mirror of
https://github.com/mozilla/gecko-dev.git
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184 lines
4.8 KiB
C++
184 lines
4.8 KiB
C++
/* -*- Mode: C++; tab-width: 8; indent-tabs-mode: nil; c-basic-offset: 2 -*- */
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/* vim: set ts=8 sts=2 et sw=2 tw=80: */
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/* This Source Code Form is subject to the terms of the Mozilla Public
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* License, v. 2.0. If a copy of the MPL was not distributed with this
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* file, You can obtain one at http://mozilla.org/MPL/2.0/. */
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/*
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* Implements various helper functions related to arrays.
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*/
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#ifndef mozilla_ArrayUtils_h
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#define mozilla_ArrayUtils_h
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#include "mozilla/Assertions.h"
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#include "mozilla/Attributes.h"
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#include <stddef.h>
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#ifdef __cplusplus
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#include "mozilla/Alignment.h"
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#include "mozilla/Array.h"
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#include "mozilla/TypeTraits.h"
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namespace mozilla {
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/*
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* Safely subtract two pointers when it is known that aEnd >= aBegin, yielding a
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* size_t result.
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*
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* Ordinary pointer subtraction yields a ptrdiff_t result, which, being signed,
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* has insufficient range to express the distance between pointers at opposite
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* ends of the address space. Furthermore, most compilers use ptrdiff_t to
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* represent the intermediate byte address distance, before dividing by
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* sizeof(T); if that intermediate result overflows, they'll produce results
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* with the wrong sign even when the correct scaled distance would fit in a
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* ptrdiff_t.
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*/
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template<class T>
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MOZ_ALWAYS_INLINE size_t
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PointerRangeSize(T* aBegin, T* aEnd)
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{
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MOZ_ASSERT(aEnd >= aBegin);
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return (size_t(aEnd) - size_t(aBegin)) / sizeof(T);
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}
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/*
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* Compute the length of an array with constant length. (Use of this method
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* with a non-array pointer will not compile.)
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*
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* Beware of the implicit trailing '\0' when using this with string constants.
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*/
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template<typename T, size_t N>
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MOZ_CONSTEXPR size_t
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ArrayLength(T (&aArr)[N])
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{
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return N;
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}
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template<typename T, size_t N>
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MOZ_CONSTEXPR size_t
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ArrayLength(const Array<T, N>& aArr)
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{
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return N;
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}
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/*
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* Compute the address one past the last element of a constant-length array.
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*
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* Beware of the implicit trailing '\0' when using this with string constants.
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*/
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template<typename T, size_t N>
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MOZ_CONSTEXPR T*
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ArrayEnd(T (&aArr)[N])
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{
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return aArr + ArrayLength(aArr);
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}
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template<typename T, size_t N>
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MOZ_CONSTEXPR T*
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ArrayEnd(Array<T, N>& aArr)
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{
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return &aArr[0] + ArrayLength(aArr);
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}
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template<typename T, size_t N>
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MOZ_CONSTEXPR const T*
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ArrayEnd(const Array<T, N>& aArr)
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{
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return &aArr[0] + ArrayLength(aArr);
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}
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namespace detail {
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template<typename AlignType, typename Pointee>
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struct AlignedChecker
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{
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static void
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test(Pointee* aPtr)
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{
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MOZ_ASSERT((uintptr_t(aPtr) % MOZ_ALIGNOF(AlignType)) == 0,
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"performing a range-check with a misaligned pointer");
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}
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};
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template<typename Pointee>
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struct AlignedChecker<void, Pointee>
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{
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static void
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test(Pointee* aPtr)
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{
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}
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};
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} // namespace detail
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/**
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* Determines whether |aPtr| points at an object in the range [aBegin, aEnd).
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*
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* |aPtr| must have the same alignment as |aBegin| and |aEnd|. This usually
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* should be achieved by ensuring |aPtr| points at a |U|, not just that it
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* points at a |T|.
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*
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* It is a usage error for any argument to be misaligned.
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*
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* It's okay for T* to be void*, and if so U* may also be void*. In the latter
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* case no argument is required to be aligned (obviously, as void* implies no
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* particular alignment).
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*/
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template<typename T, typename U>
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inline typename EnableIf<IsSame<T, U>::value ||
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IsBaseOf<T, U>::value ||
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IsVoid<T>::value,
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bool>::Type
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IsInRange(T* aPtr, U* aBegin, U* aEnd)
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{
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MOZ_ASSERT(aBegin <= aEnd);
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detail::AlignedChecker<U, T>::test(aPtr);
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detail::AlignedChecker<U, U>::test(aBegin);
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detail::AlignedChecker<U, U>::test(aEnd);
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return aBegin <= static_cast<U*>(aPtr) && static_cast<U*>(aPtr) < aEnd;
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}
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/**
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* Convenience version of the above method when the valid range is specified as
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* uintptr_t values. As above, |aPtr| must be aligned, and |aBegin| and |aEnd|
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* must be aligned with respect to |T|.
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*/
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template<typename T>
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inline bool
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IsInRange(T* aPtr, uintptr_t aBegin, uintptr_t aEnd)
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{
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return IsInRange(aPtr,
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reinterpret_cast<T*>(aBegin), reinterpret_cast<T*>(aEnd));
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}
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namespace detail {
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/*
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* Helper for the MOZ_ARRAY_LENGTH() macro to make the length a typesafe
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* compile-time constant even on compilers lacking constexpr support.
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*/
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template <typename T, size_t N>
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char (&ArrayLengthHelper(T (&array)[N]))[N];
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} /* namespace detail */
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} /* namespace mozilla */
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#endif /* __cplusplus */
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/*
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* MOZ_ARRAY_LENGTH() is an alternative to mozilla::ArrayLength() for C files
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* that can't use C++ template functions and for static_assert() calls that
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* can't call ArrayLength() when it is not a C++11 constexpr function.
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*/
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#ifdef __cplusplus
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# define MOZ_ARRAY_LENGTH(array) sizeof(mozilla::detail::ArrayLengthHelper(array))
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#else
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# define MOZ_ARRAY_LENGTH(array) (sizeof(array)/sizeof((array)[0]))
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#endif
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#endif /* mozilla_ArrayUtils_h */
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