mfbt/ArrayUtils.h
author Boris Zbarsky <bzbarsky@mit.edu>
Wed, 24 Jun 2015 00:42:46 -0700
changeset 250045 4267b74ee795e8127ffce4d45d00384cd8170130
parent 240614 9d2b8afeb3b43c97d76789cd413a226d87e19b24
child 268400 c24e66d011eca8cf40bd5e48bacc804e429652c3
permissions -rw-r--r--
Bug 1176083. Remove the now-dead code for the XPCOM version of setTimeout/setInterval. r=smaug I claim this code is dead because on the one hand it's no longer called from JS (because Window is always on WebIDL bindings, but on the other hand it can't really be called from C++ because it depends on examining the XPConnect call information. I think removing this completely, including from the IDL, is safe, because nothing directly returns nsIDOMJSWindow, so anyone using its vtable would have to QI to it and we're changing the IID.

/* -*- 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, 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>
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,
         typename = EnableIf<!IsVoid<AlignType>::value>>
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>
{
  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 typename EnableIf<IsSame<T, U>::value ||
                         IsBaseOf<T, U>::value ||
                         IsVoid<T>::value,
                         bool>::Type
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 */