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* Copyright (C) 2013 The Android Open Source Project
* Licensed under the Apache License, Version 2.0 (the "License");
* you may not use this file except in compliance with the License.
* You may obtain a copy of the License at
* Unless required by applicable law or agreed to in writing, software
* distributed under the License is distributed on an "AS IS" BASIS,
* See the License for the specific language governing permissions and
* limitations under the License.
#include <stdint.h>
#include <iterator>
#include "base/bit_utils.h"
#include "globals.h"
namespace art {
class Allocator;
* Expanding bitmap, used for tracking resources. Bits are numbered starting
* from zero. All operations on a BitVector are unsynchronized.
class BitVector {
class IndexContainer;
* @brief Convenient iterator across the indexes of the BitVector's set bits.
* @details IndexIterator is a Forward iterator (C++11: 24.2.5) from the lowest
* to the highest index of the BitVector's set bits. Instances can be retrieved
* only through BitVector::Indexes() which returns an IndexContainer wrapper
* object with begin() and end() suitable for range-based loops:
* for (uint32_t idx : bit_vector.Indexes()) {
* // Use idx.
* }
class IndexIterator :
std::iterator<std::forward_iterator_tag, uint32_t, ptrdiff_t, void, uint32_t> {
bool operator==(const IndexIterator& other) const;
bool operator!=(const IndexIterator& other) const {
return !(*this == other);
uint32_t operator*() const;
IndexIterator& operator++();
IndexIterator operator++(int);
// Helper function to check for end without comparing with bit_vector.Indexes().end().
bool Done() const {
return bit_index_ == BitSize();
struct begin_tag { };
struct end_tag { };
IndexIterator(const BitVector* bit_vector, begin_tag)
: bit_storage_(bit_vector->GetRawStorage()),
bit_index_(FindIndex(0u)) { }
IndexIterator(const BitVector* bit_vector, end_tag)
: bit_storage_(bit_vector->GetRawStorage()),
bit_index_(BitSize()) { }
uint32_t BitSize() const {
return storage_size_ * kWordBits;
uint32_t FindIndex(uint32_t start_index) const;
const uint32_t* const bit_storage_;
const uint32_t storage_size_; // Size of vector in words.
uint32_t bit_index_; // Current index (size in bits).
friend class BitVector::IndexContainer;
* @brief BitVector wrapper class for iteration across indexes of set bits.
class IndexContainer {
explicit IndexContainer(const BitVector* bit_vector) : bit_vector_(bit_vector) { }
IndexIterator begin() const {
return IndexIterator(bit_vector_, IndexIterator::begin_tag());
IndexIterator end() const {
return IndexIterator(bit_vector_, IndexIterator::end_tag());
const BitVector* const bit_vector_;
BitVector(uint32_t start_bits,
bool expandable,
Allocator* allocator);
BitVector(bool expandable,
Allocator* allocator,
uint32_t storage_size,
uint32_t* storage);
BitVector(const BitVector& src,
bool expandable,
Allocator* allocator);
virtual ~BitVector();
// The number of words necessary to encode bits.
static constexpr uint32_t BitsToWords(uint32_t bits) {
return RoundUp(bits, kWordBits) / kWordBits;
// Mark the specified bit as "set".
void SetBit(uint32_t idx) {
* TUNING: this could have pathologically bad growth/expand behavior. Make sure we're
* not using it badly or change resize mechanism.
if (idx >= storage_size_ * kWordBits) {
storage_[WordIndex(idx)] |= BitMask(idx);
// Mark the specified bit as "unset".
void ClearBit(uint32_t idx) {
// If the index is over the size, we don't have to do anything, it is cleared.
if (idx < storage_size_ * kWordBits) {
// Otherwise, go ahead and clear it.
storage_[WordIndex(idx)] &= ~BitMask(idx);
// Determine whether or not the specified bit is set.
bool IsBitSet(uint32_t idx) const {
// If the index is over the size, whether it is expandable or not, this bit does not exist:
// thus it is not set.
return (idx < (storage_size_ * kWordBits)) && IsBitSet(storage_, idx);
// Mark all bits bit as "clear".
void ClearAllBits();
// Mark specified number of bits as "set". Cannot set all bits like ClearAll since there might
// be unused bits - setting those to one will confuse the iterator.
void SetInitialBits(uint32_t num_bits);
void Copy(const BitVector* src);
// Intersect with another bit vector.
void Intersect(const BitVector* src2);
// Union with another bit vector.
bool Union(const BitVector* src);
// Set bits of union_with that are not in not_in.
bool UnionIfNotIn(const BitVector* union_with, const BitVector* not_in);
void Subtract(const BitVector* src);
// Are we equal to another bit vector? Note: expandability attributes must also match.
bool Equal(const BitVector* src) const;
* @brief Are all the bits set the same?
* @details expandability and size can differ as long as the same bits are set.
bool SameBitsSet(const BitVector *src) const;
bool IsSubsetOf(const BitVector *other) const;
// Count the number of bits that are set.
uint32_t NumSetBits() const;
// Count the number of bits that are set in range [0, end).
uint32_t NumSetBits(uint32_t end) const;
IndexContainer Indexes() const {
return IndexContainer(this);
uint32_t GetStorageSize() const {
return storage_size_;
bool IsExpandable() const {
return expandable_;
uint32_t GetRawStorageWord(size_t idx) const {
return storage_[idx];
uint32_t* GetRawStorage() {
return storage_;
const uint32_t* GetRawStorage() const {
return storage_;
size_t GetSizeOf() const {
return storage_size_ * kWordBytes;
* @return the highest bit set, -1 if none are set
int GetHighestBitSet() const;
// Is bit set in storage. (No range check.)
static bool IsBitSet(const uint32_t* storage, uint32_t idx) {
return (storage[WordIndex(idx)] & BitMask(idx)) != 0;
// Number of bits set in range [0, end) in storage. (No range check.)
static uint32_t NumSetBits(const uint32_t* storage, uint32_t end);
// Fill given memory region with the contents of the vector and zero padding.
void CopyTo(void* dst, size_t len) const {
DCHECK_LE(static_cast<size_t>(GetHighestBitSet() + 1), len * kBitsPerByte);
size_t vec_len = GetSizeOf();
if (vec_len < len) {
void* dst_padding = reinterpret_cast<uint8_t*>(dst) + vec_len;
memcpy(dst, storage_, vec_len);
memset(dst_padding, 0, len - vec_len);
} else {
memcpy(dst, storage_, len);
void Dump(std::ostream& os, const char* prefix) const;
Allocator* GetAllocator() const;
* @brief Dump the bitvector into buffer in a 00101..01 format.
* @param buffer the ostringstream used to dump the bitvector into.
void DumpHelper(const char* prefix, std::ostringstream& buffer) const;
// Ensure there is space for a bit at idx.
void EnsureSize(uint32_t idx);
// The index of the word within storage.
static constexpr uint32_t WordIndex(uint32_t idx) {
return idx >> 5;
// A bit mask to extract the bit for the given index.
static constexpr uint32_t BitMask(uint32_t idx) {
return 1 << (idx & 0x1f);
static constexpr uint32_t kWordBytes = sizeof(uint32_t);
static constexpr uint32_t kWordBits = kWordBytes * 8;
uint32_t* storage_; // The storage for the bit vector.
uint32_t storage_size_; // Current size, in 32-bit words.
Allocator* const allocator_; // Allocator if expandable.
const bool expandable_; // Should the bitmap expand if too small?
} // namespace art