base/copy_on_write_buffer.cc at main · yoofa/base · GitHub

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/*
 * copy_on_write_buffer.cc
 * Copyright (C) 2024 youfa <vsyfar@gmail.com>
 *
 * Distributed under terms of the GPLv2 license.
 */

#include "base/copy_on_write_buffer.h"

#include <cstddef>
#include <string_view>

namespace ave {
namespace base {

CopyOnWriteBuffer::CopyOnWriteBuffer() : offset_(0), size_(0) {
  AVE_DCHECK(IsConsistent());
}

CopyOnWriteBuffer::CopyOnWriteBuffer(const CopyOnWriteBuffer& buf) = default;

CopyOnWriteBuffer::CopyOnWriteBuffer(CopyOnWriteBuffer&& buf) noexcept
    : buffer_(std::move(buf.buffer_)), offset_(buf.offset_), size_(buf.size_) {
  buf.offset_ = 0;
  buf.size_ = 0;
  AVE_DCHECK(IsConsistent());
}

CopyOnWriteBuffer::CopyOnWriteBuffer(std::string_view s)
    : CopyOnWriteBuffer(s.data(), s.length()) {}

CopyOnWriteBuffer::CopyOnWriteBuffer(size_t size)
    : buffer_(size > 0 ? std::make_shared<Buffer>(size) : nullptr),
      offset_(0),
      size_(size) {
  AVE_DCHECK(IsConsistent());
}

CopyOnWriteBuffer::CopyOnWriteBuffer(size_t size, size_t capacity)
    : buffer_(size > 0 || capacity > 0
                  ? std::make_shared<Buffer>(size, capacity)
                  : nullptr),
      offset_(0),
      size_(size) {
  AVE_DCHECK(IsConsistent());
}

CopyOnWriteBuffer::~CopyOnWriteBuffer() = default;

bool CopyOnWriteBuffer::operator==(const CopyOnWriteBuffer& buf) const {
  // Must either be the same view of the same buffer or have the same contents.
  AVE_DCHECK(IsConsistent());
  AVE_DCHECK(buf.IsConsistent());
  return size_ == buf.size_ &&
         (cdata() == buf.cdata() || memcmp(cdata(), buf.cdata(), size_) == 0);
}

void CopyOnWriteBuffer::SetSize(size_t size) {
  AVE_DCHECK(IsConsistent());
  if (!buffer_) {
    if (size > 0) {
      buffer_ = std::make_shared<Buffer>(size);
      offset_ = 0;
      size_ = size;
    }
    AVE_DCHECK(IsConsistent());
    return;
  }

  if (size <= size_) {
    size_ = size;
    return;
  }

  UnshareAndEnsureCapacity(std::max(capacity(), size));
  buffer_->SetSize(size + offset_);
  size_ = size;
  AVE_DCHECK(IsConsistent());
}

void CopyOnWriteBuffer::EnsureCapacity(size_t new_capacity) {
  AVE_DCHECK(IsConsistent());
  if (!buffer_) {
    if (new_capacity > 0) {
      buffer_ = std::make_shared<Buffer>(0, new_capacity);
      offset_ = 0;
      size_ = 0;
    }
    AVE_DCHECK(IsConsistent());
    return;
  }
  if (new_capacity <= capacity()) {
    return;
  }

  UnshareAndEnsureCapacity(new_capacity);
  AVE_DCHECK(IsConsistent());
}

void CopyOnWriteBuffer::Clear() {
  if (!buffer_) {
    return;
  }

  if (buffer_.use_count() == 1) {
    buffer_->Clear();
  } else {
    buffer_ = std::make_shared<Buffer>(0, capacity());
  }
  offset_ = 0;
  size_ = 0;
  AVE_DCHECK(IsConsistent());
}

void CopyOnWriteBuffer::UnshareAndEnsureCapacity(size_t new_capacity) {
  if (buffer_.use_count() == 1 && new_capacity <= capacity()) {
    return;
  }

  buffer_ =
      std::make_shared<Buffer>(buffer_->data() + offset_, size_, new_capacity);
  offset_ = 0;
  AVE_DCHECK(IsConsistent());
}

}  // namespace base
}  // namespace ave