utils/serialize.h

/*
 * Copyright 2011, 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.
 */

#if !defined(SERIALIZE_H)
#define SERIALIZE_H

#include "traits.h"

#include <algorithm>
#include <vector>

#include "utils/rsl_assert.h"
#include <string.h>
#include <stdint.h>
#include <stddef.h>

namespace detail {
  inline bool is_host_little_endian() {
    unsigned long one = 0x1UL;
    return *reinterpret_cast<unsigned char *>(&one);
  }

  inline void swap_byte_order(unsigned char (&array)[1]) {
    // Nothing to do
  }

  inline void swap_byte_order(unsigned char (&array)[2]) {
    std::swap(array[0], array[1]);
  }

  inline void swap_byte_order(unsigned char (&array)[4]) {
    std::swap(array[0], array[3]);
    std::swap(array[1], array[2]);
  }

  inline void swap_byte_order(unsigned char (&array)[8]) {
    std::swap(array[0], array[7]);
    std::swap(array[1], array[6]);
    std::swap(array[2], array[5]);
    std::swap(array[3], array[4]);
  }
}


template <bool isArchiveLittleEndian>
class ArchiveReader {
private:
  unsigned char const *buf_begin;
  unsigned char const *buf_end;
  unsigned char const *cursor;
  unsigned char const *cursor_base;

  bool good;

public:
  ArchiveReader(unsigned char const *buf = NULL, size_t size = 0)
  : buf_begin(buf), buf_end(buf + size),
    cursor(buf), cursor_base(NULL), good(buf != NULL) {
  }

  void prologue(size_t size) {
    rsl_assert(cursor_base == NULL);
    cursor_base = cursor;
  }

  void epilogue(size_t size) {
    rsl_assert(cursor_base != NULL);
    rsl_assert(cursor_base + size >= cursor);
    cursor = cursor_base + size;
    cursor_base = NULL;
  }

  void seek(off_t off, bool from_begin = false) {
    if (from_begin) {
      cursor = buf_begin + off;
    } else {
      cursor += off;
    }
  }

  void readBytes(void *array, size_t size) {
    if (!good || cursor + size > buf_end) {
      good = false;
    } else {
      memcpy(array, cursor, size);
    }
  }

  template <size_t size>
  void operator&(char (&array)[size]) {
    readBytes(array, size);
    seek(size);
  }

  template <size_t size>
  void operator&(unsigned char (&array)[size]) {
    readBytes(array, size);
    seek(size);
  }

  template <typename T>
  void operator&(T &v) {
    seekAlignment<T>();
    readBytes(&v, TypeTraits<T>::size);
    seek(TypeTraits<T>::size);

    if (isArchiveLittleEndian != detail::is_host_little_endian()) {
      detail::swap_byte_order(
        reinterpret_cast<unsigned char (&)[TypeTraits<T>::size]>(v));
    }
  }

  operator void const *() const {
    return good ? this : 0;
  }

  bool operator!() const {
    return !good;
  }

private:
  template <typename T>
  void seekAlignment() {
    size_t align = TypeTraits<T>::align;
    size_t delta = static_cast<size_t>(cursor - buf_begin) % align;

    if (delta > 0) {
      seek(align - delta);
    }
  }

};

typedef ArchiveReader<true>  ArchiveReaderLE;
typedef ArchiveReader<false> ArchiveReaderBE;

#endif // SERIALIZE_H