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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
* file, You can obtain one at http://mozilla.org/MPL/2.0/. */
/*
* Implements various helper functions related to arrays.
*/
#ifndef mozilla_ArrayUtils_h
#define mozilla_ArrayUtils_h
#include "mozilla/Assertions.h"
#include "mozilla/Attributes.h"
#include <stddef.h>
#include <stdint.h>
#ifdef __cplusplus
# include <algorithm>
# include <type_traits>
# include "mozilla/Alignment.h"
namespace mozilla {
template <typename T, size_t Length>
class Array;
template <typename IndexType, IndexType SizeAsEnumValue, typename ValueType>
class EnumeratedArray;
/*
* Safely subtract two pointers when it is known that aEnd >= aBegin, yielding a
* size_t result.
*
* Ordinary pointer subtraction yields a ptrdiff_t result, which, being signed,
* has insufficient range to express the distance between pointers at opposite
* ends of the address space. Furthermore, most compilers use ptrdiff_t to
* represent the intermediate byte address distance, before dividing by
* sizeof(T); if that intermediate result overflows, they'll produce results
* with the wrong sign even when the correct scaled distance would fit in a
* ptrdiff_t.
*/
template <class T>
MOZ_ALWAYS_INLINE size_t PointerRangeSize(T* aBegin, T* aEnd) {
MOZ_ASSERT(aEnd >= aBegin);
return (size_t(aEnd) - size_t(aBegin)) / sizeof(T);
}
/*
* Compute the length of an array with constant length. (Use of this method
* with a non-array pointer will not compile.)
*
* Beware of the implicit trailing '\0' when using this with string constants.
*/
template <typename T, size_t N>
constexpr size_t ArrayLength(T (&aArr)[N]) {
return N;
}
template <typename T, size_t N>
constexpr size_t ArrayLength(const Array<T, N>& aArr) {
return N;
}
template <typename E, E N, typename T>
constexpr size_t ArrayLength(const EnumeratedArray<E, N, T>& aArr) {
return size_t(N);
}
/*
* Compute the address one past the last element of a constant-length array.
*
* Beware of the implicit trailing '\0' when using this with string constants.
*/
template <typename T, size_t N>
constexpr T* ArrayEnd(T (&aArr)[N]) {
return aArr + ArrayLength(aArr);
}
template <typename T, size_t N>
constexpr T* ArrayEnd(Array<T, N>& aArr) {
return &aArr[0] + ArrayLength(aArr);
}
template <typename T, size_t N>
constexpr const T* ArrayEnd(const Array<T, N>& aArr) {
return &aArr[0] + ArrayLength(aArr);
}
/**
* std::equal has subpar ergonomics.
*/
template <typename T, typename U, size_t N>
bool ArrayEqual(const T (&a)[N], const U (&b)[N]) {
return std::equal(a, a + N, b);
}
template <typename T, typename U>
bool ArrayEqual(const T* const a, const U* const b, const size_t n) {
return std::equal(a, a + n, b);
}
namespace detail {
template <typename AlignType, typename Pointee, typename = void>
struct AlignedChecker {
static void test(const Pointee* aPtr) {
MOZ_ASSERT((uintptr_t(aPtr) % MOZ_ALIGNOF(AlignType)) == 0,
"performing a range-check with a misaligned pointer");
}
};
template <typename AlignType, typename Pointee>
struct AlignedChecker<AlignType, Pointee,
std::enable_if_t<std::is_void_v<AlignType>>> {
static void test(const Pointee* aPtr) {}
};
} // namespace detail
/**
* Determines whether |aPtr| points at an object in the range [aBegin, aEnd).
*
* |aPtr| must have the same alignment as |aBegin| and |aEnd|. This usually
* should be achieved by ensuring |aPtr| points at a |U|, not just that it
* points at a |T|.
*
* It is a usage error for any argument to be misaligned.
*
* It's okay for T* to be void*, and if so U* may also be void*. In the latter
* case no argument is required to be aligned (obviously, as void* implies no
* particular alignment).
*/
template <typename T, typename U>
inline std::enable_if_t<std::is_same_v<T, U> || std::is_base_of<T, U>::value ||
std::is_void_v<T>,
bool>
IsInRange(const T* aPtr, const U* aBegin, const U* aEnd) {
MOZ_ASSERT(aBegin <= aEnd);
detail::AlignedChecker<U, T>::test(aPtr);
detail::AlignedChecker<U, U>::test(aBegin);
detail::AlignedChecker<U, U>::test(aEnd);
return aBegin <= reinterpret_cast<const U*>(aPtr) &&
reinterpret_cast<const U*>(aPtr) < aEnd;
}
/**
* Convenience version of the above method when the valid range is specified as
* uintptr_t values. As above, |aPtr| must be aligned, and |aBegin| and |aEnd|
* must be aligned with respect to |T|.
*/
template <typename T>
inline bool IsInRange(const T* aPtr, uintptr_t aBegin, uintptr_t aEnd) {
return IsInRange(aPtr, reinterpret_cast<const T*>(aBegin),
reinterpret_cast<const T*>(aEnd));
}
namespace detail {
/*
* Helper for the MOZ_ARRAY_LENGTH() macro to make the length a typesafe
* compile-time constant even on compilers lacking constexpr support.
*/
template <typename T, size_t N>
char (&ArrayLengthHelper(T (&array)[N]))[N];
} /* namespace detail */
} /* namespace mozilla */
#endif /* __cplusplus */
/*
* MOZ_ARRAY_LENGTH() is an alternative to mozilla::ArrayLength() for C files
* that can't use C++ template functions and for static_assert() calls that
* can't call ArrayLength() when it is not a C++11 constexpr function.
*/
#ifdef __cplusplus
# define MOZ_ARRAY_LENGTH(array) \
sizeof(mozilla::detail::ArrayLengthHelper(array))
#else
# define MOZ_ARRAY_LENGTH(array) (sizeof(array) / sizeof((array)[0]))
#endif
#endif /* mozilla_ArrayUtils_h */
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