mfbt/MathAlgorithms.h
author Masayuki Nakano <masayuki@d-toybox.com>
Thu, 16 Mar 2017 16:26:43 +0900
changeset 398554 8e72178c3893c377972209cccd2e561e1ec06c7d
parent 363205 250c433640e0c13087189284a7f38285bb3a85c9
child 456071 e266383ee349457626c646694a374d9d3ef7bc19
permissions -rw-r--r--
Bug 1339331 TextEventDispatcher should replace \r in composition string with \n and TextComposition should allow to input \n with composition events r=m_kato According to ATOK's behavior, IME may send different line breaker from its platform's standard. Therefore, we should treat \r as \n too. Additionally, currently, TextComposition doesn't allow to input \n with composition. However, this was added for preventing to see odd control characters as boxes with code point. Therefore, we should allow \n for IMEs. (It was allowed, this limitation is unexpected when I reviewed the patch to reject control characters in TextComposition.) MozReview-Commit-ID: DzGSMgp89Av

/* -*- 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 aA, IntegerType aB)
{
  // 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(aA > IntegerType(0));
  MOZ_ASSERT(aB > IntegerType(0));

  while (aA != aB) {
    if (aA > aB) {
      aA = aA - aB;
    } else {
      aB = aB - aA;
    }
  }

  return aA;
}

// Least Common Multiple
template<typename IntegerType>
MOZ_ALWAYS_INLINE IntegerType
EuclidLCM(IntegerType aA, IntegerType aB)
{
  // Divide first to reduce overflow risk.
  return (aA / EuclidGCD(aA, aB)) * aB;
}

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 aValue)
{
  // 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(aValue >= 0 ||
             -(aValue + 1) != T((1ULL << (CHAR_BIT * sizeof(T) - 1)) - 1),
             "You can't negate the smallest possible negative integer!");
  return aValue >= 0 ? aValue : -aValue;
}

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 aValue)
{
  typedef typename detail::AbsReturnType<T>::Type ReturnType;
  return aValue >= 0 ? ReturnType(aValue) : ~ReturnType(aValue) + 1;
}

template<>
inline float
Abs<float>(const float aFloat)
{
  return std::fabs(aFloat);
}

template<>
inline double
Abs<double>(const double aDouble)
{
  return std::fabs(aDouble);
}

template<>
inline long double
Abs<long double>(const long double aLongDouble)
{
  return std::fabs(aLongDouble);
}

} // namespace mozilla

#if defined(_MSC_VER) && \
    (defined(_M_IX86) || defined(_M_AMD64) || defined(_M_X64))
#  define MOZ_BITSCAN_WINDOWS

#  include <intrin.h>
#  pragma intrinsic(_BitScanForward, _BitScanReverse)

#  if defined(_M_AMD64) || defined(_M_X64)
#    define MOZ_BITSCAN_WINDOWS64
#   pragma intrinsic(_BitScanForward64, _BitScanReverse64)
#  endif

#endif

namespace mozilla {

namespace detail {

#if defined(MOZ_BITSCAN_WINDOWS)

inline uint_fast8_t
CountLeadingZeroes32(uint32_t aValue)
{
  unsigned long index;
  if (!_BitScanReverse(&index, static_cast<unsigned long>(aValue)))
      return 32;
  return uint_fast8_t(31 - index);
}


inline uint_fast8_t
CountTrailingZeroes32(uint32_t aValue)
{
  unsigned long index;
  if (!_BitScanForward(&index, static_cast<unsigned long>(aValue)))
      return 32;
  return uint_fast8_t(index);
}

inline uint_fast8_t
CountPopulation32(uint32_t aValue)
{
  uint32_t x = aValue - ((aValue >> 1) & 0x55555555);
  x = (x & 0x33333333) + ((x >> 2) & 0x33333333);
  return (((x + (x >> 4)) & 0xf0f0f0f) * 0x1010101) >> 24;
}
inline uint_fast8_t
CountPopulation64(uint64_t aValue)
{
  return uint_fast8_t(CountPopulation32(aValue & 0xffffffff) +
                      CountPopulation32(aValue >> 32));
}

inline uint_fast8_t
CountLeadingZeroes64(uint64_t aValue)
{
#if defined(MOZ_BITSCAN_WINDOWS64)
  unsigned long index;
  if (!_BitScanReverse64(&index, static_cast<unsigned __int64>(aValue)))
      return 64;
  return uint_fast8_t(63 - index);
#else
  uint32_t hi = uint32_t(aValue >> 32);
  if (hi != 0) {
    return CountLeadingZeroes32(hi);
  }
  return 32u + CountLeadingZeroes32(uint32_t(aValue));
#endif
}

inline uint_fast8_t
CountTrailingZeroes64(uint64_t aValue)
{
#if defined(MOZ_BITSCAN_WINDOWS64)
  unsigned long index;
  if (!_BitScanForward64(&index, static_cast<unsigned __int64>(aValue)))
      return 64;
  return uint_fast8_t(index);
#else
  uint32_t lo = uint32_t(aValue);
  if (lo != 0) {
    return CountTrailingZeroes32(lo);
  }
  return 32u + CountTrailingZeroes32(uint32_t(aValue >> 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 aValue)
{
  return __builtin_clz(aValue);
}

inline uint_fast8_t
CountTrailingZeroes32(uint32_t aValue)
{
  return __builtin_ctz(aValue);
}

inline uint_fast8_t
CountPopulation32(uint32_t aValue)
{
  return __builtin_popcount(aValue);
}

inline uint_fast8_t
CountPopulation64(uint64_t aValue)
{
  return __builtin_popcountll(aValue);
}

inline uint_fast8_t
CountLeadingZeroes64(uint64_t aValue)
{
  return __builtin_clzll(aValue);
}

inline uint_fast8_t
CountTrailingZeroes64(uint64_t aValue)
{
  return __builtin_ctzll(aValue);
}

#else
#  error "Implement these!"
inline uint_fast8_t CountLeadingZeroes32(uint32_t aValue) = delete;
inline uint_fast8_t CountTrailingZeroes32(uint32_t aValue) = delete;
inline uint_fast8_t CountPopulation32(uint32_t aValue) = delete;
inline uint_fast8_t CountPopulation64(uint64_t aValue) = delete;
inline uint_fast8_t CountLeadingZeroes64(uint64_t aValue) = delete;
inline uint_fast8_t CountTrailingZeroes64(uint64_t aValue) = delete;
#endif

} // namespace detail

/**
 * Compute the number of high-order zero bits in the NON-ZERO number |aValue|.
 * 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 aValue)
{
  MOZ_ASSERT(aValue != 0);
  return detail::CountLeadingZeroes32(aValue);
}

/**
 * Compute the number of low-order zero bits in the NON-ZERO number |aValue|.
 * 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 aValue)
{
  MOZ_ASSERT(aValue != 0);
  return detail::CountTrailingZeroes32(aValue);
}

/**
 * Compute the number of one bits in the number |aValue|,
 */
inline uint_fast8_t
CountPopulation32(uint32_t aValue)
{
  return detail::CountPopulation32(aValue);
}

/** Analogous to CountPopulation32, but for 64-bit numbers */
inline uint_fast8_t
CountPopulation64(uint64_t aValue)
{
  return detail::CountPopulation64(aValue);
}

/** Analogous to CountLeadingZeroes32, but for 64-bit numbers. */
inline uint_fast8_t
CountLeadingZeroes64(uint64_t aValue)
{
  MOZ_ASSERT(aValue != 0);
  return detail::CountLeadingZeroes64(aValue);
}

/** Analogous to CountTrailingZeroes32, but for 64-bit numbers. */
inline uint_fast8_t
CountTrailingZeroes64(uint64_t aValue)
{
  MOZ_ASSERT(aValue != 0);
  return detail::CountTrailingZeroes64(aValue);
}

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 aValue)
  {
    // Check for <= 1 to avoid the == 0 undefined case.
    return aValue <= 1 ? 0u : 32u - CountLeadingZeroes32(aValue - 1);
  }
};

template<typename T>
class CeilingLog2<T, 8>
{
public:
  static uint_fast8_t compute(const T aValue)
  {
    // Check for <= 1 to avoid the == 0 undefined case.
    return aValue <= 1 ? 0u : 64u - CountLeadingZeroes64(aValue - 1);
  }
};

} // namespace detail

/**
 * Compute the log of the least power of 2 greater than or equal to |aValue|.
 *
 * 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 aValue)
{
  return detail::CeilingLog2<T>::compute(aValue);
}

/** A CeilingLog2 variant that accepts only size_t. */
inline uint_fast8_t
CeilingLog2Size(size_t aValue)
{
  return CeilingLog2(aValue);
}

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 aValue)
  {
    return 31u - CountLeadingZeroes32(aValue | 1);
  }
};

template<typename T>
class FloorLog2<T, 8>
{
public:
  static uint_fast8_t compute(const T aValue)
  {
    return 63u - CountLeadingZeroes64(aValue | 1);
  }
};

} // namespace detail

/**
 * Compute the log of the greatest power of 2 less than or equal to |aValue|.
 *
 * 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 aValue)
{
  return detail::FloorLog2<T>::compute(aValue);
}

/** A FloorLog2 variant that accepts only size_t. */
inline uint_fast8_t
FloorLog2Size(size_t aValue)
{
  return FloorLog2(aValue);
}

/*
 * 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 aValue)
{
  MOZ_ASSERT(aValue <= (size_t(1) << (sizeof(size_t) * CHAR_BIT - 1)),
             "can't round up -- will overflow!");
  return size_t(1) << CeilingLog2(aValue);
}

/**
 * Rotates the bits of the given value left by the amount of the shift width.
 */
template<typename T>
inline T
RotateLeft(const T aValue, uint_fast8_t aShift)
{
  MOZ_ASSERT(aShift < sizeof(T) * CHAR_BIT, "Shift value is too large!");
  MOZ_ASSERT(aShift > 0,
             "Rotation by value length is undefined behavior, but compilers "
             "do not currently fold a test into the rotate instruction. "
             "Please remove this restriction when compilers optimize the "
             "zero case (http://blog.regehr.org/archives/1063).");
  static_assert(IsUnsigned<T>::value, "Rotates require unsigned values");
  return (aValue << aShift) | (aValue >> (sizeof(T) * CHAR_BIT - aShift));
}

/**
 * Rotates the bits of the given value right by the amount of the shift width.
 */
template<typename T>
inline T
RotateRight(const T aValue, uint_fast8_t aShift)
{
  MOZ_ASSERT(aShift < sizeof(T) * CHAR_BIT, "Shift value is too large!");
  MOZ_ASSERT(aShift > 0,
             "Rotation by value length is undefined behavior, but compilers "
             "do not currently fold a test into the rotate instruction. "
             "Please remove this restriction when compilers optimize the "
             "zero case (http://blog.regehr.org/archives/1063).");
  static_assert(IsUnsigned<T>::value, "Rotates require unsigned values");
  return (aValue >> aShift) | (aValue << (sizeof(T) * CHAR_BIT - aShift));
}

/**
 * Returns true if |x| is a power of two.
 * Zero is not an integer power of two. (-Inf is not an integer)
 */
template<typename T>
constexpr bool
IsPowerOfTwo(T x)
{
    static_assert(IsUnsigned<T>::value,
                  "IsPowerOfTwo requires unsigned values");
    return x && (x & (x - 1)) == 0;
}

template<typename T>
inline T
Clamp(const T aValue, const T aMin, const T aMax)
{
    static_assert(IsIntegral<T>::value,
                  "Clamp accepts only integral types, so that it doesn't have"
                  " to distinguish differently-signed zeroes (which users may"
                  " or may not care to distinguish, likely at a perf cost) or"
                  " to decide how to clamp NaN or a range with a NaN"
                  " endpoint.");
    MOZ_ASSERT(aMin <= aMax);

    if (aValue <= aMin)
        return aMin;
    if (aValue >= aMax)
        return aMax;
    return aValue;
}

} /* namespace mozilla */

#endif /* mozilla_MathAlgorithms_h */