gecko-dev/mfbt/ArrayUtils.h
Nicholas Nethercote 2a0942be41 Bug 1036789 - Convert the third quarter of MFBT to Gecko style. r=Ms2ger.
--HG--
extra : rebase_source : 668cd394806203ddfa34bd4f226335ff26c846b5
2014-07-10 19:10:17 -07:00

178 lines
4.6 KiB
C++

/* -*- 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>
#ifdef __cplusplus
#include "mozilla/Alignment.h"
#include "mozilla/Array.h"
#include "mozilla/TypeTraits.h"
namespace mozilla {
/*
* Safely subtract two pointers when it is known that aEnd >= aBegin. This
* avoids the common compiler bug that if (size_t(aEnd) - size_t(aBegin)) has
* the MSB set, the unsigned subtraction followed by right shift will produce
* -1, or size_t(-1), instead of the real difference.
*/
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>
MOZ_CONSTEXPR size_t
ArrayLength(T (&aArr)[N])
{
return N;
}
template<typename T, size_t N>
MOZ_CONSTEXPR size_t
ArrayLength(const Array<T, N>& aArr)
{
return 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>
MOZ_CONSTEXPR T*
ArrayEnd(T (&aArr)[N])
{
return aArr + ArrayLength(aArr);
}
template<typename T, size_t N>
MOZ_CONSTEXPR T*
ArrayEnd(Array<T, N>& aArr)
{
return &aArr[0] + ArrayLength(aArr);
}
template<typename T, size_t N>
MOZ_CONSTEXPR const T*
ArrayEnd(const Array<T, N>& aArr)
{
return &aArr[0] + ArrayLength(aArr);
}
namespace detail {
template<typename AlignType, typename Pointee>
struct AlignedChecker
{
static void
test(Pointee* aPtr)
{
MOZ_ASSERT((uintptr_t(aPtr) % MOZ_ALIGNOF(AlignType)) == 0,
"performing a range-check with a misaligned pointer");
}
};
template<typename Pointee>
struct AlignedChecker<void, Pointee>
{
static void
test(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 typename EnableIf<IsSame<T, U>::value ||
IsBaseOf<T, U>::value ||
IsVoid<T>::value,
bool>::Type
IsInRange(T* aPtr, U* aBegin, 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 <= static_cast<U*>(aPtr) && static_cast<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(T* aPtr, uintptr_t aBegin, uintptr_t aEnd)
{
return IsInRange(aPtr,
reinterpret_cast<T*>(aBegin), reinterpret_cast<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 */