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1 : /* -*- Mode: C++; tab-width: 8; indent-tabs-mode: nil; c-basic-offset: 2 -*- */
2 : /* vim: set ts=8 sts=2 et sw=2 tw=80: */
3 : /* This Source Code Form is subject to the terms of the Mozilla Public
4 : * License, v. 2.0. If a copy of the MPL was not distributed with this
5 : * file, You can obtain one at http://mozilla.org/MPL/2.0/. */
6 :
7 : /*
8 : * Implements various helper functions related to arrays.
9 : */
10 :
11 : #ifndef mozilla_ArrayUtils_h
12 : #define mozilla_ArrayUtils_h
13 :
14 : #include "mozilla/Assertions.h"
15 : #include "mozilla/Attributes.h"
16 :
17 : #include <stddef.h>
18 :
19 : #ifdef __cplusplus
20 :
21 : #include "mozilla/Alignment.h"
22 : #include "mozilla/Array.h"
23 : #include "mozilla/EnumeratedArray.h"
24 : #include "mozilla/TypeTraits.h"
25 :
26 : namespace mozilla {
27 :
28 : /*
29 : * Safely subtract two pointers when it is known that aEnd >= aBegin, yielding a
30 : * size_t result.
31 : *
32 : * Ordinary pointer subtraction yields a ptrdiff_t result, which, being signed,
33 : * has insufficient range to express the distance between pointers at opposite
34 : * ends of the address space. Furthermore, most compilers use ptrdiff_t to
35 : * represent the intermediate byte address distance, before dividing by
36 : * sizeof(T); if that intermediate result overflows, they'll produce results
37 : * with the wrong sign even when the correct scaled distance would fit in a
38 : * ptrdiff_t.
39 : */
40 : template<class T>
41 : MOZ_ALWAYS_INLINE size_t
42 2568761 : PointerRangeSize(T* aBegin, T* aEnd)
43 : {
44 2568761 : MOZ_ASSERT(aEnd >= aBegin);
45 2568761 : return (size_t(aEnd) - size_t(aBegin)) / sizeof(T);
46 : }
47 :
48 : /*
49 : * Compute the length of an array with constant length. (Use of this method
50 : * with a non-array pointer will not compile.)
51 : *
52 : * Beware of the implicit trailing '\0' when using this with string constants.
53 : */
54 : template<typename T, size_t N>
55 : constexpr size_t
56 3245915 : ArrayLength(T (&aArr)[N])
57 : {
58 3245915 : return N;
59 : }
60 :
61 : template<typename T, size_t N>
62 : constexpr size_t
63 200 : ArrayLength(const Array<T, N>& aArr)
64 : {
65 200 : return N;
66 : }
67 :
68 : template<typename E, E N, typename T>
69 : constexpr size_t
70 0 : ArrayLength(const EnumeratedArray<E, N, T>& aArr)
71 : {
72 0 : return size_t(N);
73 : }
74 :
75 : /*
76 : * Compute the address one past the last element of a constant-length array.
77 : *
78 : * Beware of the implicit trailing '\0' when using this with string constants.
79 : */
80 : template<typename T, size_t N>
81 : constexpr T*
82 13960 : ArrayEnd(T (&aArr)[N])
83 : {
84 13960 : return aArr + ArrayLength(aArr);
85 : }
86 :
87 : template<typename T, size_t N>
88 : constexpr T*
89 : ArrayEnd(Array<T, N>& aArr)
90 : {
91 : return &aArr[0] + ArrayLength(aArr);
92 : }
93 :
94 : template<typename T, size_t N>
95 : constexpr const T*
96 : ArrayEnd(const Array<T, N>& aArr)
97 : {
98 : return &aArr[0] + ArrayLength(aArr);
99 : }
100 :
101 : namespace detail {
102 :
103 : template<typename AlignType, typename Pointee,
104 : typename = EnableIf<!IsVoid<AlignType>::value>>
105 : struct AlignedChecker
106 : {
107 : static void
108 : test(const Pointee* aPtr)
109 : {
110 : MOZ_ASSERT((uintptr_t(aPtr) % MOZ_ALIGNOF(AlignType)) == 0,
111 : "performing a range-check with a misaligned pointer");
112 : }
113 : };
114 :
115 : template<typename AlignType, typename Pointee>
116 : struct AlignedChecker<AlignType, Pointee>
117 : {
118 : static void
119 0 : test(const Pointee* aPtr)
120 : {
121 0 : }
122 : };
123 :
124 : } // namespace detail
125 :
126 : /**
127 : * Determines whether |aPtr| points at an object in the range [aBegin, aEnd).
128 : *
129 : * |aPtr| must have the same alignment as |aBegin| and |aEnd|. This usually
130 : * should be achieved by ensuring |aPtr| points at a |U|, not just that it
131 : * points at a |T|.
132 : *
133 : * It is a usage error for any argument to be misaligned.
134 : *
135 : * It's okay for T* to be void*, and if so U* may also be void*. In the latter
136 : * case no argument is required to be aligned (obviously, as void* implies no
137 : * particular alignment).
138 : */
139 : template<typename T, typename U>
140 : inline typename EnableIf<IsSame<T, U>::value ||
141 : IsBaseOf<T, U>::value ||
142 : IsVoid<T>::value,
143 : bool>::Type
144 0 : IsInRange(const T* aPtr, const U* aBegin, const U* aEnd)
145 : {
146 0 : MOZ_ASSERT(aBegin <= aEnd);
147 0 : detail::AlignedChecker<U, T>::test(aPtr);
148 0 : detail::AlignedChecker<U, U>::test(aBegin);
149 0 : detail::AlignedChecker<U, U>::test(aEnd);
150 0 : return aBegin <= reinterpret_cast<const U*>(aPtr) &&
151 0 : reinterpret_cast<const U*>(aPtr) < aEnd;
152 : }
153 :
154 : /**
155 : * Convenience version of the above method when the valid range is specified as
156 : * uintptr_t values. As above, |aPtr| must be aligned, and |aBegin| and |aEnd|
157 : * must be aligned with respect to |T|.
158 : */
159 : template<typename T>
160 : inline bool
161 0 : IsInRange(const T* aPtr, uintptr_t aBegin, uintptr_t aEnd)
162 : {
163 0 : return IsInRange(aPtr,
164 : reinterpret_cast<const T*>(aBegin),
165 0 : reinterpret_cast<const T*>(aEnd));
166 : }
167 :
168 : namespace detail {
169 :
170 : /*
171 : * Helper for the MOZ_ARRAY_LENGTH() macro to make the length a typesafe
172 : * compile-time constant even on compilers lacking constexpr support.
173 : */
174 : template <typename T, size_t N>
175 : char (&ArrayLengthHelper(T (&array)[N]))[N];
176 :
177 : } /* namespace detail */
178 :
179 : } /* namespace mozilla */
180 :
181 : #endif /* __cplusplus */
182 :
183 : /*
184 : * MOZ_ARRAY_LENGTH() is an alternative to mozilla::ArrayLength() for C files
185 : * that can't use C++ template functions and for static_assert() calls that
186 : * can't call ArrayLength() when it is not a C++11 constexpr function.
187 : */
188 : #ifdef __cplusplus
189 : # define MOZ_ARRAY_LENGTH(array) sizeof(mozilla::detail::ArrayLengthHelper(array))
190 : #else
191 : # define MOZ_ARRAY_LENGTH(array) (sizeof(array)/sizeof((array)[0]))
192 : #endif
193 :
194 : #endif /* mozilla_ArrayUtils_h */
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