mfbt/ArrayUtils.h
author Bryce Van Dyk <bvandyk@mozilla.com>
Mon, 27 Aug 2018 16:25:54 +0000
changeset 488616 259675bd67f96acf1ae0f2ed6115de4331a94d32
parent 483934 cffca1854a032479d908982f97f88a4c18cb6015
child 505383 6f3709b3878117466168c40affa7bca0b60cf75b
permissions -rw-r--r--
Bug 1486502 - Add widevine CDM headers to third party paths, clang-format ignore. r=sylvestre We wish to keep the widevine headers in the same formatting as upstream to ease comparison and as we do not modify these files. This patch adds the existing headers, as well as another we anticipate pulling down for our next bump (content_decryption_module_proxy.h) to the ignored paths. These files are ignored individually rather than the whole directory they're in, as we also have Mozilla code in that dir. Differential Revision: https://phabricator.services.mozilla.com/D4347

/* -*- 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 <algorithm>
#include <stddef.h>

#ifdef __cplusplus

#include "mozilla/Alignment.h"
#include "mozilla/Array.h"
#include "mozilla/EnumeratedArray.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>
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 = 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 */