chromium/components/zucchini/patch_utils.h

// Copyright 2017 The Chromium Authors
// Use of this source code is governed by a BSD-style license that can be
// found in the LICENSE file.

#ifdef UNSAFE_BUFFERS_BUILD
// TODO(crbug.com/40285824): Remove this and convert code to safer constructs.
#pragma allow_unsafe_buffers
#endif

#ifndef COMPONENTS_ZUCCHINI_PATCH_UTILS_H_
#define COMPONENTS_ZUCCHINI_PATCH_UTILS_H_

#include <stdint.h>

#include <iterator>
#include <type_traits>

#include "components/zucchini/image_utils.h"
#include "components/zucchini/version_info.h"

namespace zucchini {

// A Zucchini 'ensemble' patch is the concatenation of a patch header with a
// list of patch 'elements', each containing data for patching individual
// elements.

// Supported by MSVC, g++, and clang++. Ensures no gaps in packing.
#pragma pack(push, 1)

// Header for a Zucchini patch, found at the beginning of an ensemble patch.
struct PatchHeader { … };

// Sanity check.
static_assert …;

// Header for a patch element, found at the beginning of every patch element.
struct PatchElementHeader { … };

// Sanity check.
static_assert …;

#pragma pack(pop)

// Descibes a raw FIX operation.
struct RawDeltaUnit { … };

// A Zucchini patch contains data streams encoded using varint format to reduce
// uncompressed size.

// Writes |value| as a varint in |dst| and returns an iterator pointing beyond
// the written region. |dst| is assumed to hold enough space. Typically, this
// will write to a vector using back insertion, e.g.:
//   EncodeVarUInt(value, std::back_inserter(vector));
template <class T, class It>
It EncodeVarUInt(T value, It dst) { … }

// Same as EncodeVarUInt(), but for signed values.
template <class T, class It>
It EncodeVarInt(T value, It dst) { … }

// Tries to read a varint unsigned integer from |[first, last)|. If
// succesful, writes result into |value| and returns the number of bytes
// read from |[first, last)|. Otherwise returns 0.
template <class T, class It>
typename std::iterator_traits<It>::difference_type DecodeVarUInt(It first,
                                                                 It last,
                                                                 T* value) { … }

// Same as DecodeVarUInt(), but for signed values.
template <class T, class It>
typename std::iterator_traits<It>::difference_type DecodeVarInt(It first,
                                                                It last,
                                                                T* value) { … }

}  // namespace zucchini

#endif  // COMPONENTS_ZUCCHINI_PATCH_UTILS_H_