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/* -*- Mode: C++; tab-width: 2; indent-tabs-mode: nil; c-basic-offset: 2 -*- */
/* 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/StandardInteger.h"
#include "mozilla/TypeTraits.h"
#include <cmath>
#include <limits.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 */
#endif /* mozilla_MathAlgorithms_h_ */
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