gecko-dev/mfbt/ArrayUtils.h

112 lines
2.7 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/Array.h"
namespace mozilla {
/*
* Safely subtract two pointers when it is known that end >= begin. This avoids
* the common compiler bug that if (size_t(end) - size_t(begin)) 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* begin, T* end)
{
MOZ_ASSERT(end >= begin);
return (size_t(end) - size_t(begin)) / 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 (&arr)[N])
{
return N;
}
template<typename T, size_t N>
MOZ_CONSTEXPR size_t
ArrayLength(const Array<T, N>& arr)
{
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 (&arr)[N])
{
return arr + ArrayLength(arr);
}
template<typename T, size_t N>
MOZ_CONSTEXPR T*
ArrayEnd(Array<T, N>& arr)
{
return &arr[0] + ArrayLength(arr);
}
template<typename T, size_t N>
MOZ_CONSTEXPR const T*
ArrayEnd(const Array<T, N>& arr)
{
return &arr[0] + ArrayLength(arr);
}
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 */