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

mfbt/MathAlgorithms.h@97036ab72558 (annotated)

mfbt/MathAlgorithms.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/. */
 /* mfbt maths algorithms. */
 #ifndef mozilla_MathAlgorithms_h
 #define mozilla_MathAlgorithms_h
 #include "mozilla/Assertions.h"
 #include "mozilla/TypeTraits.h"
 #include <cmath>
 #include <limits.h>
 #include <stdint.h>
 namespace mozilla {
 // Greatest Common Divisor
 template<typename IntegerType>
 MOZ_ALWAYS_INLINE IntegerType
 EuclidGCD(IntegerType a, IntegerType b)
 {
   // Euclid's algorithm; O(N) in the worst case.  (There are better
   // ways, but we don't need them for the current use of this algo.)
   MOZ_ASSERT(a > 0);
   MOZ_ASSERT(b > 0);
   while (a != b) {
     if (a > b) {
       a = a - b;
     } else {
       b = b - a;
     }
   }
   return a;
 }
 // Least Common Multiple
 template<typename IntegerType>
 MOZ_ALWAYS_INLINE IntegerType
 EuclidLCM(IntegerType a, IntegerType b)
 {
   // Divide first to reduce overflow risk.
   return (a / EuclidGCD(a, b)) * b;
 }
 namespace detail {
 template<typename T>
 struct AllowDeprecatedAbsFixed : FalseType {};
 template<> struct AllowDeprecatedAbsFixed<int32_t> : TrueType {};
 template<> struct AllowDeprecatedAbsFixed<int64_t> : TrueType {};
 template<typename T>
 struct AllowDeprecatedAbs : AllowDeprecatedAbsFixed<T> {};
 template<> struct AllowDeprecatedAbs<int> : TrueType {};
 template<> struct AllowDeprecatedAbs<long> : TrueType {};
 } // namespace detail
 // DO NOT USE DeprecatedAbs.  It exists only until its callers can be converted
 // to Abs below, and it will be removed when all callers have been changed.
 template<typename T>
 inline typename mozilla::EnableIf<detail::AllowDeprecatedAbs<T>::value, T>::Type
 DeprecatedAbs(const T t)
 {
   // The absolute value of the smallest possible value of a signed-integer type
   // won't fit in that type (on twos-complement systems -- and we're blithely
   // assuming we're on such systems, for the non-<stdint.h> types listed above),
   // so assert that the input isn't that value.
   //
   // This is the case if: the value is non-negative; or if adding one (giving a
   // value in the range [-maxvalue, 0]), then negating (giving a value in the
   // range [0, maxvalue]), doesn't produce maxvalue (because in twos-complement,
   // (minvalue + 1) == -maxvalue).
   MOZ_ASSERT(t >= 0 ||
              -(t + 1) != T((1ULL << (CHAR_BIT * sizeof(T) - 1)) - 1),
              "You can't negate the smallest possible negative integer!");
   return t >= 0 ? t : -t;
 }
 namespace detail {
 // For now mozilla::Abs only takes intN_T, the signed natural types, and
 // float/double/long double.  Feel free to add overloads for other standard,
 // signed types if you need them.
 template<typename T>
 struct AbsReturnTypeFixed;
 template<> struct AbsReturnTypeFixed<int8_t> { typedef uint8_t Type; };
 template<> struct AbsReturnTypeFixed<int16_t> { typedef uint16_t Type; };
 template<> struct AbsReturnTypeFixed<int32_t> { typedef uint32_t Type; };
 template<> struct AbsReturnTypeFixed<int64_t> { typedef uint64_t Type; };
 template<typename T>
 struct AbsReturnType : AbsReturnTypeFixed<T> {};
 template<> struct AbsReturnType<char> : EnableIf<char(-1) < char(0), unsigned char> {};
 template<> struct AbsReturnType<signed char> { typedef unsigned char Type; };
 template<> struct AbsReturnType<short> { typedef unsigned short Type; };
 template<> struct AbsReturnType<int> { typedef unsigned int Type; };
 template<> struct AbsReturnType<long> { typedef unsigned long Type; };
 template<> struct AbsReturnType<long long> { typedef unsigned long long Type; };
 template<> struct AbsReturnType<float> { typedef float Type; };
 template<> struct AbsReturnType<double> { typedef double Type; };
 template<> struct AbsReturnType<long double> { typedef long double Type; };
 } // namespace detail
 template<typename T>
 inline typename detail::AbsReturnType<T>::Type
 Abs(const T t)
 {
   typedef typename detail::AbsReturnType<T>::Type ReturnType;
   return t >= 0 ? ReturnType(t) : ~ReturnType(t) + 1;
 }
 template<>
 inline float
 Abs<float>(const float f)
 {
   return std::fabs(f);
 }
 template<>
 inline double
 Abs<double>(const double d)
 {
   return std::fabs(d);
 }
 template<>
 inline long double
 Abs<long double>(const long double d)
 {
   return std::fabs(d);
 }
 } // namespace mozilla
 #if defined(_WIN32) && (_MSC_VER >= 1300) && (defined(_M_IX86) || defined(_M_AMD64) || defined(_M_X64))
 #  define MOZ_BITSCAN_WINDOWS
   extern "C" {
     unsigned char _BitScanForward(unsigned long* Index, unsigned long mask);
     unsigned char _BitScanReverse(unsigned long* Index, unsigned long mask);
 #  pragma intrinsic(_BitScanForward, _BitScanReverse)
 #  if defined(_M_AMD64) || defined(_M_X64)
 #    define MOZ_BITSCAN_WINDOWS64
     unsigned char _BitScanForward64(unsigned long* index, unsigned __int64 mask);
     unsigned char _BitScanReverse64(unsigned long* index, unsigned __int64 mask);
 #   pragma intrinsic(_BitScanForward64, _BitScanReverse64)
 #  endif
   } // extern "C"
 #endif
 namespace mozilla {
 namespace detail {
 #if defined(MOZ_BITSCAN_WINDOWS)
   inline uint_fast8_t
   CountLeadingZeroes32(uint32_t u)
   {
     unsigned long index;
     _BitScanReverse(&index, static_cast<unsigned long>(u));
     return uint_fast8_t(31 - index);
   }
   inline uint_fast8_t
   CountTrailingZeroes32(uint32_t u)
   {
     unsigned long index;
     _BitScanForward(&index, static_cast<unsigned long>(u));
     return uint_fast8_t(index);
   }
   inline uint_fast8_t
   CountPopulation32(uint32_t u)
   {
     uint32_t x = u - ((u >> 1) & 0x55555555);
     x = (x & 0x33333333) + ((x >> 2) & 0x33333333);
     return (((x + (x >> 4)) & 0xf0f0f0f) * 0x1010101) >> 24;
   }
   inline uint_fast8_t
   CountLeadingZeroes64(uint64_t u)
   {
 #  if defined(MOZ_BITSCAN_WINDOWS64)
     unsigned long index;
     _BitScanReverse64(&index, static_cast<unsigned __int64>(u));
     return uint_fast8_t(63 - index);
 #  else
     uint32_t hi = uint32_t(u >> 32);
     if (hi != 0)
       return CountLeadingZeroes32(hi);
     return 32 + CountLeadingZeroes32(uint32_t(u));
 #  endif
   }
   inline uint_fast8_t
   CountTrailingZeroes64(uint64_t u)
   {
 #  if defined(MOZ_BITSCAN_WINDOWS64)
     unsigned long index;
     _BitScanForward64(&index, static_cast<unsigned __int64>(u));
     return uint_fast8_t(index);
 #  else
     uint32_t lo = uint32_t(u);
     if (lo != 0)
       return CountTrailingZeroes32(lo);
     return 32 + CountTrailingZeroes32(uint32_t(u >> 32));
 #  endif
   }
 #  ifdef MOZ_HAVE_BITSCAN64
 #    undef MOZ_HAVE_BITSCAN64
 #  endif
 #elif defined(__clang__) || defined(__GNUC__)
 #  if defined(__clang__)
 #    if !__has_builtin(__builtin_ctz) || !__has_builtin(__builtin_clz)
 #      error "A clang providing __builtin_c[lt]z is required to build"
 #    endif
 #  else
      // gcc has had __builtin_clz and friends since 3.4: no need to check.
 #  endif
   inline uint_fast8_t
   CountLeadingZeroes32(uint32_t u)
   {
     return __builtin_clz(u);
   }
   inline uint_fast8_t
   CountTrailingZeroes32(uint32_t u)
   {
     return __builtin_ctz(u);
   }
   inline uint_fast8_t
   CountPopulation32(uint32_t u)
   {
     return __builtin_popcount(u);
   }
   inline uint_fast8_t
   CountLeadingZeroes64(uint64_t u)
   {
     return __builtin_clzll(u);
   }
   inline uint_fast8_t
   CountTrailingZeroes64(uint64_t u)
   {
     return __builtin_ctzll(u);
   }
 #else
 #  error "Implement these!"
   inline uint_fast8_t CountLeadingZeroes32(uint32_t u) MOZ_DELETE;
   inline uint_fast8_t CountTrailingZeroes32(uint32_t u) MOZ_DELETE;
   inline uint_fast8_t CountPopulation32(uint32_t u) MOZ_DELETE;
   inline uint_fast8_t CountLeadingZeroes64(uint64_t u) MOZ_DELETE;
   inline uint_fast8_t CountTrailingZeroes64(uint64_t u) MOZ_DELETE;
 #endif
 } // namespace detail
 /**
  * Compute the number of high-order zero bits in the NON-ZERO number |u|.  That
  * is, looking at the bitwise representation of the number, with the highest-
  * valued bits at the start, return the number of zeroes before the first one
  * is observed.
  *
  * CountLeadingZeroes32(0xF0FF1000) is 0;
  * CountLeadingZeroes32(0x7F8F0001) is 1;
  * CountLeadingZeroes32(0x3FFF0100) is 2;
  * CountLeadingZeroes32(0x1FF50010) is 3; and so on.
  */
 inline uint_fast8_t
 CountLeadingZeroes32(uint32_t u)
 {
   MOZ_ASSERT(u != 0);
   return detail::CountLeadingZeroes32(u);
 }
 /**
  * Compute the number of low-order zero bits in the NON-ZERO number |u|.  That
  * is, looking at the bitwise representation of the number, with the lowest-
  * valued bits at the start, return the number of zeroes before the first one
  * is observed.
  *
  * CountTrailingZeroes32(0x0100FFFF) is 0;
  * CountTrailingZeroes32(0x7000FFFE) is 1;
  * CountTrailingZeroes32(0x0080FFFC) is 2;
  * CountTrailingZeroes32(0x0080FFF8) is 3; and so on.
  */
 inline uint_fast8_t
 CountTrailingZeroes32(uint32_t u)
 {
   MOZ_ASSERT(u != 0);
   return detail::CountTrailingZeroes32(u);
 }
 /**
  * Compute the number of one bits in the number |u|,
  */
 inline uint_fast8_t
 CountPopulation32(uint32_t u)
 {
   return detail::CountPopulation32(u);
 }
 /** Analogous to CountLeadingZeroes32, but for 64-bit numbers. */
 inline uint_fast8_t
 CountLeadingZeroes64(uint64_t u)
 {
   MOZ_ASSERT(u != 0);
   return detail::CountLeadingZeroes64(u);
 }
 /** Analogous to CountTrailingZeroes32, but for 64-bit numbers. */
 inline uint_fast8_t
 CountTrailingZeroes64(uint64_t u)
 {
   MOZ_ASSERT(u != 0);
   return detail::CountTrailingZeroes64(u);
 }
 namespace detail {
 template<typename T, size_t Size = sizeof(T)>
 class CeilingLog2;
 template<typename T>
 class CeilingLog2<T, 4>
 {
   public:
     static uint_fast8_t compute(const T t) {
       // Check for <= 1 to avoid the == 0 undefined case.
       return t <= 1 ? 0 : 32 - CountLeadingZeroes32(t - 1);
     }
 };
 template<typename T>
 class CeilingLog2<T, 8>
 {
   public:
     static uint_fast8_t compute(const T t) {
       // Check for <= 1 to avoid the == 0 undefined case.
       return t <= 1 ? 0 : 64 - CountLeadingZeroes64(t - 1);
     }
 };
 } // namespace detail
 /**
  * Compute the log of the least power of 2 greater than or equal to |t|.
  *
  * CeilingLog2(0..1) is 0;
  * CeilingLog2(2) is 1;
  * CeilingLog2(3..4) is 2;
  * CeilingLog2(5..8) is 3;
  * CeilingLog2(9..16) is 4; and so on.
  */
 template<typename T>
 inline uint_fast8_t
 CeilingLog2(const T t)
 {
   return detail::CeilingLog2<T>::compute(t);
 }
 /** A CeilingLog2 variant that accepts only size_t. */
 inline uint_fast8_t
 CeilingLog2Size(size_t n)
 {
   return CeilingLog2(n);
 }
 namespace detail {
 template<typename T, size_t Size = sizeof(T)>
 class FloorLog2;
 template<typename T>
 class FloorLog2<T, 4>
 {
   public:
     static uint_fast8_t compute(const T t) {
       return 31 - CountLeadingZeroes32(t | 1);
     }
 };
 template<typename T>
 class FloorLog2<T, 8>
 {
   public:
     static uint_fast8_t compute(const T t) {
       return 63 - CountLeadingZeroes64(t | 1);
     }
 };
 } // namespace detail
 /**
  * Compute the log of the greatest power of 2 less than or equal to |t|.
  *
  * FloorLog2(0..1) is 0;
  * FloorLog2(2..3) is 1;
  * FloorLog2(4..7) is 2;
  * FloorLog2(8..15) is 3; and so on.
  */
 template<typename T>
 inline uint_fast8_t
 FloorLog2(const T t)
 {
   return detail::FloorLog2<T>::compute(t);
 }
 /** A FloorLog2 variant that accepts only size_t. */
 inline uint_fast8_t
 FloorLog2Size(size_t n)
 {
   return FloorLog2(n);
 }
 /*
  * Compute the smallest power of 2 greater than or equal to |x|.  |x| must not
  * be so great that the computed value would overflow |size_t|.
  */
 inline size_t
 RoundUpPow2(size_t x)
 {
   MOZ_ASSERT(x <= (size_t(1) << (sizeof(size_t) * CHAR_BIT - 1)),
              "can't round up -- will overflow!");
   return size_t(1) << CeilingLog2(x);
 }
 /**
  * Rotates the bits of the given value left by the amount of the shift width.
  */
 template<typename T>
 inline T
 RotateLeft(const T t, uint_fast8_t shift)
 {
   MOZ_ASSERT(shift < sizeof(T) * CHAR_BIT, "Shift value is too large!");
   static_assert(IsUnsigned<T>::value, "Rotates require unsigned values");
   return (t << shift) | (t >> (sizeof(T) * CHAR_BIT - shift));
 }
 /**
  * Rotates the bits of the given value right by the amount of the shift width.
  */
 template<typename T>
 inline T
 RotateRight(const T t, uint_fast8_t shift)
 {
   MOZ_ASSERT(shift < sizeof(T) * CHAR_BIT, "Shift value is too large!");
   static_assert(IsUnsigned<T>::value, "Rotates require unsigned values");
   return (t >> shift) | (t << (sizeof(T) * CHAR_BIT - shift));
 }
 } /* namespace mozilla */
 #endif /* mozilla_MathAlgorithms_h */

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mfbt/MathAlgorithms.h@97036ab72558 (annotated)

mfbt/MathAlgorithms.h