text: /* -*- 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/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>
  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;
  }
  
  template<typename E, E N, typename T>
  MOZ_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>
  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 */
  