bit_vector.h revision 8db2a6deb82d9c14d62e7ea201bc27b3040f1b62
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 <iterator> 22 23#include "utils.h" 24 25namespace art { 26 27class Allocator; 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 53 bool operator!=(const IndexIterator& other) const { 54 return !(*this == other); 55 } 56 57 uint32_t operator*() const; 58 59 IndexIterator& operator++(); 60 61 IndexIterator operator++(int); 62 63 // Helper function to check for end without comparing with bit_vector.Indexes().end(). 64 bool Done() const { 65 return bit_index_ == BitSize(); 66 } 67 68 private: 69 struct begin_tag { }; 70 struct end_tag { }; 71 72 IndexIterator(const BitVector* bit_vector, begin_tag) 73 : bit_storage_(bit_vector->GetRawStorage()), 74 storage_size_(bit_vector->storage_size_), 75 bit_index_(FindIndex(0u)) { } 76 77 IndexIterator(const BitVector* bit_vector, end_tag) 78 : bit_storage_(bit_vector->GetRawStorage()), 79 storage_size_(bit_vector->storage_size_), 80 bit_index_(BitSize()) { } 81 82 uint32_t BitSize() const { 83 return storage_size_ * kWordBits; 84 } 85 86 uint32_t FindIndex(uint32_t start_index) const; 87 const uint32_t* const bit_storage_; 88 const uint32_t storage_size_; // Size of vector in words. 89 uint32_t bit_index_; // Current index (size in bits). 90 91 friend class BitVector::IndexContainer; 92 }; 93 94 /** 95 * @brief BitVector wrapper class for iteration across indexes of set bits. 96 */ 97 class IndexContainer { 98 public: 99 explicit IndexContainer(const BitVector* bit_vector) : bit_vector_(bit_vector) { } 100 101 IndexIterator begin() const { 102 return IndexIterator(bit_vector_, IndexIterator::begin_tag()); 103 } 104 105 IndexIterator end() const { 106 return IndexIterator(bit_vector_, IndexIterator::end_tag()); 107 } 108 109 private: 110 const BitVector* const bit_vector_; 111 }; 112 113 BitVector(uint32_t start_bits, 114 bool expandable, 115 Allocator* allocator, 116 uint32_t storage_size = 0, 117 uint32_t* storage = nullptr); 118 119 virtual ~BitVector(); 120 121 // The number of words necessary to encode bits. 122 static constexpr uint32_t BitsToWords(uint32_t bits) { 123 return RoundUp(bits, kWordBits) / kWordBits; 124 } 125 126 // Mark the specified bit as "set". 127 void SetBit(uint32_t idx) { 128 /* 129 * TUNING: this could have pathologically bad growth/expand behavior. Make sure we're 130 * not using it badly or change resize mechanism. 131 */ 132 if (idx >= storage_size_ * kWordBits) { 133 EnsureSize(idx); 134 } 135 storage_[WordIndex(idx)] |= BitMask(idx); 136 } 137 138 // Mark the specified bit as "unset". 139 void ClearBit(uint32_t idx) { 140 // If the index is over the size, we don't have to do anything, it is cleared. 141 if (idx < storage_size_ * kWordBits) { 142 // Otherwise, go ahead and clear it. 143 storage_[WordIndex(idx)] &= ~BitMask(idx); 144 } 145 } 146 147 // Determine whether or not the specified bit is set. 148 bool IsBitSet(uint32_t idx) const { 149 // If the index is over the size, whether it is expandable or not, this bit does not exist: 150 // thus it is not set. 151 return (idx < (storage_size_ * kWordBits)) && IsBitSet(storage_, idx); 152 } 153 154 // Mark all bits bit as "clear". 155 void ClearAllBits(); 156 157 // Mark specified number of bits as "set". Cannot set all bits like ClearAll since there might 158 // be unused bits - setting those to one will confuse the iterator. 159 void SetInitialBits(uint32_t num_bits); 160 161 void Copy(const BitVector* src); 162 163 // Intersect with another bit vector. 164 void Intersect(const BitVector* src2); 165 166 // Union with another bit vector. 167 bool Union(const BitVector* src); 168 169 // Set bits of union_with that are not in not_in. 170 bool UnionIfNotIn(const BitVector* union_with, const BitVector* not_in); 171 172 void Subtract(const BitVector* src); 173 174 // Are we equal to another bit vector? Note: expandability attributes must also match. 175 bool Equal(const BitVector* src) const; 176 177 /** 178 * @brief Are all the bits set the same? 179 * @details expandability and size can differ as long as the same bits are set. 180 */ 181 bool SameBitsSet(const BitVector *src) const; 182 183 bool IsSubsetOf(const BitVector *other) const; 184 185 // Count the number of bits that are set. 186 uint32_t NumSetBits() const; 187 188 // Count the number of bits that are set in range [0, end). 189 uint32_t NumSetBits(uint32_t end) const; 190 191 IndexContainer Indexes() const { 192 return IndexContainer(this); 193 } 194 195 uint32_t GetStorageSize() const { 196 return storage_size_; 197 } 198 199 bool IsExpandable() const { 200 return expandable_; 201 } 202 203 uint32_t GetRawStorageWord(size_t idx) const { 204 return storage_[idx]; 205 } 206 207 uint32_t* GetRawStorage() { 208 return storage_; 209 } 210 211 const uint32_t* GetRawStorage() const { 212 return storage_; 213 } 214 215 size_t GetSizeOf() const { 216 return storage_size_ * kWordBytes; 217 } 218 219 /** 220 * @return the highest bit set, -1 if none are set 221 */ 222 int GetHighestBitSet() const; 223 224 // Is bit set in storage. (No range check.) 225 static bool IsBitSet(const uint32_t* storage, uint32_t idx) { 226 return (storage[WordIndex(idx)] & BitMask(idx)) != 0; 227 } 228 229 // Number of bits set in range [0, end) in storage. (No range check.) 230 static uint32_t NumSetBits(const uint32_t* storage, uint32_t end); 231 232 void Dump(std::ostream& os, const char* prefix) const; 233 234 private: 235 /** 236 * @brief Dump the bitvector into buffer in a 00101..01 format. 237 * @param buffer the ostringstream used to dump the bitvector into. 238 */ 239 void DumpHelper(const char* prefix, std::ostringstream& buffer) const; 240 241 // Ensure there is space for a bit at idx. 242 void EnsureSize(uint32_t idx); 243 244 // The index of the word within storage. 245 static constexpr uint32_t WordIndex(uint32_t idx) { 246 return idx >> 5; 247 } 248 249 // A bit mask to extract the bit for the given index. 250 static constexpr uint32_t BitMask(uint32_t idx) { 251 return 1 << (idx & 0x1f); 252 } 253 254 static constexpr uint32_t kWordBytes = sizeof(uint32_t); 255 static constexpr uint32_t kWordBits = kWordBytes * 8; 256 257 uint32_t* storage_; // The storage for the bit vector. 258 uint32_t storage_size_; // Current size, in 32-bit words. 259 Allocator* const allocator_; // Allocator if expandable. 260 const bool expandable_; // Should the bitmap expand if too small? 261}; 262 263 264} // namespace art 265 266#endif // ART_RUNTIME_BASE_BIT_VECTOR_H_ 267