src/net/base/big_endian.h

// Copyright (c) 2011 The Chromium 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 NET_BASE_BIG_ENDIAN_H_
#define NET_BASE_BIG_ENDIAN_H_

#include "base/basictypes.h"
#include "base/string_piece.h"
#include "net/base/net_export.h"

namespace net {

// Read an integer (signed or unsigned) from |buf| in Big Endian order.
// Note: this loop is unrolled with -O1 and above.
// NOTE(szym): glibc dns-canon.c and SpdyFrameBuilder use
// ntohs(*(uint16_t*)ptr) which is potentially unaligned.
// This would cause SIGBUS on ARMv5 or earlier and ARMv6-M.
template<typename T>
inline void ReadBigEndian(const char buf[], T* out) {
  *out = buf[0];
  for (size_t i = 1; i < sizeof(T); ++i) {
    *out <<= 8;
    // Must cast to uint8 to avoid clobbering by sign extension.
    *out |= static_cast<uint8>(buf[i]);
  }
}

// Write an integer (signed or unsigned) |val| to |buf| in Big Endian order.
// Note: this loop is unrolled with -O1 and above.
template<typename T>
inline void WriteBigEndian(char buf[], T val) {
  for (size_t i = 0; i < sizeof(T); ++i) {
    buf[sizeof(T)-i-1] = static_cast<char>(val & 0xFF);
    val >>= 8;
  }
}

// Specializations to make clang happy about the (dead code) shifts above.
template<>
inline void ReadBigEndian<uint8>(const char buf[], uint8* out) {
  *out = buf[0];
}

template<>
inline void WriteBigEndian<uint8>(char buf[], uint8 val) {
  buf[0] = static_cast<char>(val);
}

// Allows reading integers in network order (big endian) while iterating over
// an underlying buffer. All the reading functions advance the internal pointer.
class NET_EXPORT BigEndianReader {
 public:
  BigEndianReader(const void* buf, size_t len);

  const char* ptr() const { return ptr_; }
  std::ptrdiff_t remaining() const { return end_ - ptr_; }

  bool Skip(size_t len);
  bool ReadBytes(void* out, size_t len);
  // Creates a StringPiece in |out| that points to the underlying buffer.
  bool ReadPiece(base::StringPiece* out, size_t len);
  bool ReadU8(uint8* value);
  bool ReadU16(uint16* value);
  bool ReadU32(uint32* value);

 private:
  // Hidden to promote type safety.
  template<typename T>
  bool Read(T* v);

  const char* ptr_;
  const char* end_;
};

// Allows writing integers in network order (big endian) while iterating over
// an underlying buffer. All the writing functions advance the internal pointer.
class NET_EXPORT BigEndianWriter {
 public:
  BigEndianWriter(void* buf, size_t len);

  char* ptr() const { return ptr_; }
  std::ptrdiff_t remaining() const { return end_ - ptr_; }

  bool Skip(size_t len);
  bool WriteBytes(const void* buf, size_t len);
  bool WriteU8(uint8 value);
  bool WriteU16(uint16 value);
  bool WriteU32(uint32 value);

 private:
  // Hidden to promote type safety.
  template<typename T>
  bool Write(T v);

  char* ptr_;
  char* end_;
};

}  // namespace net

#endif  // NET_BASE_BIG_ENDIAN_H_