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/* -*- 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
#ifndef Utils_h
#define Utils_h
#include <cstring>
#include <type_traits>
#ifdef XP_WIN
# include <io.h> // for _write()
#endif
#include "mozilla/CheckedInt.h"
#include "mozilla/TemplateLib.h"
// Helper for log2 of powers of 2 at compile time.
template <size_t N>
struct Log2 : mozilla::tl::CeilingLog2<N> {
using mozilla::tl::CeilingLog2<N>::value;
static_assert(1ULL << value == N, "Number is not a power of 2");
};
#define LOG2(N) Log2<N>::value
enum class Order {
eLess = -1,
eEqual = 0,
eGreater = 1,
};
// Compare two integers. Returns whether the first integer is Less,
// Equal or Greater than the second integer.
template <typename T>
Order CompareInt(T aValue1, T aValue2) {
static_assert(std::is_integral_v<T>, "Type must be integral");
if (aValue1 < aValue2) {
return Order::eLess;
}
if (aValue1 > aValue2) {
return Order::eGreater;
}
return Order::eEqual;
}
// Compare two addresses. Returns whether the first address is Less,
// Equal or Greater than the second address.
template <typename T>
Order CompareAddr(T* aAddr1, T* aAddr2) {
return CompareInt(uintptr_t(aAddr1), uintptr_t(aAddr2));
}
// Helper for (fast) comparison of fractions without involving divisions or
// floats.
class Fraction {
public:
explicit constexpr Fraction(size_t aNumerator, size_t aDenominator)
: mNumerator(aNumerator), mDenominator(aDenominator) {}
MOZ_IMPLICIT constexpr Fraction(long double aValue)
// We use an arbitrary power of two as denominator that provides enough
// precision for our use case.
: mNumerator(aValue * 4096), mDenominator(4096) {}
inline bool operator<(const Fraction& aOther) const {
#ifndef MOZ_DEBUG
// We are comparing A / B < C / D, with all A, B, C and D being positive
// numbers. Multiplying both sides with B * D, we have:
// (A * B * D) / B < (C * B * D) / D, which can then be simplified as
// A * D < C * B. When can thus compare our fractions without actually
// doing any division.
// This however assumes the multiplied quantities are small enough not
// to overflow the multiplication. We use CheckedInt on debug builds
// to enforce the assumption.
return mNumerator * aOther.mDenominator < aOther.mNumerator * mDenominator;
#else
mozilla::CheckedInt<size_t> numerator(mNumerator);
mozilla::CheckedInt<size_t> denominator(mDenominator);
// value() asserts when the multiplication overflowed.
size_t lhs = (numerator * aOther.mDenominator).value();
size_t rhs = (aOther.mNumerator * denominator).value();
return lhs < rhs;
#endif
}
inline bool operator>(const Fraction& aOther) const { return aOther < *this; }
inline bool operator>=(const Fraction& aOther) const {
return !(*this < aOther);
}
inline bool operator<=(const Fraction& aOther) const {
return !(*this > aOther);
}
inline bool operator==(const Fraction& aOther) const {
#ifndef MOZ_DEBUG
// Same logic as operator<
return mNumerator * aOther.mDenominator == aOther.mNumerator * mDenominator;
#else
mozilla::CheckedInt<size_t> numerator(mNumerator);
mozilla::CheckedInt<size_t> denominator(mDenominator);
size_t lhs = (numerator * aOther.mDenominator).value();
size_t rhs = (aOther.mNumerator * denominator).value();
return lhs == rhs;
#endif
}
inline bool operator!=(const Fraction& aOther) const {
return !(*this == aOther);
}
private:
size_t mNumerator;
size_t mDenominator;
};
// Fast division
//
// During deallocation we want to divide by the size class. This class
// provides a routine and sets up a constant as follows.
//
// To divide by a number D that is not a power of two we multiply by (2^17 /
// D) and then right shift by 17 positions.
//
// X / D
//
// becomes
//
// (X * m) >> p
//
// Where m is calculated during the FastDivisor constructor similarly to:
//
// m = 2^p / D
//
template <typename T>
class FastDivisor {
private:
// The shift amount (p) is chosen to minimise the size of m while
// working for divisors up to 65536 in steps of 16. I arrived at 17
// experimentally. I wanted a low number to minimise the range of m
// so it can fit in a uint16_t, 16 didn't work but 17 worked perfectly.
//
// We'd need to increase this if we allocated memory on smaller boundaries
// than 16.
static const unsigned p = 17;
// We can fit the inverted divisor in 16 bits, but we template it here for
// convenience.
T m;
public:
// Needed so mBins can be constructed.
FastDivisor() : m(0) {}
FastDivisor(unsigned div, unsigned max) {
MOZ_ASSERT(div <= max);
// divide_inv_shift is large enough.
MOZ_ASSERT((1U << p) >= div);
// The calculation here for m is formula 26 from Section
// 10-9 "Unsigned Division by Divisors >= 1" in
// Henry S. Warren, Jr.'s Hacker's Delight, 2nd Ed.
unsigned m_ = ((1U << p) + div - 1 - (((1U << p) - 1) % div)) / div;
// Make sure that max * m does not overflow.
MOZ_DIAGNOSTIC_ASSERT(max < UINT_MAX / m_);
MOZ_ASSERT(m_ <= std::numeric_limits<T>::max());
m = static_cast<T>(m_);
// Initialisation made m non-zero.
MOZ_ASSERT(m);
// Test that all the divisions in the range we expected would work.
#ifdef MOZ_DEBUG
for (unsigned num = 0; num < max; num += div) {
MOZ_ASSERT(num / div == divide(num));
}
#endif
}
// Note that this always occurs in uint32_t regardless of m's type. If m is
// a uint16_t it will be zero-extended before the multiplication. We also use
// uint32_t rather than something that could possibly be larger because it is
// most-likely the cheapest multiplication.
inline uint32_t divide(uint32_t num) const {
// Check that m was initialised.
MOZ_ASSERT(m);
return (num * m) >> p;
}
};
template <typename T>
unsigned inline operator/(unsigned num, FastDivisor<T> divisor) {
return divisor.divide(num);
}
// Return the offset between a and the nearest aligned address at or below a.
#define ALIGNMENT_ADDR2OFFSET(a, alignment) \
((size_t)((uintptr_t)(a) & ((alignment) - 1)))
// Return the smallest alignment multiple that is >= s.
#define ALIGNMENT_CEILING(s, alignment) \
(((s) + ((alignment) - 1)) & (~((alignment) - 1)))
static inline const char* _getprogname(void) { return "<jemalloc>"; }
#ifdef XP_WIN
# define STDERR_FILENO 2
#else
# define _write write
#endif
inline void _malloc_message(const char* p) {
// Pretend to check _write() errors to suppress gcc warnings about
// warn_unused_result annotations in some versions of glibc headers.
if (_write(STDERR_FILENO, p, (unsigned int)strlen(p)) < 0) {
return;
}
}
template <typename... Args>
static void _malloc_message(const char* p, Args... args) {
_malloc_message(p);
_malloc_message(args...);
}
#endif