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gecko-dev/mfbt/Endian.h

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/* -*- Mode: C++; tab-width: 8; indent-tabs-mode: nil; c-basic-offset: 2 -*- */
/* vim: set ts=8 sts=2 et sw=2 tw=80: */
/* This Source Code Form is subject to the terms of the Mozilla Public
* License, v. 2.0. If a copy of the MPL was not distributed with this
* file, You can obtain one at http://mozilla.org/MPL/2.0/. */
/* Functions for reading and writing integers in various endiannesses. */
/*
* The classes LittleEndian and BigEndian expose static methods for
* reading and writing 16-, 32-, and 64-bit signed and unsigned integers
* in their respective endianness. The naming scheme is:
*
* {Little,Big}Endian::{read,write}{Uint,Int}<bitsize>
*
* For instance, LittleEndian::readInt32 will read a 32-bit signed
* integer from memory in little endian format. Similarly,
* BigEndian::writeUint16 will write a 16-bit unsigned integer to memory
* in big-endian format.
*
* The class NativeEndian exposes methods for conversion of existing
* data to and from the native endianness. These methods are intended
* for cases where data needs to be transferred, serialized, etc.
* swap{To,From}{Little,Big}Endian byteswap a single value if necessary.
* Bulk conversion functions are also provided which optimize the
* no-conversion-needed case:
*
* - copyAndSwap{To,From}{Little,Big}Endian;
* - swap{To,From}{Little,Big}EndianInPlace.
*
* The *From* variants are intended to be used for reading data and the
* *To* variants for writing data.
*
* Methods on NativeEndian work with integer data of any type.
* Floating-point data is not supported.
*
* For clarity in networking code, "Network" may be used as a synonym
* for "Big" in any of the above methods or class names.
*
* As an example, reading a file format header whose fields are stored
* in big-endian format might look like:
*
* class ExampleHeader
* {
* private:
* uint32_t mMagic;
* uint32_t mLength;
* uint32_t mTotalRecords;
* uint64_t mChecksum;
*
* public:
* ExampleHeader(const void* data)
* {
* const uint8_t* ptr = static_cast<const uint8_t*>(data);
* mMagic = BigEndian::readUint32(ptr); ptr += sizeof(uint32_t);
* mLength = BigEndian::readUint32(ptr); ptr += sizeof(uint32_t);
* mTotalRecords = BigEndian::readUint32(ptr); ptr += sizeof(uint32_t);
* mChecksum = BigEndian::readUint64(ptr);
* }
* ...
* };
*/
#ifndef mozilla_Endian_h
#define mozilla_Endian_h
#include "mozilla/Assertions.h"
#include "mozilla/Attributes.h"
#include "mozilla/Compiler.h"
#include "mozilla/DebugOnly.h"
#include "mozilla/TypeTraits.h"
#include <stdint.h>
#include <string.h>
#if defined(_MSC_VER)
# include <stdlib.h>
# pragma intrinsic(_byteswap_ushort)
# pragma intrinsic(_byteswap_ulong)
# pragma intrinsic(_byteswap_uint64)
#endif
#if defined(_WIN64)
# if defined(_M_X64) || defined(_M_AMD64) || defined(_AMD64_)
# define MOZ_LITTLE_ENDIAN 1
# else
# error "CPU type is unknown"
# endif
#elif defined(_WIN32)
# if defined(_M_IX86)
# define MOZ_LITTLE_ENDIAN 1
# elif defined(_M_ARM)
# define MOZ_LITTLE_ENDIAN 1
# else
# error "CPU type is unknown"
# endif
#elif defined(__APPLE__) || defined(__powerpc__) || defined(__ppc__)
# if __LITTLE_ENDIAN__
# define MOZ_LITTLE_ENDIAN 1
# elif __BIG_ENDIAN__
# define MOZ_BIG_ENDIAN 1
# endif
#elif defined(__GNUC__) && \
defined(__BYTE_ORDER__) && \
defined(__ORDER_LITTLE_ENDIAN__) && \
defined(__ORDER_BIG_ENDIAN__)
/*
* Some versions of GCC provide architecture-independent macros for
* this. Yes, there are more than two values for __BYTE_ORDER__.
*/
# if __BYTE_ORDER__ == __ORDER_LITTLE_ENDIAN__
# define MOZ_LITTLE_ENDIAN 1
# elif __BYTE_ORDER__ == __ORDER_BIG_ENDIAN__
# define MOZ_BIG_ENDIAN 1
# else
# error "Can't handle mixed-endian architectures"
# endif
/*
* We can't include useful headers like <endian.h> or <sys/isa_defs.h>
* here because they're not present on all platforms. Instead we have
* this big conditional that ideally will catch all the interesting
* cases.
*/
#elif defined(__sparc) || defined(__sparc__) || \
defined(_POWER) || defined(__hppa) || \
defined(_MIPSEB) || defined(__ARMEB__) || \
defined(__s390__) || defined(__AARCH64EB__) || \
(defined(__sh__) && defined(__LITTLE_ENDIAN__)) || \
(defined(__ia64) && defined(__BIG_ENDIAN__))
# define MOZ_BIG_ENDIAN 1
#elif defined(__i386) || defined(__i386__) || \
defined(__x86_64) || defined(__x86_64__) || \
defined(_MIPSEL) || defined(__ARMEL__) || \
defined(__alpha__) || defined(__AARCH64EL__) || \
(defined(__sh__) && defined(__BIG_ENDIAN__)) || \
(defined(__ia64) && !defined(__BIG_ENDIAN__))
# define MOZ_LITTLE_ENDIAN 1
#endif
#if MOZ_BIG_ENDIAN
# define MOZ_LITTLE_ENDIAN 0
#elif MOZ_LITTLE_ENDIAN
# define MOZ_BIG_ENDIAN 0
#else
# error "Cannot determine endianness"
#endif
#if defined(__clang__)
# if __has_builtin(__builtin_bswap16)
# define MOZ_HAVE_BUILTIN_BYTESWAP16 __builtin_bswap16
# endif
#elif defined(__GNUC__)
# if MOZ_GCC_VERSION_AT_LEAST(4, 8, 0)
# define MOZ_HAVE_BUILTIN_BYTESWAP16 __builtin_bswap16
# endif
#elif defined(_MSC_VER)
# define MOZ_HAVE_BUILTIN_BYTESWAP16 _byteswap_ushort
#endif
namespace mozilla {
namespace detail {
/*
* We need wrappers here because free functions with default template
* arguments and/or partial specialization of function templates are not
* supported by all the compilers we use.
*/
template<typename T, size_t Size = sizeof(T)>
struct Swapper;
template<typename T>
struct Swapper<T, 2>
{
static T swap(T aValue)
{
#if defined(MOZ_HAVE_BUILTIN_BYTESWAP16)
return MOZ_HAVE_BUILTIN_BYTESWAP16(aValue);
#else
return T(((aValue & 0x00ff) << 8) | ((aValue & 0xff00) >> 8));
#endif
}
};
template<typename T>
struct Swapper<T, 4>
{
static T swap(T aValue)
{
#if defined(__clang__) || defined(__GNUC__)
return T(__builtin_bswap32(aValue));
#elif defined(_MSC_VER)
return T(_byteswap_ulong(aValue));
#else
return T(((aValue & 0x000000ffU) << 24) |
((aValue & 0x0000ff00U) << 8) |
((aValue & 0x00ff0000U) >> 8) |
((aValue & 0xff000000U) >> 24));
#endif
}
};
template<typename T>
struct Swapper<T, 8>
{
static inline T swap(T aValue)
{
#if defined(__clang__) || defined(__GNUC__)
return T(__builtin_bswap64(aValue));
#elif defined(_MSC_VER)
return T(_byteswap_uint64(aValue));
#else
return T(((aValue & 0x00000000000000ffULL) << 56) |
((aValue & 0x000000000000ff00ULL) << 40) |
((aValue & 0x0000000000ff0000ULL) << 24) |
((aValue & 0x00000000ff000000ULL) << 8) |
((aValue & 0x000000ff00000000ULL) >> 8) |
((aValue & 0x0000ff0000000000ULL) >> 24) |
((aValue & 0x00ff000000000000ULL) >> 40) |
((aValue & 0xff00000000000000ULL) >> 56));
#endif
}
};
enum Endianness { Little, Big };
#if MOZ_BIG_ENDIAN
# define MOZ_NATIVE_ENDIANNESS detail::Big
#else
# define MOZ_NATIVE_ENDIANNESS detail::Little
#endif
class EndianUtils
{
/**
* Assert that the memory regions [aDest, aDest+aCount) and
* [aSrc, aSrc+aCount] do not overlap. aCount is given in bytes.
*/
static void assertNoOverlap(const void* aDest, const void* aSrc,
size_t aCount)
{
DebugOnly<const uint8_t*> byteDestPtr = static_cast<const uint8_t*>(aDest);
DebugOnly<const uint8_t*> byteSrcPtr = static_cast<const uint8_t*>(aSrc);
MOZ_ASSERT((byteDestPtr <= byteSrcPtr &&
byteDestPtr + aCount <= byteSrcPtr) ||
(byteSrcPtr <= byteDestPtr &&
byteSrcPtr + aCount <= byteDestPtr));
}
template<typename T>
static void assertAligned(T* aPtr)
{
MOZ_ASSERT((uintptr_t(aPtr) % sizeof(T)) == 0, "Unaligned pointer!");
}
protected:
/**
* Return |aValue| converted from SourceEndian encoding to DestEndian
* encoding.
*/
template<Endianness SourceEndian, Endianness DestEndian, typename T>
static inline T maybeSwap(T aValue)
{
if (SourceEndian == DestEndian) {
return aValue;
}
return Swapper<T>::swap(aValue);
}
/**
* Convert |aCount| elements at |aPtr| from SourceEndian encoding to
* DestEndian encoding.
*/
template<Endianness SourceEndian, Endianness DestEndian, typename T>
static inline void maybeSwapInPlace(T* aPtr, size_t aCount)
{
assertAligned(aPtr);
if (SourceEndian == DestEndian) {
return;
}
for (size_t i = 0; i < aCount; i++) {
aPtr[i] = Swapper<T>::swap(aPtr[i]);
}
}
/**
* Write |aCount| elements to the unaligned address |aDest| in DestEndian
* format, using elements found at |aSrc| in SourceEndian format.
*/
template<Endianness SourceEndian, Endianness DestEndian, typename T>
static void copyAndSwapTo(void* aDest, const T* aSrc, size_t aCount)
{
assertNoOverlap(aDest, aSrc, aCount * sizeof(T));
assertAligned(aSrc);
if (SourceEndian == DestEndian) {
memcpy(aDest, aSrc, aCount * sizeof(T));
return;
}
uint8_t* byteDestPtr = static_cast<uint8_t*>(aDest);
for (size_t i = 0; i < aCount; ++i) {
union
{
T mVal;
uint8_t mBuffer[sizeof(T)];
} u;
u.mVal = maybeSwap<SourceEndian, DestEndian>(aSrc[i]);
memcpy(byteDestPtr, u.mBuffer, sizeof(T));
byteDestPtr += sizeof(T);
}
}
/**
* Write |aCount| elements to |aDest| in DestEndian format, using elements
* found at the unaligned address |aSrc| in SourceEndian format.
*/
template<Endianness SourceEndian, Endianness DestEndian, typename T>
static void copyAndSwapFrom(T* aDest, const void* aSrc, size_t aCount)
{
assertNoOverlap(aDest, aSrc, aCount * sizeof(T));
assertAligned(aDest);
if (SourceEndian == DestEndian) {
memcpy(aDest, aSrc, aCount * sizeof(T));
return;
}
const uint8_t* byteSrcPtr = static_cast<const uint8_t*>(aSrc);
for (size_t i = 0; i < aCount; ++i) {
union
{
T mVal;
uint8_t mBuffer[sizeof(T)];
} u;
memcpy(u.mBuffer, byteSrcPtr, sizeof(T));
aDest[i] = maybeSwap<SourceEndian, DestEndian>(u.mVal);
byteSrcPtr += sizeof(T);
}
}
};
template<Endianness ThisEndian>
class Endian : private EndianUtils
{
protected:
/** Read a uint16_t in ThisEndian endianness from |aPtr| and return it. */
static MOZ_WARN_UNUSED_RESULT uint16_t readUint16(const void* aPtr)
{
return read<uint16_t>(aPtr);
}
/** Read a uint32_t in ThisEndian endianness from |aPtr| and return it. */
static MOZ_WARN_UNUSED_RESULT uint32_t readUint32(const void* aPtr)
{
return read<uint32_t>(aPtr);
}
/** Read a uint64_t in ThisEndian endianness from |aPtr| and return it. */
static MOZ_WARN_UNUSED_RESULT uint64_t readUint64(const void* aPtr)
{
return read<uint64_t>(aPtr);
}
/** Read an int16_t in ThisEndian endianness from |aPtr| and return it. */
static MOZ_WARN_UNUSED_RESULT int16_t readInt16(const void* aPtr)
{
return read<int16_t>(aPtr);
}
/** Read an int32_t in ThisEndian endianness from |aPtr| and return it. */
static MOZ_WARN_UNUSED_RESULT int32_t readInt32(const void* aPtr)
{
return read<uint32_t>(aPtr);
}
/** Read an int64_t in ThisEndian endianness from |aPtr| and return it. */
static MOZ_WARN_UNUSED_RESULT int64_t readInt64(const void* aPtr)
{
return read<int64_t>(aPtr);
}
/** Write |aValue| to |aPtr| using ThisEndian endianness. */
static void writeUint16(void* aPtr, uint16_t aValue)
{
write(aPtr, aValue);
}
/** Write |aValue| to |aPtr| using ThisEndian endianness. */
static void writeUint32(void* aPtr, uint32_t aValue)
{
write(aPtr, aValue);
}
/** Write |aValue| to |aPtr| using ThisEndian endianness. */
static void writeUint64(void* aPtr, uint64_t aValue)
{
write(aPtr, aValue);
}
/** Write |aValue| to |aPtr| using ThisEndian endianness. */
static void writeInt16(void* aPtr, int16_t aValue)
{
write(aPtr, aValue);
}
/** Write |aValue| to |aPtr| using ThisEndian endianness. */
static void writeInt32(void* aPtr, int32_t aValue)
{
write(aPtr, aValue);
}
/** Write |aValue| to |aPtr| using ThisEndian endianness. */
static void writeInt64(void* aPtr, int64_t aValue)
{
write(aPtr, aValue);
}
/*
* Converts a value of type T to little-endian format.
*
* This function is intended for cases where you have data in your
* native-endian format and you need it to appear in little-endian
* format for transmission.
*/
template<typename T>
MOZ_WARN_UNUSED_RESULT static T swapToLittleEndian(T aValue)
{
return maybeSwap<ThisEndian, Little>(aValue);
}
/*
* Copies |aCount| values of type T starting at |aSrc| to |aDest|, converting
* them to little-endian format if ThisEndian is Big.
* As with memcpy, |aDest| and |aSrc| must not overlap.
*/
template<typename T>
static void copyAndSwapToLittleEndian(void* aDest, const T* aSrc,
size_t aCount)
{
copyAndSwapTo<ThisEndian, Little>(aDest, aSrc, aCount);
}
/*
* Likewise, but converts values in place.
*/
template<typename T>
static void swapToLittleEndianInPlace(T* aPtr, size_t aCount)
{
maybeSwapInPlace<ThisEndian, Little>(aPtr, aCount);
}
/*
* Converts a value of type T to big-endian format.
*/
template<typename T>
MOZ_WARN_UNUSED_RESULT static T swapToBigEndian(T aValue)
{
return maybeSwap<ThisEndian, Big>(aValue);
}
/*
* Copies |aCount| values of type T starting at |aSrc| to |aDest|, converting
* them to big-endian format if ThisEndian is Little.
* As with memcpy, |aDest| and |aSrc| must not overlap.
*/
template<typename T>
static void copyAndSwapToBigEndian(void* aDest, const T* aSrc,
size_t aCount)
{
copyAndSwapTo<ThisEndian, Big>(aDest, aSrc, aCount);
}
/*
* Likewise, but converts values in place.
*/
template<typename T>
static void swapToBigEndianInPlace(T* aPtr, size_t aCount)
{
maybeSwapInPlace<ThisEndian, Big>(aPtr, aCount);
}
/*
* Synonyms for the big-endian functions, for better readability
* in network code.
*/
template<typename T>
MOZ_WARN_UNUSED_RESULT static T swapToNetworkOrder(T aValue)
{
return swapToBigEndian(aValue);
}
template<typename T>
static void
copyAndSwapToNetworkOrder(void* aDest, const T* aSrc, size_t aCount)
{
copyAndSwapToBigEndian(aDest, aSrc, aCount);
}
template<typename T>
static void
swapToNetworkOrderInPlace(T* aPtr, size_t aCount)
{
swapToBigEndianInPlace(aPtr, aCount);
}
/*
* Converts a value of type T from little-endian format.
*/
template<typename T>
MOZ_WARN_UNUSED_RESULT static T swapFromLittleEndian(T aValue)
{
return maybeSwap<Little, ThisEndian>(aValue);
}
/*
* Copies |aCount| values of type T starting at |aSrc| to |aDest|, converting
* them to little-endian format if ThisEndian is Big.
* As with memcpy, |aDest| and |aSrc| must not overlap.
*/
template<typename T>
static void copyAndSwapFromLittleEndian(T* aDest, const void* aSrc,
size_t aCount)
{
copyAndSwapFrom<Little, ThisEndian>(aDest, aSrc, aCount);
}
/*
* Likewise, but converts values in place.
*/
template<typename T>
static void swapFromLittleEndianInPlace(T* aPtr, size_t aCount)
{
maybeSwapInPlace<Little, ThisEndian>(aPtr, aCount);
}
/*
* Converts a value of type T from big-endian format.
*/
template<typename T>
MOZ_WARN_UNUSED_RESULT static T swapFromBigEndian(T aValue)
{
return maybeSwap<Big, ThisEndian>(aValue);
}
/*
* Copies |aCount| values of type T starting at |aSrc| to |aDest|, converting
* them to big-endian format if ThisEndian is Little.
* As with memcpy, |aDest| and |aSrc| must not overlap.
*/
template<typename T>
static void copyAndSwapFromBigEndian(T* aDest, const void* aSrc,
size_t aCount)
{
copyAndSwapFrom<Big, ThisEndian>(aDest, aSrc, aCount);
}
/*
* Likewise, but converts values in place.
*/
template<typename T>
static void swapFromBigEndianInPlace(T* aPtr, size_t aCount)
{
maybeSwapInPlace<Big, ThisEndian>(aPtr, aCount);
}
/*
* Synonyms for the big-endian functions, for better readability
* in network code.
*/
template<typename T>
MOZ_WARN_UNUSED_RESULT static T swapFromNetworkOrder(T aValue)
{
return swapFromBigEndian(aValue);
}
template<typename T>
static void copyAndSwapFromNetworkOrder(T* aDest, const void* aSrc,
size_t aCount)
{
copyAndSwapFromBigEndian(aDest, aSrc, aCount);
}
template<typename T>
static void swapFromNetworkOrderInPlace(T* aPtr, size_t aCount)
{
swapFromBigEndianInPlace(aPtr, aCount);
}
private:
/**
* Read a value of type T, encoded in endianness ThisEndian from |aPtr|.
* Return that value encoded in native endianness.
*/
template<typename T>
static T read(const void* aPtr)
{
union
{
T mVal;
uint8_t mBuffer[sizeof(T)];
} u;
memcpy(u.mBuffer, aPtr, sizeof(T));
return maybeSwap<ThisEndian, MOZ_NATIVE_ENDIANNESS>(u.mVal);
}
/**
* Write a value of type T, in native endianness, to |aPtr|, in ThisEndian
* endianness.
*/
template<typename T>
static void write(void* aPtr, T aValue)
{
T tmp = maybeSwap<MOZ_NATIVE_ENDIANNESS, ThisEndian>(aValue);
memcpy(aPtr, &tmp, sizeof(T));
}
Endian() = delete;
Endian(const Endian& aTther) = delete;
void operator=(const Endian& aOther) = delete;
};
template<Endianness ThisEndian>
class EndianReadWrite : public Endian<ThisEndian>
{
private:
typedef Endian<ThisEndian> super;
public:
using super::readUint16;
using super::readUint32;
using super::readUint64;
using super::readInt16;
using super::readInt32;
using super::readInt64;
using super::writeUint16;
using super::writeUint32;
using super::writeUint64;
using super::writeInt16;
using super::writeInt32;
using super::writeInt64;
};
} /* namespace detail */
class LittleEndian final : public detail::EndianReadWrite<detail::Little>
{};
class BigEndian final : public detail::EndianReadWrite<detail::Big>
{};
typedef BigEndian NetworkEndian;
class NativeEndian final : public detail::Endian<MOZ_NATIVE_ENDIANNESS>
{
private:
typedef detail::Endian<MOZ_NATIVE_ENDIANNESS> super;
public:
/*
* These functions are intended for cases where you have data in your
* native-endian format and you need the data to appear in the appropriate
* endianness for transmission, serialization, etc.
*/
using super::swapToLittleEndian;
using super::copyAndSwapToLittleEndian;
using super::swapToLittleEndianInPlace;
using super::swapToBigEndian;
using super::copyAndSwapToBigEndian;
using super::swapToBigEndianInPlace;
using super::swapToNetworkOrder;
using super::copyAndSwapToNetworkOrder;
using super::swapToNetworkOrderInPlace;
/*
* These functions are intended for cases where you have data in the
* given endianness (e.g. reading from disk or a file-format) and you
* need the data to appear in native-endian format for processing.
*/
using super::swapFromLittleEndian;
using super::copyAndSwapFromLittleEndian;
using super::swapFromLittleEndianInPlace;
using super::swapFromBigEndian;
using super::copyAndSwapFromBigEndian;
using super::swapFromBigEndianInPlace;
using super::swapFromNetworkOrder;
using super::copyAndSwapFromNetworkOrder;
using super::swapFromNetworkOrderInPlace;
};
#undef MOZ_NATIVE_ENDIANNESS
} /* namespace mozilla */
#endif /* mozilla_Endian_h */
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