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_RUNTIME_BASE_ARRAY_SLICE_H_
18 #define ART_RUNTIME_BASE_ARRAY_SLICE_H_
19 
20 #include "length_prefixed_array.h"
21 #include "stride_iterator.h"
22 #include "base/bit_utils.h"
23 #include "base/casts.h"
24 #include "base/iteration_range.h"
25 
26 namespace art {
27 
28 // An ArraySlice is an abstraction over an array or a part of an array of a particular type. It does
29 // bounds checking and can be made from several common array-like structures in Art.
30 template<typename T>
31 class ArraySlice {
32  public:
33   // Create an empty array slice.
ArraySlice()34   ArraySlice() : array_(nullptr), size_(0), element_size_(0) {}
35 
36   // Create an array slice of the first 'length' elements of the array, with each element being
37   // element_size bytes long.
38   ArraySlice(T* array,
39              size_t length,
40              size_t element_size = sizeof(T))
array_(array)41       : array_(array),
42         size_(dchecked_integral_cast<uint32_t>(length)),
43         element_size_(element_size) {
44     DCHECK(array_ != nullptr || length == 0);
45   }
46 
47   // Create an array slice of the elements between start_offset and end_offset of the array with
48   // each element being element_size bytes long. Both start_offset and end_offset are in
49   // element_size units.
50   ArraySlice(T* array,
51              uint32_t start_offset,
52              uint32_t end_offset,
53              size_t element_size = sizeof(T))
array_(nullptr)54       : array_(nullptr),
55         size_(end_offset - start_offset),
56         element_size_(element_size) {
57     DCHECK(array_ != nullptr || size_ == 0);
58     DCHECK_LE(start_offset, end_offset);
59     if (size_ != 0) {
60       uintptr_t offset = start_offset * element_size_;
61       array_ = *reinterpret_cast<T*>(reinterpret_cast<uintptr_t>(array) + offset);
62     }
63   }
64 
65   // Create an array slice of the elements between start_offset and end_offset of the array with
66   // each element being element_size bytes long and having the given alignment. Both start_offset
67   // and end_offset are in element_size units.
68   ArraySlice(LengthPrefixedArray<T>* array,
69              uint32_t start_offset,
70              uint32_t end_offset,
71              size_t element_size = sizeof(T),
72              size_t alignment = alignof(T))
array_(nullptr)73       : array_(nullptr),
74         size_(end_offset - start_offset),
75         element_size_(element_size) {
76     DCHECK(array != nullptr || size_ == 0);
77     if (size_ != 0) {
78       DCHECK_LE(start_offset, end_offset);
79       DCHECK_LE(start_offset, array->size());
80       DCHECK_LE(end_offset, array->size());
81       array_ = &array->At(start_offset, element_size_, alignment);
82     }
83   }
84 
At(size_t index)85   T& At(size_t index) {
86     DCHECK_LT(index, size_);
87     return AtUnchecked(index);
88   }
89 
At(size_t index)90   const T& At(size_t index) const {
91     DCHECK_LT(index, size_);
92     return AtUnchecked(index);
93   }
94 
95   T& operator[](size_t index) {
96     return At(index);
97   }
98 
99   const T& operator[](size_t index) const {
100     return At(index);
101   }
102 
begin()103   StrideIterator<T> begin() {
104     return StrideIterator<T>(&AtUnchecked(0), element_size_);
105   }
106 
begin()107   StrideIterator<const T> begin() const {
108     return StrideIterator<const T>(&AtUnchecked(0), element_size_);
109   }
110 
end()111   StrideIterator<T> end() {
112     return StrideIterator<T>(&AtUnchecked(size_), element_size_);
113   }
114 
end()115   StrideIterator<const T> end() const {
116     return StrideIterator<const T>(&AtUnchecked(size_), element_size_);
117   }
118 
AsRange()119   IterationRange<StrideIterator<T>> AsRange() {
120     return size() != 0 ? MakeIterationRange(begin(), end())
121                        : MakeEmptyIterationRange(StrideIterator<T>(nullptr, 0));
122   }
123 
size()124   size_t size() const {
125     return 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_RUNTIME_BASE_ARRAY_SLICE_H_
153