mirror of
https://github.com/mozilla/gecko-dev.git
synced 2024-10-31 22:25:30 +00:00
122 lines
3.5 KiB
C++
122 lines
3.5 KiB
C++
/* -*- 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 <limits.h>
|
|
#include <math.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 {
|
|
|
|
// 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 SupportedForAbsFixed : FalseType {};
|
|
|
|
template<> struct SupportedForAbsFixed<int8_t> : TrueType {};
|
|
template<> struct SupportedForAbsFixed<int16_t> : TrueType {};
|
|
template<> struct SupportedForAbsFixed<int32_t> : TrueType {};
|
|
template<> struct SupportedForAbsFixed<int64_t> : TrueType {};
|
|
|
|
template<typename T>
|
|
struct SupportedForAbs : SupportedForAbsFixed<T> {};
|
|
|
|
template<> struct SupportedForAbs<char> : IntegralConstant<bool, char(-1) < char(0)> {};
|
|
template<> struct SupportedForAbs<signed char> : TrueType {};
|
|
template<> struct SupportedForAbs<short> : TrueType {};
|
|
template<> struct SupportedForAbs<int> : TrueType {};
|
|
template<> struct SupportedForAbs<long> : TrueType {};
|
|
template<> struct SupportedForAbs<long long> : TrueType {};
|
|
template<> struct SupportedForAbs<float> : TrueType {};
|
|
template<> struct SupportedForAbs<double> : TrueType {};
|
|
template<> struct SupportedForAbs<long double> : TrueType {};
|
|
|
|
} // namespace detail
|
|
|
|
template<typename T>
|
|
inline typename mozilla::EnableIf<detail::SupportedForAbs<T>::value, T>::Type
|
|
Abs(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;
|
|
}
|
|
|
|
template<>
|
|
inline float
|
|
Abs<float>(const float f)
|
|
{
|
|
return fabsf(f);
|
|
}
|
|
|
|
template<>
|
|
inline double
|
|
Abs<double>(const double d)
|
|
{
|
|
return fabs(d);
|
|
}
|
|
|
|
template<>
|
|
inline long double
|
|
Abs<long double>(const long double d)
|
|
{
|
|
return fabsl(d);
|
|
}
|
|
|
|
} /* namespace mozilla */
|
|
|
|
#endif /* mozilla_MathAlgorithms_h_ */
|