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/*
* Copyright (C) 2017 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
*
* http://www.apache.org/licenses/LICENSE-2.0
*
* Unless required by applicable law or agreed to in writing, software
* distributed under the License is distributed on an "AS IS" BASIS,
* WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
* See the License for the specific language governing permissions and
* limitations under the License.
*/
#ifndef ART_LIBARTBASE_BASE_BIT_MEMORY_REGION_H_
#define ART_LIBARTBASE_BASE_BIT_MEMORY_REGION_H_
#include "memory_region.h"
#include "bit_utils.h"
#include "memory_tool.h"
#include <array>
namespace art {
// Bit memory region is a bit offset subregion of a normal memoryregion. This is useful for
// abstracting away the bit start offset to avoid needing passing as an argument everywhere.
class BitMemoryRegion final : public ValueObject {
public:
struct Less {
bool operator()(const BitMemoryRegion& lhs, const BitMemoryRegion& rhs) const {
return Compare(lhs, rhs) < 0;
}
};
BitMemoryRegion() = default;
ALWAYS_INLINE BitMemoryRegion(uint8_t* data, ssize_t bit_start, size_t bit_size) {
// Normalize the data pointer. Note that bit_start may be negative.
data_ = AlignDown(data + (bit_start >> kBitsPerByteLog2), kPageSize);
bit_start_ = bit_start + kBitsPerByte * (data - data_);
bit_size_ = bit_size;
}
ALWAYS_INLINE explicit BitMemoryRegion(MemoryRegion region)
: BitMemoryRegion(region.begin(), /* bit_start */ 0, region.size_in_bits()) {
}
ALWAYS_INLINE BitMemoryRegion(MemoryRegion region, size_t bit_offset, size_t bit_length)
: BitMemoryRegion(region) {
*this = Subregion(bit_offset, bit_length);
}
ALWAYS_INLINE bool IsValid() const { return data_ != nullptr; }
const uint8_t* data() const {
DCHECK_ALIGNED(bit_start_, kBitsPerByte);
return data_ + bit_start_ / kBitsPerByte;
}
size_t size_in_bits() const {
return bit_size_;
}
void Resize(size_t bit_size) {
bit_size_ = bit_size;
}
ALWAYS_INLINE BitMemoryRegion Subregion(size_t bit_offset, size_t bit_length) const {
DCHECK_LE(bit_offset, bit_size_);
DCHECK_LE(bit_length, bit_size_ - bit_offset);
BitMemoryRegion result = *this;
result.bit_start_ += bit_offset;
result.bit_size_ = bit_length;
return result;
}
ALWAYS_INLINE BitMemoryRegion Subregion(size_t bit_offset) const {
DCHECK_LE(bit_offset, bit_size_);
BitMemoryRegion result = *this;
result.bit_start_ += bit_offset;
result.bit_size_ -= bit_offset;
return result;
}
// Load a single bit in the region. The bit at offset 0 is the least
// significant bit in the first byte.
ALWAYS_INLINE bool LoadBit(size_t bit_offset) const {
DCHECK_LT(bit_offset, bit_size_);
size_t index = (bit_start_ + bit_offset) / kBitsPerByte;
size_t shift = (bit_start_ + bit_offset) % kBitsPerByte;
return ((data_[index] >> shift) & 1) != 0;
}
ALWAYS_INLINE void StoreBit(size_t bit_offset, bool value) {
DCHECK_LT(bit_offset, bit_size_);
size_t index = (bit_start_ + bit_offset) / kBitsPerByte;
size_t shift = (bit_start_ + bit_offset) % kBitsPerByte;
data_[index] &= ~(1 << shift); // Clear bit.
data_[index] |= (value ? 1 : 0) << shift; // Set bit.
DCHECK_EQ(value, LoadBit(bit_offset));
}
// Load `bit_length` bits from `data` starting at given `bit_offset`.
// The least significant bit is stored in the smallest memory offset.
template<typename Result = size_t>
ATTRIBUTE_NO_SANITIZE_ADDRESS // We might touch extra bytes due to the alignment.
ALWAYS_INLINE Result LoadBits(size_t bit_offset, size_t bit_length) const {
static_assert(std::is_integral<Result>::value, "Result must be integral");
static_assert(std::is_unsigned<Result>::value, "Result must be unsigned");
DCHECK(IsAligned<sizeof(Result)>(data_));
DCHECK_LE(bit_offset, bit_size_);
DCHECK_LE(bit_length, bit_size_ - bit_offset);
DCHECK_LE(bit_length, BitSizeOf<Result>());
if (bit_length == 0) {
return 0;
}
// Load naturally-aligned value which contains the least significant bit.
Result* data = reinterpret_cast<Result*>(data_);
size_t width = BitSizeOf<Result>();
size_t index = (bit_start_ + bit_offset) / width;
size_t shift = (bit_start_ + bit_offset) % width;
Result value = data[index] >> shift;
// Load extra value containing the most significant bit (it might be the same one).
// We can not just load the following value as that could potentially cause SIGSEGV.
Result extra = data[index + (shift + (bit_length - 1)) / width];
// Mask to clear unwanted bits (the 1s are needed to avoid avoid undefined shift).
Result clear = (std::numeric_limits<Result>::max() << 1) << (bit_length - 1);
// Prepend the extra value. We add explicit '& (width - 1)' so that the shift is defined.
// It is a no-op for `shift != 0` and if `shift == 0` then `value == extra` because of
// bit_length <= width causing the `value` and `extra` to be read from the same location.
// The '& (width - 1)' is implied by the shift instruction on ARM and removed by compiler.
return (value | (extra << ((width - shift) & (width - 1)))) & ~clear;
}
// Store `bit_length` bits in `data` starting at given `bit_offset`.
// The least significant bit is stored in the smallest memory offset.
ALWAYS_INLINE void StoreBits(size_t bit_offset, uint32_t value, size_t bit_length) {
DCHECK_LE(bit_offset, bit_size_);
DCHECK_LE(bit_length, bit_size_ - bit_offset);
DCHECK_LE(bit_length, BitSizeOf<uint32_t>());
DCHECK_LE(value, MaxInt<uint32_t>(bit_length));
if (bit_length == 0) {
return;
}
// Write data byte by byte to avoid races with other threads
// on bytes that do not overlap with this region.
uint32_t mask = std::numeric_limits<uint32_t>::max() >> (BitSizeOf<uint32_t>() - bit_length);
size_t index = (bit_start_ + bit_offset) / kBitsPerByte;
size_t shift = (bit_start_ + bit_offset) % kBitsPerByte;
data_[index] &= ~(mask << shift); // Clear bits.
data_[index] |= (value << shift); // Set bits.
size_t finished_bits = kBitsPerByte - shift;
for (int i = 1; finished_bits < bit_length; i++, finished_bits += kBitsPerByte) {
data_[index + i] &= ~(mask >> finished_bits); // Clear bits.
data_[index + i] |= (value >> finished_bits); // Set bits.
}
DCHECK_EQ(value, LoadBits(bit_offset, bit_length));
}
// Store bits from other bit region.
ALWAYS_INLINE void StoreBits(size_t bit_offset, const BitMemoryRegion& src, size_t bit_length) {
DCHECK_LE(bit_offset, bit_size_);
DCHECK_LE(bit_length, bit_size_ - bit_offset);
size_t bit = 0;
constexpr size_t kNumBits = BitSizeOf<uint32_t>();
for (; bit + kNumBits <= bit_length; bit += kNumBits) {
StoreBits(bit_offset + bit, src.LoadBits(bit, kNumBits), kNumBits);
}
size_t num_bits = bit_length - bit;
StoreBits(bit_offset + bit, src.LoadBits(bit, num_bits), num_bits);
}
// Count the number of set bits within the given bit range.
ALWAYS_INLINE size_t PopCount(size_t bit_offset, size_t bit_length) const {
DCHECK_LE(bit_offset, bit_size_);
DCHECK_LE(bit_length, bit_size_ - bit_offset);
size_t count = 0;
size_t bit = 0;
constexpr size_t kNumBits = BitSizeOf<uint32_t>();
for (; bit + kNumBits <= bit_length; bit += kNumBits) {
count += POPCOUNT(LoadBits(bit_offset + bit, kNumBits));
}
count += POPCOUNT(LoadBits(bit_offset + bit, bit_length - bit));
return count;
}
static int Compare(const BitMemoryRegion& lhs, const BitMemoryRegion& rhs) {
if (lhs.size_in_bits() != rhs.size_in_bits()) {
return (lhs.size_in_bits() < rhs.size_in_bits()) ? -1 : 1;
}
size_t bit = 0;
constexpr size_t kNumBits = BitSizeOf<uint32_t>();
for (; bit + kNumBits <= lhs.size_in_bits(); bit += kNumBits) {
uint32_t lhs_bits = lhs.LoadBits(bit, kNumBits);
uint32_t rhs_bits = rhs.LoadBits(bit, kNumBits);
if (lhs_bits != rhs_bits) {
return (lhs_bits < rhs_bits) ? -1 : 1;
}
}
size_t num_bits = lhs.size_in_bits() - bit;
uint32_t lhs_bits = lhs.LoadBits(bit, num_bits);
uint32_t rhs_bits = rhs.LoadBits(bit, num_bits);
if (lhs_bits != rhs_bits) {
return (lhs_bits < rhs_bits) ? -1 : 1;
}
return 0;
}
private:
uint8_t* data_ = nullptr; // The pointer is page aligned.
size_t bit_start_ = 0;
size_t bit_size_ = 0;
};
constexpr uint32_t kVarintBits = 4; // Minimum number of bits used for varint.
constexpr uint32_t kVarintMax = 11; // Maximum value which is stored "inline".
class BitMemoryReader {
public:
BitMemoryReader(BitMemoryReader&&) = default;
explicit BitMemoryReader(BitMemoryRegion data)
: finished_region_(data.Subregion(0, 0) /* set the length to zero */ ) {
}
explicit BitMemoryReader(const uint8_t* data, ssize_t bit_offset = 0)
: finished_region_(const_cast<uint8_t*>(data), bit_offset, /* bit_length */ 0) {
}
const uint8_t* data() const { return finished_region_.data(); }
BitMemoryRegion GetReadRegion() const { return finished_region_; }
size_t NumberOfReadBits() const { return finished_region_.size_in_bits(); }
ALWAYS_INLINE BitMemoryRegion ReadRegion(size_t bit_length) {
size_t bit_offset = finished_region_.size_in_bits();
finished_region_.Resize(bit_offset + bit_length);
return finished_region_.Subregion(bit_offset, bit_length);
}
template<typename Result = size_t>
ALWAYS_INLINE Result ReadBits(size_t bit_length) {
return ReadRegion(bit_length).LoadBits<Result>(/* bit_offset */ 0, bit_length);
}
ALWAYS_INLINE bool ReadBit() {
return ReadRegion(/* bit_length */ 1).LoadBit(/* bit_offset */ 0);
}
// Read variable-length bit-packed integer.
// The first four bits determine the variable length of the encoded integer:
// Values 0..11 represent the result as-is, with no further following bits.
// Values 12..15 mean the result is in the next 8/16/24/32-bits respectively.
ALWAYS_INLINE uint32_t ReadVarint() {
uint32_t x = ReadBits(kVarintBits);
return (x <= kVarintMax) ? x : ReadBits((x - kVarintMax) * kBitsPerByte);
}
// Read N 'interleaved' varints (different to just reading consecutive varints).
// All small values are stored first and the large values are stored after them.
// This requires fewer bit-reads compared to indidually storing the varints.
template<size_t N>
ALWAYS_INLINE std::array<uint32_t, N> ReadInterleavedVarints() {
static_assert(N * kVarintBits <= sizeof(uint64_t) * kBitsPerByte, "N too big");
std::array<uint32_t, N> values;
// StackMap BitTable uses over 8 varints in the header, so we need uint64_t.
uint64_t data = ReadBits<uint64_t>(N * kVarintBits);
for (size_t i = 0; i < N; i++) {
values[i] = BitFieldExtract(data, i * kVarintBits, kVarintBits);
}
// Do the second part in its own loop as that seems to produce better code in clang.
for (size_t i = 0; i < N; i++) {
if (UNLIKELY(values[i] > kVarintMax)) {
values[i] = ReadBits((values[i] - kVarintMax) * kBitsPerByte);
}
}
return values;
}
private:
// Represents all of the bits which were read so far. There is no upper bound.
// Therefore, by definition, the "cursor" is always at the end of the region.
BitMemoryRegion finished_region_;
DISALLOW_COPY_AND_ASSIGN(BitMemoryReader);
};
template<typename Vector>
class BitMemoryWriter {
public:
explicit BitMemoryWriter(Vector* out, size_t bit_offset = 0)
: out_(out), bit_start_(bit_offset), bit_offset_(bit_offset) {
DCHECK_EQ(NumberOfWrittenBits(), 0u);
}
BitMemoryRegion GetWrittenRegion() const {
return BitMemoryRegion(out_->data(), bit_start_, bit_offset_ - bit_start_);
}
const uint8_t* data() const { return out_->data(); }
size_t NumberOfWrittenBits() const { return bit_offset_ - bit_start_; }
ALWAYS_INLINE BitMemoryRegion Allocate(size_t bit_length) {
out_->resize(BitsToBytesRoundUp(bit_offset_ + bit_length));
BitMemoryRegion region(out_->data(), bit_offset_, bit_length);
DCHECK_LE(bit_length, std::numeric_limits<size_t>::max() - bit_offset_) << "Overflow";
bit_offset_ += bit_length;
return region;
}
ALWAYS_INLINE void WriteRegion(const BitMemoryRegion& region) {
Allocate(region.size_in_bits()).StoreBits(/* bit_offset */ 0, region, region.size_in_bits());
}
ALWAYS_INLINE void WriteBits(uint32_t value, size_t bit_length) {
Allocate(bit_length).StoreBits(/* bit_offset */ 0, value, bit_length);
}
ALWAYS_INLINE void WriteBit(bool value) {
Allocate(1).StoreBit(/* bit_offset */ 0, value);
}
template<size_t N>
ALWAYS_INLINE void WriteInterleavedVarints(std::array<uint32_t, N> values) {
// Write small values (or the number of bytes needed for the large values).
for (uint32_t value : values) {
if (value > kVarintMax) {
WriteBits(kVarintMax + BitsToBytesRoundUp(MinimumBitsToStore(value)), kVarintBits);
} else {
WriteBits(value, kVarintBits);
}
}
// Write large values.
for (uint32_t value : values) {
if (value > kVarintMax) {
WriteBits(value, BitsToBytesRoundUp(MinimumBitsToStore(value)) * kBitsPerByte);
}
}
}
ALWAYS_INLINE void WriteVarint(uint32_t value) {
WriteInterleavedVarints<1>({value});
}
ALWAYS_INLINE void ByteAlign() {
size_t end = bit_start_ + bit_offset_;
bit_offset_ += RoundUp(end, kBitsPerByte) - end;
}
private:
Vector* out_;
size_t bit_start_;
size_t bit_offset_;
DISALLOW_COPY_AND_ASSIGN(BitMemoryWriter);
};
} // namespace art
#endif // ART_LIBARTBASE_BASE_BIT_MEMORY_REGION_H_