1 /*
2  * Copyright (C) 2015 The Android Open Source Project
3  *
4  * Licensed under the Apache License, Version 2.0 (the "License");
5  * you may not use this file except in compliance with the License.
6  * You may obtain a copy of the License at
7  *
8  *      http://www.apache.org/licenses/LICENSE-2.0
9  *
10  * Unless required by applicable law or agreed to in writing, software
11  * distributed under the License is distributed on an "AS IS" BASIS,
12  * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
13  * See the License for the specific language governing permissions and
14  * limitations under the License.
15  */
16 
17 #ifndef ART_LIBARTBASE_BASE_ARRAY_SLICE_H_
18 #define ART_LIBARTBASE_BASE_ARRAY_SLICE_H_
19 
20 #include "base/bit_utils.h"
21 #include "base/casts.h"
22 #include "base/iteration_range.h"
23 #include "stride_iterator.h"
24 
25 namespace art {
26 
27 // An ArraySlice is an abstraction over an array or a part of an array of a particular type. It does
28 // bounds checking and can be made from several common array-like structures in Art.
29 template <typename T>
30 class ArraySlice {
31  public:
32   using value_type = T;
33   using reference = T&;
34   using const_reference = const T&;
35   using pointer = T*;
36   using const_pointer = const T*;
37   using iterator = StrideIterator<T>;
38   using const_iterator = StrideIterator<const T>;
39   using reverse_iterator = std::reverse_iterator<iterator>;
40   using const_reverse_iterator = std::reverse_iterator<const_iterator>;
41   using difference_type = ptrdiff_t;
42   using size_type = size_t;
43 
44   // Create an empty array slice.
ArraySlice()45   ArraySlice() : array_(nullptr), size_(0), element_size_(0) {}
46 
47   // Create an array slice of the first 'length' elements of the array, with each element being
48   // element_size bytes long.
49   ArraySlice(T* array,
50              size_t length,
51              size_t element_size = sizeof(T))
array_(array)52       : array_(array),
53         size_(dchecked_integral_cast<uint32_t>(length)),
54         element_size_(element_size) {
55     DCHECK(array_ != nullptr || length == 0);
56   }
57 
58   // Iterators.
begin()59   iterator begin() { return iterator(&AtUnchecked(0), element_size_); }
begin()60   const_iterator begin() const { return const_iterator(&AtUnchecked(0), element_size_); }
cbegin()61   const_iterator cbegin() const { return const_iterator(&AtUnchecked(0), element_size_); }
end()62   StrideIterator<T> end() { return StrideIterator<T>(&AtUnchecked(size_), element_size_); }
end()63   const_iterator end() const { return const_iterator(&AtUnchecked(size_), element_size_); }
cend()64   const_iterator cend() const { return const_iterator(&AtUnchecked(size_), element_size_); }
rbegin()65   reverse_iterator rbegin() { return reverse_iterator(end()); }
rbegin()66   const_reverse_iterator rbegin() const { return const_reverse_iterator(end()); }
crbegin()67   const_reverse_iterator crbegin() const { return const_reverse_iterator(cend()); }
rend()68   reverse_iterator rend() { return reverse_iterator(begin()); }
rend()69   const_reverse_iterator rend() const { return const_reverse_iterator(begin()); }
crend()70   const_reverse_iterator crend() const { return const_reverse_iterator(cbegin()); }
71 
72   // Size.
size()73   size_type size() const { return size_; }
empty()74   bool empty() const { return size() == 0u; }
75 
76   // Element access. NOTE: Not providing at() and data().
77 
78   reference operator[](size_t index) {
79     DCHECK_LT(index, size_);
80     return AtUnchecked(index);
81   }
82 
83   const_reference operator[](size_t index) const {
84     DCHECK_LT(index, size_);
85     return AtUnchecked(index);
86   }
87 
front()88   reference front() {
89     DCHECK(!empty());
90     return (*this)[0];
91   }
92 
front()93   const_reference front() const {
94     DCHECK(!empty());
95     return (*this)[0];
96   }
97 
back()98   reference back() {
99     DCHECK(!empty());
100     return (*this)[size_ - 1u];
101   }
102 
back()103   const_reference back() const {
104     DCHECK(!empty());
105     return (*this)[size_ - 1u];
106   }
107 
SubArray(size_type pos)108   ArraySlice<T> SubArray(size_type pos) {
109     return SubArray(pos, size() - pos);
110   }
111 
SubArray(size_type pos)112   ArraySlice<const T> SubArray(size_type pos) const {
113     return SubArray(pos, size() - pos);
114   }
115 
SubArray(size_type pos,size_type length)116   ArraySlice<T> SubArray(size_type pos, size_type length) {
117     DCHECK_LE(pos, size());
118     DCHECK_LE(length, size() - pos);
119     return ArraySlice<T>(&AtUnchecked(pos), length, element_size_);
120   }
121 
SubArray(size_type pos,size_type length)122   ArraySlice<const T> SubArray(size_type pos, size_type length) const {
123     DCHECK_LE(pos, size());
124     DCHECK_LE(length, size() - pos);
125     return ArraySlice<const T>(&AtUnchecked(pos), length, element_size_);
126   }
127 
ElementSize()128   size_t ElementSize() const {
129     return element_size_;
130   }
131 
Contains(const T * element)132   bool Contains(const T* element) const {
133     return &AtUnchecked(0) <= element && element < &AtUnchecked(size_);
134   }
135 
136  private:
AtUnchecked(size_t index)137   T& AtUnchecked(size_t index) {
138     return *reinterpret_cast<T*>(reinterpret_cast<uintptr_t>(array_) + index * element_size_);
139   }
140 
AtUnchecked(size_t index)141   const T& AtUnchecked(size_t index) const {
142     return *reinterpret_cast<T*>(reinterpret_cast<uintptr_t>(array_) + index * element_size_);
143   }
144 
145   T* array_;
146   size_t size_;
147   size_t element_size_;
148 };
149 
150 }  // namespace art
151 
152 #endif  // ART_LIBARTBASE_BASE_ARRAY_SLICE_H_
153