bit_vector.h revision 920be0b27c72ceb3d40b5f2775cd1950f7c65b5f 
1/*
2 * Copyright (C) 2013 The Android Open Source Project
3 *
4 * Licensed under the Apache License, Version 2.0 (the "License");
5 * you may not use this file except in compliance with the License.
6 * You may obtain a copy of the License at
7 *
8 *      http://www.apache.org/licenses/LICENSE-2.0
9 *
10 * Unless required by applicable law or agreed to in writing, software
11 * distributed under the License is distributed on an "AS IS" BASIS,
12 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
13 * See the License for the specific language governing permissions and
14 * limitations under the License.
15 */
16
17#ifndef ART_RUNTIME_BASE_BIT_VECTOR_H_
18#define ART_RUNTIME_BASE_BIT_VECTOR_H_
19
20#include <stdint.h>
21#include <stddef.h>
22
23#include "allocator.h"
24#include "base/logging.h"
25#include "utils.h"
26
27namespace art {
28
29/*
30 * Expanding bitmap, used for tracking resources.  Bits are numbered starting
31 * from zero.  All operations on a BitVector are unsynchronized.
32 */
33class BitVector {
34  public:
35    class IndexContainer;
36
37    /**
38     * @brief Convenient iterator across the indexes of the BitVector's set bits.
39     *
40     * @details IndexIterator is a Forward iterator (C++11: 24.2.5) from the lowest
41     * to the highest index of the BitVector's set bits. Instances can be retrieved
42     * only through BitVector::Indexes() which returns an IndexContainer wrapper
43     * object with begin() and end() suitable for range-based loops:
44     *   for (uint32_t idx : bit_vector.Indexes()) {
45     *     // Use idx.
46     *   }
47     */
48    class IndexIterator
49        : std::iterator<std::forward_iterator_tag, uint32_t, ptrdiff_t, void, uint32_t> {
50      public:
51        bool operator==(const IndexIterator& other) const {
52          DCHECK(bit_storage_ == other.bit_storage_);
53          DCHECK_EQ(storage_size_, other.storage_size_);
54          return bit_index_ == other.bit_index_;
55        }
56
57        bool operator!=(const IndexIterator& other) const {
58          return !(*this == other);
59        }
60
61        int operator*() const {
62          DCHECK_LT(bit_index_, BitSize());
63          return bit_index_;
64        }
65
66        IndexIterator& operator++() {
67          DCHECK_LT(bit_index_, BitSize());
68          bit_index_ = FindIndex(bit_index_ + 1u);
69          return *this;
70        }
71
72        IndexIterator operator++(int) {
73          IndexIterator result(*this);
74          ++*this;
75          return result;
76        }
77
78        // Helper function to check for end without comparing with bit_vector.Indexes().end().
79        bool Done() const {
80          return bit_index_ == BitSize();
81        }
82
83      private:
84        struct begin_tag { };
85        struct end_tag { };
86
87        IndexIterator(const BitVector* bit_vector, begin_tag)
88          : bit_storage_(bit_vector->GetRawStorage()),
89            storage_size_(bit_vector->storage_size_),
90            bit_index_(FindIndex(0u)) { }
91
92        IndexIterator(const BitVector* bit_vector, end_tag)
93          : bit_storage_(bit_vector->GetRawStorage()),
94            storage_size_(bit_vector->storage_size_),
95            bit_index_(BitSize()) { }
96
97        uint32_t BitSize() const {
98          return storage_size_ * kWordBits;
99        }
100
101        uint32_t FindIndex(uint32_t start_index) const {
102          DCHECK_LE(start_index, BitSize());
103          uint32_t word_index = start_index / kWordBits;
104          if (UNLIKELY(word_index == storage_size_)) {
105            return start_index;
106          }
107          uint32_t word = bit_storage_[word_index];
108          // Mask out any bits in the first word we've already considered.
109          word &= static_cast<uint32_t>(-1) << (start_index & 0x1f);
110          while (word == 0u) {
111            ++word_index;
112            if (UNLIKELY(word_index == storage_size_)) {
113              return BitSize();
114            }
115            word = bit_storage_[word_index];
116          }
117          return word_index * 32u + CTZ(word);
118        }
119
120        const uint32_t* const bit_storage_;
121        const uint32_t storage_size_;  // Size of vector in words.
122        uint32_t bit_index_;           // Current index (size in bits).
123
124        friend class BitVector::IndexContainer;
125    };
126
127    /**
128     * @brief BitVector wrapper class for iteration across indexes of set bits.
129     */
130    class IndexContainer {
131     public:
132      explicit IndexContainer(const BitVector* bit_vector) : bit_vector_(bit_vector) { }
133
134      IndexIterator begin() const {
135        return IndexIterator(bit_vector_, IndexIterator::begin_tag());
136      }
137
138      IndexIterator end() const {
139        return IndexIterator(bit_vector_, IndexIterator::end_tag());
140      }
141
142     private:
143      const BitVector* const bit_vector_;
144    };
145
146    BitVector(uint32_t start_bits,
147              bool expandable,
148              Allocator* allocator,
149              uint32_t storage_size = 0,
150              uint32_t* storage = nullptr);
151
152    virtual ~BitVector();
153
154    void SetBit(uint32_t num);
155    void ClearBit(uint32_t num);
156    bool IsBitSet(uint32_t num) const;
157    void ClearAllBits();
158    void SetInitialBits(uint32_t num_bits);
159
160    void Copy(const BitVector* src);
161    void Intersect(const BitVector* src2);
162    bool Union(const BitVector* src);
163
164    // Set bits of union_with that are not in not_in.
165    bool UnionIfNotIn(const BitVector* union_with, const BitVector* not_in);
166
167    void Subtract(const BitVector* src);
168    // Are we equal to another bit vector?  Note: expandability attributes must also match.
169    bool Equal(const BitVector* src) {
170      return (storage_size_ == src->GetStorageSize()) &&
171        (expandable_ == src->IsExpandable()) &&
172        (memcmp(storage_, src->GetRawStorage(), storage_size_ * sizeof(uint32_t)) == 0);
173    }
174
175    /**
176     * @brief Are all the bits set the same?
177     * @details expandability and size can differ as long as the same bits are set.
178     */
179    bool SameBitsSet(const BitVector *src);
180
181    uint32_t NumSetBits() const;
182
183    // Number of bits set in range [0, end).
184    uint32_t NumSetBits(uint32_t end) const;
185
186    IndexContainer Indexes() const {
187      return IndexContainer(this);
188    }
189
190    uint32_t GetStorageSize() const { return storage_size_; }
191    bool IsExpandable() const { return expandable_; }
192    uint32_t GetRawStorageWord(size_t idx) const { return storage_[idx]; }
193    uint32_t* GetRawStorage() { return storage_; }
194    const uint32_t* GetRawStorage() const { return storage_; }
195    size_t GetSizeOf() const { return storage_size_ * kWordBytes; }
196
197    /**
198     * @return the highest bit set, -1 if none are set
199     */
200    int GetHighestBitSet() const;
201
202    // Is bit set in storage. (No range check.)
203    static bool IsBitSet(const uint32_t* storage, uint32_t num);
204    // Number of bits set in range [0, end) in storage. (No range check.)
205    static uint32_t NumSetBits(const uint32_t* storage, uint32_t end);
206
207    bool EnsureSizeAndClear(unsigned int num);
208
209    void Dump(std::ostream& os, const char* prefix) const;
210    void DumpDot(FILE* file, const char* prefix, bool last_entry = false) const;
211
212  protected:
213    void DumpHelper(std::ostringstream& buffer, const char* prefix) const;
214
215  private:
216    static constexpr uint32_t kWordBytes = sizeof(uint32_t);
217    static constexpr uint32_t kWordBits = kWordBytes * 8;
218
219    Allocator* const allocator_;
220    const bool expandable_;         // expand bitmap if we run out?
221    uint32_t   storage_size_;       // current size, in 32-bit words.
222    uint32_t*  storage_;
223    uint32_t number_of_bits_;
224};
225
226
227}  // namespace art
228
229#endif  // ART_RUNTIME_BASE_BIT_VECTOR_H_
230