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// Copyright (c) the JPEG XL Project Authors. All rights reserved.
//
// Use of this source code is governed by a BSD-style
// license that can be found in the LICENSE file.
#ifndef LIB_JXL_BASE_PADDED_BYTES_H_
#define LIB_JXL_BASE_PADDED_BYTES_H_
// std::vector replacement with padding to reduce bounds checks in WriteBits
#include <jxl/memory_manager.h>
#include <algorithm> // max
#include <cstddef>
#include <cstdint>
#include <cstring> // memcpy
#include <initializer_list>
#include <utility> // swap
#include "lib/jxl/base/status.h"
#include "lib/jxl/memory_manager_internal.h"
namespace jxl {
// Provides a subset of the std::vector interface with some differences:
// - allows BitWriter to write 64 bits at a time without bounds checking;
// - ONLY zero-initializes the first byte (required by BitWriter);
// - ensures cache-line alignment.
class PaddedBytes {
public:
// Required for output params.
explicit PaddedBytes(JxlMemoryManager* memory_manager)
: memory_manager_(memory_manager), size_(0), capacity_(0) {}
static StatusOr<PaddedBytes> WithInitialSpace(
JxlMemoryManager* memory_manager, size_t size) {
PaddedBytes result(memory_manager);
JXL_RETURN_IF_ERROR(result.Init(size));
return result;
}
// Deleting copy constructor and copy assignment operator to prevent copying
PaddedBytes(const PaddedBytes&) = delete;
PaddedBytes& operator=(const PaddedBytes&) = delete;
// default is not OK - need to set other.size_ to 0!
PaddedBytes(PaddedBytes&& other) noexcept
: memory_manager_(other.memory_manager_),
size_(other.size_),
capacity_(other.capacity_),
data_(std::move(other.data_)) {
other.size_ = other.capacity_ = 0;
}
PaddedBytes& operator=(PaddedBytes&& other) noexcept {
memory_manager_ = other.memory_manager_;
size_ = other.size_;
capacity_ = other.capacity_;
data_ = std::move(other.data_);
if (&other != this) {
other.size_ = other.capacity_ = 0;
}
return *this;
}
JxlMemoryManager* memory_manager() const { return memory_manager_; }
void swap(PaddedBytes& other) noexcept {
std::swap(memory_manager_, other.memory_manager_);
std::swap(size_, other.size_);
std::swap(capacity_, other.capacity_);
std::swap(data_, other.data_);
}
// If current capacity is greater than requested, then no-op. Otherwise
// copies existing data to newly allocated "data_".
// The new capacity will be at least 1.5 times the old capacity. This ensures
// that we avoid quadratic behaviour.
Status reserve(size_t capacity) {
if (capacity <= capacity_) return true;
size_t new_capacity = std::max(capacity, 3 * capacity_ / 2);
new_capacity = std::max<size_t>(64, new_capacity);
// BitWriter writes up to 7 bytes past the end.
JXL_ASSIGN_OR_RETURN(
AlignedMemory new_data,
AlignedMemory::Create(memory_manager_, new_capacity + 8));
if (data_.address<void>() == nullptr) {
// First allocation: ensure first byte is initialized (won't be copied).
new_data.address<uint8_t>()[0] = 0;
} else {
// Subsequent resize: copy existing data to new location.
memmove(new_data.address<void>(), data_.address<void>(), size_);
// Ensure that the first new byte is initialized, to allow write_bits to
// safely append to the newly-resized PaddedBytes.
new_data.address<uint8_t>()[size_] = 0;
}
capacity_ = new_capacity;
data_ = std::move(new_data);
return true;
}
// NOTE: unlike vector, this does not initialize the new data!
// However, we guarantee that write_bits can safely append after
// the resize, as we zero-initialize the first new byte of data.
// If size < capacity(), does not invalidate the memory.
Status resize(size_t size) {
JXL_RETURN_IF_ERROR(reserve(size));
size_ = size;
return true;
}
// resize(size) plus explicit initialization of the new data with `value`.
Status resize(size_t size, uint8_t value) {
size_t old_size = size_;
JXL_RETURN_IF_ERROR(resize(size));
if (size_ > old_size) {
memset(data() + old_size, value, size_ - old_size);
}
return true;
}
// Amortized constant complexity due to exponential growth.
Status push_back(uint8_t x) {
if (size_ == capacity_) {
JXL_RETURN_IF_ERROR(reserve(capacity_ + 1));
}
data_.address<uint8_t>()[size_++] = x;
return true;
}
size_t size() const { return size_; }
size_t capacity() const { return capacity_; }
uint8_t* data() { return data_.address<uint8_t>(); }
const uint8_t* data() const { return data_.address<uint8_t>(); }
// std::vector operations implemented in terms of the public interface above.
void clear() {
// Not passing on the Status, because resizing to 0 cannot fail.
static_cast<void>(resize(0));
}
bool empty() const { return size() == 0; }
Status assign(std::initializer_list<uint8_t> il) {
JXL_RETURN_IF_ERROR(resize(il.size()));
memcpy(data(), il.begin(), il.size());
return true;
}
uint8_t* begin() { return data(); }
const uint8_t* begin() const { return data(); }
uint8_t* end() { return begin() + size(); }
const uint8_t* end() const { return begin() + size(); }
uint8_t& operator[](const size_t i) {
BoundsCheck(i);
return data()[i];
}
const uint8_t& operator[](const size_t i) const {
BoundsCheck(i);
return data()[i];
}
template <typename T>
Status append(const T& other) {
return append(
reinterpret_cast<const uint8_t*>(other.data()),
reinterpret_cast<const uint8_t*>(other.data()) + other.size());
}
Status append(const uint8_t* begin, const uint8_t* end) {
if (end - begin > 0) {
size_t old_size = size();
JXL_RETURN_IF_ERROR(resize(size() + (end - begin)));
memcpy(data() + old_size, begin, end - begin);
}
return true;
}
private:
Status Init(size_t size) {
size_ = size;
return reserve(size);
}
void BoundsCheck(size_t i) const {
// <= is safe due to padding and required by BitWriter.
JXL_DASSERT(i <= size());
}
JxlMemoryManager* memory_manager_;
size_t size_;
size_t capacity_;
AlignedMemory data_;
};
} // namespace jxl
#endif // LIB_JXL_BASE_PADDED_BYTES_H_