The Tor Browser: mfbt/Endian.h@97036ab72558 (annotated)

mfbt/Endian.h@97036ab72558 (annotated)

mfbt/Endian.h

Tue, 06 Jan 2015 21:39:09 +0100

author: Michael Schloh von Bennewitz <michael@schloh.com>
date: Tue, 06 Jan 2015 21:39:09 +0100
branch: TOR_BUG_9701
changeset 8: 97036ab72558
permissions: -rw-r--r--

Conditionally force memory storage according to privacy.thirdparty.isolate;
This solves Tor bug #9701, complying with disk avoidance documented in
https://www.torproject.org/projects/torbrowser/design/#disk-avoidance.

 /* -*- 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 magic;
  *     uint32_t length;
  *     uint32_t totalRecords;
  *     uint64_t checksum;
  *
  *   public:
  *     ExampleHeader(const void* data) {
  *       const uint8_t* ptr = static_cast<const uint8_t*>(data);
  *       magic = BigEndian::readUint32(ptr); ptr += sizeof(uint32_t);
  *       length = BigEndian::readUint32(ptr); ptr += sizeof(uint32_t);
  *       totalRecords = BigEndian::readUint32(ptr); ptr += sizeof(uint32_t);
  *       checksum = 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) && _MSC_VER >= 1300
 #  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
 #  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 value)
   {
 #if defined(MOZ_HAVE_BUILTIN_BYTESWAP16)
     return MOZ_HAVE_BUILTIN_BYTESWAP16(value);
 #else
     return T(((value & 0x00ff) << 8) | ((value & 0xff00) >> 8));
 #endif
   }
 };
 template<typename T>
 struct Swapper<T, 4>
 {
   static T swap(T value)
   {
 #if defined(__clang__) || defined(__GNUC__)
     return T(__builtin_bswap32(value));
 #elif defined(_MSC_VER)
     return T(_byteswap_ulong(value));
 #else
     return T(((value & 0x000000ffU) << 24) |
              ((value & 0x0000ff00U) << 8) |
              ((value & 0x00ff0000U) >> 8) |
              ((value & 0xff000000U) >> 24));
 #endif
   }
 };
 template<typename T>
 struct Swapper<T, 8>
 {
   static inline T swap(T value)
   {
 #if defined(__clang__) || defined(__GNUC__)
     return T(__builtin_bswap64(value));
 #elif defined(_MSC_VER)
     return T(_byteswap_uint64(value));
 #else
     return T(((value & 0x00000000000000ffULL) << 56) |
              ((value & 0x000000000000ff00ULL) << 40) |
              ((value & 0x0000000000ff0000ULL) << 24) |
              ((value & 0x00000000ff000000ULL) << 8) |
              ((value & 0x000000ff00000000ULL) >> 8) |
              ((value & 0x0000ff0000000000ULL) >> 24) |
              ((value & 0x00ff000000000000ULL) >> 40) |
              ((value & 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 [dest, dest+count) and [src, src+count]
      * do not overlap.  count is given in bytes.
      */
     static void assertNoOverlap(const void* dest, const void* src, size_t count)
     {
       DebugOnly<const uint8_t*> byteDestPtr = static_cast<const uint8_t*>(dest);
       DebugOnly<const uint8_t*> byteSrcPtr = static_cast<const uint8_t*>(src);
       MOZ_ASSERT((byteDestPtr <= byteSrcPtr &&
                   byteDestPtr + count <= byteSrcPtr) ||
                  (byteSrcPtr <= byteDestPtr &&
                   byteSrcPtr + count <= byteDestPtr));
     }
     template<typename T>
     static void assertAligned(T* ptr)
     {
       MOZ_ASSERT((uintptr_t(ptr) % sizeof(T)) == 0, "Unaligned pointer!");
     }
   protected:
     /**
      * Return |value| converted from SourceEndian encoding to DestEndian
      * encoding.
      */
     template<Endianness SourceEndian, Endianness DestEndian, typename T>
     static inline T maybeSwap(T value)
     {
       if (SourceEndian == DestEndian)
         return value;
       return Swapper<T>::swap(value);
     }
     /**
      * Convert |count| elements at |ptr| from SourceEndian encoding to
      * DestEndian encoding.
      */
     template<Endianness SourceEndian, Endianness DestEndian, typename T>
     static inline void maybeSwapInPlace(T* ptr, size_t count)
     {
       assertAligned(ptr);
       if (SourceEndian == DestEndian)
         return;
       for (size_t i = 0; i < count; i++)
         ptr[i] = Swapper<T>::swap(ptr[i]);
     }
     /**
      * Write |count| elements to the unaligned address |dest| in DestEndian
      * format, using elements found at |src| in SourceEndian format.
      */
     template<Endianness SourceEndian, Endianness DestEndian, typename T>
     static void copyAndSwapTo(void* dest, const T* src, size_t count)
     {
       assertNoOverlap(dest, src, count * sizeof(T));
       assertAligned(src);
       if (SourceEndian == DestEndian) {
         memcpy(dest, src, count * sizeof(T));
         return;
       }
       uint8_t* byteDestPtr = static_cast<uint8_t*>(dest);
       for (size_t i = 0; i < count; ++i) {
         union {
           T val;
           uint8_t buffer[sizeof(T)];
         } u;
         u.val = maybeSwap<SourceEndian, DestEndian>(src[i]);
         memcpy(byteDestPtr, u.buffer, sizeof(T));
         byteDestPtr += sizeof(T);
       }
     }
     /**
      * Write |count| elements to |dest| in DestEndian format, using elements
      * found at the unaligned address |src| in SourceEndian format.
      */
     template<Endianness SourceEndian, Endianness DestEndian, typename T>
     static void copyAndSwapFrom(T* dest, const void* src, size_t count)
     {
       assertNoOverlap(dest, src, count * sizeof(T));
       assertAligned(dest);
       if (SourceEndian == DestEndian) {
         memcpy(dest, src, count * sizeof(T));
         return;
       }
       const uint8_t* byteSrcPtr = static_cast<const uint8_t*>(src);
       for (size_t i = 0; i < count; ++i) {
         union {
           T val;
           uint8_t buffer[sizeof(T)];
         } u;
         memcpy(u.buffer, byteSrcPtr, sizeof(T));
         dest[i] = maybeSwap<SourceEndian, DestEndian>(u.val);
         byteSrcPtr += sizeof(T);
       }
     }
 };
 template<Endianness ThisEndian>
 class Endian : private EndianUtils
 {
   protected:
     /** Read a uint16_t in ThisEndian endianness from |p| and return it. */
     static MOZ_WARN_UNUSED_RESULT uint16_t readUint16(const void* p) {
       return read<uint16_t>(p);
     }
     /** Read a uint32_t in ThisEndian endianness from |p| and return it. */
     static MOZ_WARN_UNUSED_RESULT uint32_t readUint32(const void* p) {
       return read<uint32_t>(p);
     }
     /** Read a uint64_t in ThisEndian endianness from |p| and return it. */
     static MOZ_WARN_UNUSED_RESULT uint64_t readUint64(const void* p) {
       return read<uint64_t>(p);
     }
     /** Read an int16_t in ThisEndian endianness from |p| and return it. */
     static MOZ_WARN_UNUSED_RESULT int16_t readInt16(const void* p) {
       return read<int16_t>(p);
     }
     /** Read an int32_t in ThisEndian endianness from |p| and return it. */
     static MOZ_WARN_UNUSED_RESULT int32_t readInt32(const void* p) {
       return read<uint32_t>(p);
     }
     /** Read an int64_t in ThisEndian endianness from |p| and return it. */
     static MOZ_WARN_UNUSED_RESULT int64_t readInt64(const void* p) {
       return read<int64_t>(p);
     }
     /** Write |val| to |p| using ThisEndian endianness. */
     static void writeUint16(void* p, uint16_t val) {
       write(p, val);
     }
     /** Write |val| to |p| using ThisEndian endianness. */
     static void writeUint32(void* p, uint32_t val) {
       write(p, val);
     }
     /** Write |val| to |p| using ThisEndian endianness. */
     static void writeUint64(void* p, uint64_t val) {
       write(p, val);
     }
     /** Write |val| to |p| using ThisEndian endianness. */
     static void writeInt16(void* p, int16_t val) {
       write(p, val);
     }
     /** Write |val| to |p| using ThisEndian endianness. */
     static void writeInt32(void* p, int32_t val) {
       write(p, val);
     }
     /** Write |val| to |p| using ThisEndian endianness. */
     static void writeInt64(void* p, int64_t val) {
       write(p, val);
     }
     /*
      * 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 value) {
       return maybeSwap<ThisEndian, Little>(value);
     }
     /*
      * Copies count values of type T starting at src to dest, converting
      * them to little-endian format if ThisEndian is Big.
      * As with memcpy, dest and src must not overlap.
      */
     template<typename T>
     static void copyAndSwapToLittleEndian(void* dest, const T* src,
                                           size_t count) {
       copyAndSwapTo<ThisEndian, Little>(dest, src, count);
     }
     /*
      * Likewise, but converts values in place.
      */
     template<typename T>
     static void swapToLittleEndianInPlace(T* p, size_t count) {
       maybeSwapInPlace<ThisEndian, Little>(p, count);
     }
     /*
      * Converts a value of type T to big-endian format.
      */
     template<typename T>
     MOZ_WARN_UNUSED_RESULT static T swapToBigEndian(T value) {
       return maybeSwap<ThisEndian, Big>(value);
     }
     /*
      * Copies count values of type T starting at src to dest, converting
      * them to big-endian format if ThisEndian is Little.
      * As with memcpy, dest and src must not overlap.
      */
     template<typename T>
     static void copyAndSwapToBigEndian(void* dest, const T* src, size_t count) {
       copyAndSwapTo<ThisEndian, Big>(dest, src, count);
     }
     /*
      * Likewise, but converts values in place.
      */
     template<typename T>
     static void swapToBigEndianInPlace(T* p, size_t count) {
       maybeSwapInPlace<ThisEndian, Big>(p, count);
     }
     /*
      * Synonyms for the big-endian functions, for better readability
      * in network code.
      */
     template<typename T>
     MOZ_WARN_UNUSED_RESULT static T swapToNetworkOrder(T value) {
       return swapToBigEndian(value);
     }
     template<typename T>
     static void
     copyAndSwapToNetworkOrder(void* dest, const T* src, size_t count) {
       copyAndSwapToBigEndian(dest, src, count);
     }
     template<typename T>
     static void
     swapToNetworkOrderInPlace(T* p, size_t count) {
       swapToBigEndianInPlace(p, count);
     }
     /*
      * Converts a value of type T from little-endian format.
      */
     template<typename T>
     MOZ_WARN_UNUSED_RESULT static T swapFromLittleEndian(T value) {
       return maybeSwap<Little, ThisEndian>(value);
     }
     /*
      * Copies count values of type T starting at src to dest, converting
      * them to little-endian format if ThisEndian is Big.
      * As with memcpy, dest and src must not overlap.
      */
     template<typename T>
     static void copyAndSwapFromLittleEndian(T* dest, const void* src,
                                             size_t count) {
       copyAndSwapFrom<Little, ThisEndian>(dest, src, count);
     }
     /*
      * Likewise, but converts values in place.
      */
     template<typename T>
     static void swapFromLittleEndianInPlace(T* p, size_t count) {
       maybeSwapInPlace<Little, ThisEndian>(p, count);
     }
     /*
      * Converts a value of type T from big-endian format.
      */
     template<typename T>
     MOZ_WARN_UNUSED_RESULT static T swapFromBigEndian(T value) {
       return maybeSwap<Big, ThisEndian>(value);
     }
     /*
      * Copies count values of type T starting at src to dest, converting
      * them to big-endian format if ThisEndian is Little.
      * As with memcpy, dest and src must not overlap.
      */
     template<typename T>
     static void copyAndSwapFromBigEndian(T* dest, const void* src,
                                          size_t count) {
       copyAndSwapFrom<Big, ThisEndian>(dest, src, count);
     }
     /*
      * Likewise, but converts values in place.
      */
     template<typename T>
     static void swapFromBigEndianInPlace(T* p, size_t count) {
       maybeSwapInPlace<Big, ThisEndian>(p, count);
     }
     /*
      * Synonyms for the big-endian functions, for better readability
      * in network code.
      */
     template<typename T>
     MOZ_WARN_UNUSED_RESULT static T swapFromNetworkOrder(T value) {
       return swapFromBigEndian(value);
     }
     template<typename T>
     static void copyAndSwapFromNetworkOrder(T* dest, const void* src,
                                             size_t count) {
       copyAndSwapFromBigEndian(dest, src, count);
     }
     template<typename T>
     static void swapFromNetworkOrderInPlace(T* p, size_t count) {
       swapFromBigEndianInPlace(p, count);
     }
   private:
     /**
      * Read a value of type T, encoded in endianness ThisEndian from |p|.
      * Return that value encoded in native endianness.
      */
     template<typename T>
     static T read(const void* p) {
       union {
         T val;
         uint8_t buffer[sizeof(T)];
       } u;
       memcpy(u.buffer, p, sizeof(T));
       return maybeSwap<ThisEndian, MOZ_NATIVE_ENDIANNESS>(u.val);
     }
     /**
      * Write a value of type T, in native endianness, to |p|, in ThisEndian
      * endianness.
      */
     template<typename T>
     static void write(void* p, T value) {
       T tmp = maybeSwap<MOZ_NATIVE_ENDIANNESS, ThisEndian>(value);
       memcpy(p, &tmp, sizeof(T));
     }
     Endian() MOZ_DELETE;
     Endian(const Endian& other) MOZ_DELETE;
     void operator=(const Endian& other) MOZ_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 MOZ_FINAL : public detail::EndianReadWrite<detail::Little>
 {};
 class BigEndian MOZ_FINAL : public detail::EndianReadWrite<detail::Big>
 {};
 typedef BigEndian NetworkEndian;
 class NativeEndian MOZ_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 */

The Tor Browser / annotate

mfbt/Endian.h@97036ab72558 (annotated)

mfbt/Endian.h