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// Copyright 2019 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 UTIL_BIG_ENDIAN_H_
#define UTIL_BIG_ENDIAN_H_
#include <stdint.h>
#include <cstring>
#include <type_traits>
namespace openscreen {
////////////////////////////////////////////////////////////////////////////////
// Note: All of the functions here are defined inline, as any half-decent
// compiler will optimize them to a single integer constant or single
// instruction on most architectures.
////////////////////////////////////////////////////////////////////////////////
// Returns true if this code is running on a big-endian architecture.
inline bool IsBigEndianArchitecture() {
const uint16_t kTestWord = 0x0100;
uint8_t bytes[sizeof(kTestWord)];
memcpy(bytes, &kTestWord, sizeof(bytes));
return !!bytes[0];
}
// Returns the bytes of |x| in reverse order. This is only defined for 16-, 32-,
// and 64-bit unsigned integers.
template <typename Integer>
Integer ByteSwap(Integer x);
template <>
inline uint8_t ByteSwap(uint8_t x) {
return x;
}
#if defined(__clang__) || defined(__GNUC__)
template <>
inline uint64_t ByteSwap(uint64_t x) {
return __builtin_bswap64(x);
}
template <>
inline uint32_t ByteSwap(uint32_t x) {
return __builtin_bswap32(x);
}
template <>
inline uint16_t ByteSwap(uint16_t x) {
return __builtin_bswap16(x);
}
#elif defined(_MSC_VER)
template <>
inline uint64_t ByteSwap(uint64_t x) {
return _byteswap_uint64(x);
}
template <>
inline uint32_t ByteSwap(uint32_t x) {
return _byteswap_ulong(x);
}
template <>
inline uint16_t ByteSwap(uint16_t x) {
return _byteswap_ushort(x);
}
#else
#include <byteswap.h>
template <>
inline uint64_t ByteSwap(uint64_t x) {
return bswap_64(x);
}
template <>
inline uint32_t ByteSwap(uint32_t x) {
return bswap_32(x);
}
template <>
inline uint16_t ByteSwap(uint16_t x) {
return bswap_16(x);
}
#endif
// Read a POD integer from |src| in big-endian byte order, returning the integer
// in native byte order.
template <typename Integer>
inline Integer ReadBigEndian(const void* src) {
Integer result;
memcpy(&result, src, sizeof(result));
if (!IsBigEndianArchitecture()) {
result = ByteSwap<typename std::make_unsigned<Integer>::type>(result);
}
return result;
}
// Write a POD integer |val| to |dest| in big-endian byte order.
template <typename Integer>
inline void WriteBigEndian(Integer val, void* dest) {
if (!IsBigEndianArchitecture()) {
val = ByteSwap<typename std::make_unsigned<Integer>::type>(val);
}
memcpy(dest, &val, sizeof(val));
}
template <class T>
class BigEndianBuffer {
public:
class Cursor {
public:
Cursor(BigEndianBuffer* buffer)
: buffer_(buffer), origin_(buffer_->current_) {}
Cursor(const Cursor& other) = delete;
Cursor(Cursor&& other) = delete;
~Cursor() { buffer_->current_ = origin_; }
Cursor& operator=(const Cursor& other) = delete;
Cursor& operator=(Cursor&& other) = delete;
void Commit() { origin_ = buffer_->current_; }
T* origin() { return origin_; }
size_t delta() { return buffer_->current_ - origin_; }
private:
BigEndianBuffer* buffer_;
T* origin_;
};
bool Skip(size_t length) {
if (current_ + length > end_) {
return false;
}
current_ += length;
return true;
}
T* begin() const { return begin_; }
T* current() const { return current_; }
T* end() const { return end_; }
size_t length() const { return end_ - begin_; }
size_t remaining() const { return end_ - current_; }
size_t offset() const { return current_ - begin_; }
BigEndianBuffer(T* buffer, size_t length)
: begin_(buffer), current_(buffer), end_(buffer + length) {}
BigEndianBuffer(const BigEndianBuffer&) = delete;
BigEndianBuffer& operator=(const BigEndianBuffer&) = delete;
private:
T* begin_;
T* current_;
T* end_;
};
class BigEndianReader : public BigEndianBuffer<const uint8_t> {
public:
BigEndianReader(const uint8_t* buffer, size_t length);
template <typename T>
bool Read(T* out) {
const uint8_t* read_position = current();
if (Skip(sizeof(T))) {
*out = ReadBigEndian<T>(read_position);
return true;
}
return false;
}
bool Read(size_t length, void* out);
};
class BigEndianWriter : public BigEndianBuffer<uint8_t> {
public:
BigEndianWriter(uint8_t* buffer, size_t length);
template <typename T>
bool Write(T value) {
uint8_t* write_position = current();
if (Skip(sizeof(T))) {
WriteBigEndian<T>(value, write_position);
return true;
}
return false;
}
bool Write(const void* buffer, size_t length);
};
} // namespace openscreen
#endif // UTIL_BIG_ENDIAN_H_
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