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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_LIBARTBASE_BASE_BIT_VECTOR_H_
18 #define ART_LIBARTBASE_BASE_BIT_VECTOR_H_
19 
20 #include <stdint.h>
21 #include <iterator>
22 
23 #include "bit_utils.h"
24 #include "globals.h"
25 
26 namespace art {
27 
28 class Allocator;
29 
30 /*
31  * Expanding bitmap, used for tracking resources.  Bits are numbered starting
32  * from zero.  All operations on a BitVector are unsynchronized.
33  */
34 class BitVector {
35  public:
36   class IndexContainer;
37 
38   /**
39    * @brief Convenient iterator across the indexes of the BitVector's set bits.
40    *
41    * @details IndexIterator is a Forward iterator (C++11: 24.2.5) from the lowest
42    * to the highest index of the BitVector's set bits. Instances can be retrieved
43    * only through BitVector::Indexes() which returns an IndexContainer wrapper
44    * object with begin() and end() suitable for range-based loops:
45    *   for (uint32_t idx : bit_vector.Indexes()) {
46    *     // Use idx.
47    *   }
48    */
49   class IndexIterator :
50       std::iterator<std::forward_iterator_tag, uint32_t, ptrdiff_t, void, uint32_t> {
51    public:
52     bool operator==(const IndexIterator& other) const;
53 
54     bool operator!=(const IndexIterator& other) const {
55       return !(*this == other);
56     }
57 
58     uint32_t operator*() const;
59 
60     IndexIterator& operator++();
61 
62     IndexIterator operator++(int);
63 
64     // Helper function to check for end without comparing with bit_vector.Indexes().end().
Done()65     bool Done() const {
66       return bit_index_ == BitSize();
67     }
68 
69    private:
70     struct begin_tag { };
71     struct end_tag { };
72 
73     IndexIterator(const BitVector* bit_vector, begin_tag);
74     IndexIterator(const BitVector* bit_vector, end_tag);
75 
BitSize()76     uint32_t BitSize() const {
77       return storage_size_ * kWordBits;
78     }
79 
80     uint32_t FindIndex(uint32_t start_index) const;
81     const uint32_t* const bit_storage_;
82     const uint32_t storage_size_;  // Size of vector in words.
83     uint32_t bit_index_;           // Current index (size in bits).
84 
85     friend class BitVector::IndexContainer;
86   };
87 
88   /**
89    * @brief BitVector wrapper class for iteration across indexes of set bits.
90    */
91   class IndexContainer {
92    public:
IndexContainer(const BitVector * bit_vector)93     explicit IndexContainer(const BitVector* bit_vector) : bit_vector_(bit_vector) { }
94 
95     IndexIterator begin() const;
96     IndexIterator end() const;
97 
98    private:
99     const BitVector* const bit_vector_;
100   };
101 
102   // MoveConstructible but not MoveAssignable, CopyConstructible or CopyAssignable.
103 
104   BitVector(const BitVector& other) = delete;
105   BitVector& operator=(const BitVector& other) = delete;
106 
BitVector(BitVector && other)107   BitVector(BitVector&& other)
108       : storage_(other.storage_),
109         storage_size_(other.storage_size_),
110         allocator_(other.allocator_),
111         expandable_(other.expandable_) {
112     other.storage_ = nullptr;
113     other.storage_size_ = 0u;
114   }
115 
116   BitVector(uint32_t start_bits,
117             bool expandable,
118             Allocator* allocator);
119 
120   BitVector(bool expandable,
121             Allocator* allocator,
122             uint32_t storage_size,
123             uint32_t* storage);
124 
125   BitVector(const BitVector& src,
126             bool expandable,
127             Allocator* allocator);
128 
129   virtual ~BitVector();
130 
131   // The number of words necessary to encode bits.
BitsToWords(uint32_t bits)132   static constexpr uint32_t BitsToWords(uint32_t bits) {
133     return RoundUp(bits, kWordBits) / kWordBits;
134   }
135 
136   // Mark the specified bit as "set".
SetBit(uint32_t idx)137   void SetBit(uint32_t idx) {
138     /*
139      * TUNING: this could have pathologically bad growth/expand behavior.  Make sure we're
140      * not using it badly or change resize mechanism.
141      */
142     if (idx >= storage_size_ * kWordBits) {
143       EnsureSize(idx);
144     }
145     storage_[WordIndex(idx)] |= BitMask(idx);
146   }
147 
148   // Mark the specified bit as "unset".
ClearBit(uint32_t idx)149   void ClearBit(uint32_t idx) {
150     // If the index is over the size, we don't have to do anything, it is cleared.
151     if (idx < storage_size_ * kWordBits) {
152       // Otherwise, go ahead and clear it.
153       storage_[WordIndex(idx)] &= ~BitMask(idx);
154     }
155   }
156 
157   // Determine whether or not the specified bit is set.
IsBitSet(uint32_t idx)158   bool IsBitSet(uint32_t idx) const {
159     // If the index is over the size, whether it is expandable or not, this bit does not exist:
160     // thus it is not set.
161     return (idx < (storage_size_ * kWordBits)) && IsBitSet(storage_, idx);
162   }
163 
164   // Mark all bits bit as "clear".
165   void ClearAllBits();
166 
167   // Mark specified number of bits as "set". Cannot set all bits like ClearAll since there might
168   // be unused bits - setting those to one will confuse the iterator.
169   void SetInitialBits(uint32_t num_bits);
170 
171   void Copy(const BitVector* src);
172 
173   // Intersect with another bit vector.
174   void Intersect(const BitVector* src2);
175 
176   // Union with another bit vector.
177   bool Union(const BitVector* src);
178 
179   // Set bits of union_with that are not in not_in.
180   bool UnionIfNotIn(const BitVector* union_with, const BitVector* not_in);
181 
182   void Subtract(const BitVector* src);
183 
184   // Are we equal to another bit vector?  Note: expandability attributes must also match.
185   bool Equal(const BitVector* src) const;
186 
187   /**
188    * @brief Are all the bits set the same?
189    * @details expandability and size can differ as long as the same bits are set.
190    */
191   bool SameBitsSet(const BitVector *src) const;
192 
193   bool IsSubsetOf(const BitVector *other) const;
194 
195   // Count the number of bits that are set.
196   uint32_t NumSetBits() const;
197 
198   // Count the number of bits that are set in range [0, end).
199   uint32_t NumSetBits(uint32_t end) const;
200 
Indexes()201   IndexContainer Indexes() const {
202     return IndexContainer(this);
203   }
204 
GetStorageSize()205   uint32_t GetStorageSize() const {
206     return storage_size_;
207   }
208 
IsExpandable()209   bool IsExpandable() const {
210     return expandable_;
211   }
212 
GetRawStorageWord(size_t idx)213   uint32_t GetRawStorageWord(size_t idx) const {
214     return storage_[idx];
215   }
216 
GetRawStorage()217   uint32_t* GetRawStorage() {
218     return storage_;
219   }
220 
GetRawStorage()221   const uint32_t* GetRawStorage() const {
222     return storage_;
223   }
224 
GetSizeOf()225   size_t GetSizeOf() const {
226     return storage_size_ * kWordBytes;
227   }
228 
229   /**
230    * @return the highest bit set, -1 if none are set
231    */
232   int GetHighestBitSet() const;
233 
234   // Minimum number of bits required to store this vector, 0 if none are set.
GetNumberOfBits()235   size_t GetNumberOfBits() const {
236     return GetHighestBitSet() + 1;
237   }
238 
239   // Is bit set in storage. (No range check.)
IsBitSet(const uint32_t * storage,uint32_t idx)240   static bool IsBitSet(const uint32_t* storage, uint32_t idx) {
241     return (storage[WordIndex(idx)] & BitMask(idx)) != 0;
242   }
243 
244   // Number of bits set in range [0, end) in storage. (No range check.)
245   static uint32_t NumSetBits(const uint32_t* storage, uint32_t end);
246 
247   // Fill given memory region with the contents of the vector and zero padding.
CopyTo(void * dst,size_t len)248   void CopyTo(void* dst, size_t len) const {
249     DCHECK_LE(static_cast<size_t>(GetHighestBitSet() + 1), len * kBitsPerByte);
250     size_t vec_len = GetSizeOf();
251     if (vec_len < len) {
252       void* dst_padding = reinterpret_cast<uint8_t*>(dst) + vec_len;
253       memcpy(dst, storage_, vec_len);
254       memset(dst_padding, 0, len - vec_len);
255     } else {
256       memcpy(dst, storage_, len);
257     }
258   }
259 
260   void Dump(std::ostream& os, const char* prefix) const;
261 
262   Allocator* GetAllocator() const;
263 
264  private:
265   /**
266    * @brief Dump the bitvector into buffer in a 00101..01 format.
267    * @param buffer the ostringstream used to dump the bitvector into.
268    */
269   void DumpHelper(const char* prefix, std::ostringstream& buffer) const;
270 
271   // Ensure there is space for a bit at idx.
272   void EnsureSize(uint32_t idx);
273 
274   // The index of the word within storage.
WordIndex(uint32_t idx)275   static constexpr uint32_t WordIndex(uint32_t idx) {
276     return idx >> 5;
277   }
278 
279   // A bit mask to extract the bit for the given index.
BitMask(uint32_t idx)280   static constexpr uint32_t BitMask(uint32_t idx) {
281     return 1 << (idx & 0x1f);
282   }
283 
284   static constexpr uint32_t kWordBytes = sizeof(uint32_t);
285   static constexpr uint32_t kWordBits = kWordBytes * 8;
286 
287   uint32_t*  storage_;            // The storage for the bit vector.
288   uint32_t   storage_size_;       // Current size, in 32-bit words.
289   Allocator* const allocator_;    // Allocator if expandable.
290   const bool expandable_;         // Should the bitmap expand if too small?
291 };
292 
293 
294 }  // namespace art
295 
296 #endif  // ART_LIBARTBASE_BASE_BIT_VECTOR_H_
297