(4));
168 assert!(vec1.contains(5));
169 assert!(!vec1.contains(63));
170 assert!(vec1.contains(64));
175 let mut vec1 = BitVector::new(65);
176 assert!(vec1.insert(3));
177 assert!(!vec1.insert(3));
178 assert!(vec1.insert(5));
179 assert!(vec1.insert(64));
181 assert!(vec1.contains(3));
182 assert!(vec1.contains(5));
183 assert!(vec1.contains(64));
184 assert!(!vec1.contains(126));
188 fn matrix_intersection() {
189 let mut vec1 = BitMatrix::new(200);
191 // (*) Elements reachable from both 2 and 65.
195 vec1.add(2, 10); // (*)
196 vec1.add(2, 64); // (*)
199 vec1.add(2, 160); // (*)
205 vec1.add(65, 10); // (*)
206 vec1.add(65, 64); // (*)
209 vec1.add(65, 160); // (*)
211 let intersection = vec1.intersection(2, 64);
212 assert!(intersection.is_empty());
214 let intersection = vec1.intersection(2, 65);
215 assert_eq!(intersection, &[10, 64, 160]);