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1 /*
2  * Copyright (C) 2013 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_BOUNDED_FIFO_H_
18 #define ART_RUNTIME_BASE_BOUNDED_FIFO_H_
19 
20 namespace art {
21 
22 // A bounded fifo is a fifo which has a bounded size. The power of two version uses a bit mask to
23 // avoid needing to deal with wrapping integers around or using a modulo operation.
24 template <typename T, const size_t MaxSize>
25 class BoundedFifoPowerOfTwo {
26  public:
BoundedFifoPowerOfTwo()27   BoundedFifoPowerOfTwo() {
28     // TODO: Do this with a compile time check.
29     CHECK(IsPowerOfTwo(MaxSize));
30     clear();
31   }
32 
clear()33   void clear() {
34     back_index_ = 0;
35     size_ = 0;
36   }
37 
empty()38   bool empty() const {
39     return size() == 0;
40   }
41 
size()42   size_t size() const {
43     return size_;
44   }
45 
push_back(const T & value)46   void push_back(const T& value) {
47     ++size_;
48     DCHECK_LE(size_, MaxSize);
49     // Relies on integer overflow behavior.
50     data_[back_index_++ & mask_] = value;
51   }
52 
front()53   const T& front() const {
54     DCHECK_GT(size_, 0U);
55     return data_[(back_index_ - size_) & mask_];
56   }
57 
pop_front()58   void pop_front() {
59     DCHECK_GT(size_, 0U);
60     --size_;
61   }
62 
63  private:
64   static const size_t mask_ = MaxSize - 1;
65   size_t back_index_, size_;
66   T data_[MaxSize];
67 };
68 
69 }  // namespace art
70 
71 #endif  // ART_RUNTIME_BASE_BOUNDED_FIFO_H_
72