bit_vector.h revision f10a25f961eb8029c01c84fe8eabd405055cca37
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 "base/bit_utils.h" 24#include "globals.h" 25 26namespace art { 27 28class 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 */ 34class 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(). 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 : bit_storage_(bit_vector->GetRawStorage()), 75 storage_size_(bit_vector->storage_size_), 76 bit_index_(FindIndex(0u)) { } 77 78 IndexIterator(const BitVector* bit_vector, end_tag) 79 : bit_storage_(bit_vector->GetRawStorage()), 80 storage_size_(bit_vector->storage_size_), 81 bit_index_(BitSize()) { } 82 83 uint32_t BitSize() const { 84 return storage_size_ * kWordBits; 85 } 86 87 uint32_t FindIndex(uint32_t start_index) const; 88 const uint32_t* const bit_storage_; 89 const uint32_t storage_size_; // Size of vector in words. 90 uint32_t bit_index_; // Current index (size in bits). 91 92 friend class BitVector::IndexContainer; 93 }; 94 95 /** 96 * @brief BitVector wrapper class for iteration across indexes of set bits. 97 */ 98 class IndexContainer { 99 public: 100 explicit IndexContainer(const BitVector* bit_vector) : bit_vector_(bit_vector) { } 101 102 IndexIterator begin() const { 103 return IndexIterator(bit_vector_, IndexIterator::begin_tag()); 104 } 105 106 IndexIterator end() const { 107 return IndexIterator(bit_vector_, IndexIterator::end_tag()); 108 } 109 110 private: 111 const BitVector* const bit_vector_; 112 }; 113 114 BitVector(uint32_t start_bits, 115 bool expandable, 116 Allocator* allocator, 117 uint32_t storage_size = 0, 118 uint32_t* storage = nullptr); 119 120 virtual ~BitVector(); 121 122 // The number of words necessary to encode bits. 123 static constexpr uint32_t BitsToWords(uint32_t bits) { 124 return RoundUp(bits, kWordBits) / kWordBits; 125 } 126 127 // Mark the specified bit as "set". 128 void SetBit(uint32_t idx) { 129 /* 130 * TUNING: this could have pathologically bad growth/expand behavior. Make sure we're 131 * not using it badly or change resize mechanism. 132 */ 133 if (idx >= storage_size_ * kWordBits) { 134 EnsureSize(idx); 135 } 136 storage_[WordIndex(idx)] |= BitMask(idx); 137 } 138 139 // Mark the specified bit as "unset". 140 void ClearBit(uint32_t idx) { 141 // If the index is over the size, we don't have to do anything, it is cleared. 142 if (idx < storage_size_ * kWordBits) { 143 // Otherwise, go ahead and clear it. 144 storage_[WordIndex(idx)] &= ~BitMask(idx); 145 } 146 } 147 148 // Determine whether or not the specified bit is set. 149 bool IsBitSet(uint32_t idx) const { 150 // If the index is over the size, whether it is expandable or not, this bit does not exist: 151 // thus it is not set. 152 return (idx < (storage_size_ * kWordBits)) && IsBitSet(storage_, idx); 153 } 154 155 // Mark all bits bit as "clear". 156 void ClearAllBits(); 157 158 // Mark specified number of bits as "set". Cannot set all bits like ClearAll since there might 159 // be unused bits - setting those to one will confuse the iterator. 160 void SetInitialBits(uint32_t num_bits); 161 162 void Copy(const BitVector* src); 163 164 // Intersect with another bit vector. 165 void Intersect(const BitVector* src2); 166 167 // Union with another bit vector. 168 bool Union(const BitVector* src); 169 170 // Set bits of union_with that are not in not_in. 171 bool UnionIfNotIn(const BitVector* union_with, const BitVector* not_in); 172 173 void Subtract(const BitVector* src); 174 175 // Are we equal to another bit vector? Note: expandability attributes must also match. 176 bool Equal(const BitVector* src) const; 177 178 /** 179 * @brief Are all the bits set the same? 180 * @details expandability and size can differ as long as the same bits are set. 181 */ 182 bool SameBitsSet(const BitVector *src) const; 183 184 bool IsSubsetOf(const BitVector *other) const; 185 186 // Count the number of bits that are set. 187 uint32_t NumSetBits() const; 188 189 // Count the number of bits that are set in range [0, end). 190 uint32_t NumSetBits(uint32_t end) const; 191 192 IndexContainer Indexes() const { 193 return IndexContainer(this); 194 } 195 196 uint32_t GetStorageSize() const { 197 return storage_size_; 198 } 199 200 bool IsExpandable() const { 201 return expandable_; 202 } 203 204 uint32_t GetRawStorageWord(size_t idx) const { 205 return storage_[idx]; 206 } 207 208 uint32_t* GetRawStorage() { 209 return storage_; 210 } 211 212 const uint32_t* GetRawStorage() const { 213 return storage_; 214 } 215 216 size_t GetSizeOf() const { 217 return storage_size_ * kWordBytes; 218 } 219 220 /** 221 * @return the highest bit set, -1 if none are set 222 */ 223 int GetHighestBitSet() const; 224 225 // Is bit set in storage. (No range check.) 226 static bool IsBitSet(const uint32_t* storage, uint32_t idx) { 227 return (storage[WordIndex(idx)] & BitMask(idx)) != 0; 228 } 229 230 // Number of bits set in range [0, end) in storage. (No range check.) 231 static uint32_t NumSetBits(const uint32_t* storage, uint32_t end); 232 233 // Fill given memory region with the contents of the vector and zero padding. 234 void CopyTo(void* dst, size_t len) const { 235 DCHECK_LE(static_cast<size_t>(GetHighestBitSet() + 1), len * kBitsPerByte); 236 size_t vec_len = GetSizeOf(); 237 if (vec_len < len) { 238 void* dst_padding = reinterpret_cast<uint8_t*>(dst) + vec_len; 239 memcpy(dst, storage_, vec_len); 240 memset(dst_padding, 0, len - vec_len); 241 } else { 242 memcpy(dst, storage_, len); 243 } 244 } 245 246 void Dump(std::ostream& os, const char* prefix) const; 247 248 private: 249 /** 250 * @brief Dump the bitvector into buffer in a 00101..01 format. 251 * @param buffer the ostringstream used to dump the bitvector into. 252 */ 253 void DumpHelper(const char* prefix, std::ostringstream& buffer) const; 254 255 // Ensure there is space for a bit at idx. 256 void EnsureSize(uint32_t idx); 257 258 // The index of the word within storage. 259 static constexpr uint32_t WordIndex(uint32_t idx) { 260 return idx >> 5; 261 } 262 263 // A bit mask to extract the bit for the given index. 264 static constexpr uint32_t BitMask(uint32_t idx) { 265 return 1 << (idx & 0x1f); 266 } 267 268 static constexpr uint32_t kWordBytes = sizeof(uint32_t); 269 static constexpr uint32_t kWordBits = kWordBytes * 8; 270 271 uint32_t* storage_; // The storage for the bit vector. 272 uint32_t storage_size_; // Current size, in 32-bit words. 273 Allocator* const allocator_; // Allocator if expandable. 274 const bool expandable_; // Should the bitmap expand if too small? 275}; 276 277 278} // namespace art 279 280#endif // ART_RUNTIME_BASE_BIT_VECTOR_H_ 281