1 /*
2  * Copyright (C) 2014 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 __BYTE_BUCKET_ARRAY_H
18 #define __BYTE_BUCKET_ARRAY_H
19 
20 #include <algorithm>
21 #include <cstdint>
22 #include <cstring>
23 
24 #include "android-base/logging.h"
25 
26 namespace android {
27 
28 /**
29  * Stores a sparsely populated array. Has a fixed size of 256
30  * (number of entries that a byte can represent).
31  */
32 template <typename T>
33 class ByteBucketArray {
34  public:
ByteBucketArray()35   ByteBucketArray() {
36     memset(buckets_, 0, sizeof(buckets_));
37   }
38 
~ByteBucketArray()39   ~ByteBucketArray() {
40     deleteBuckets();
41   }
42 
clear()43   void clear() {
44     deleteBuckets();
45     memset(buckets_, 0, sizeof(buckets_));
46   }
47 
size()48   inline size_t size() const { return kNumBuckets * kBucketSize; }
49 
get(size_t index)50   inline const T& get(size_t index) const { return (*this)[index]; }
51 
52   const T& operator[](size_t index) const {
53     if (index >= size()) {
54       return default_;
55     }
56 
57     uint8_t bucket_index = static_cast<uint8_t>(index) >> 4;
58     T* bucket = buckets_[bucket_index];
59     if (bucket == nullptr) {
60       return default_;
61     }
62     return bucket[0x0f & static_cast<uint8_t>(index)];
63   }
64 
editItemAt(size_t index)65   T& editItemAt(size_t index) {
66     CHECK(index < size()) << "ByteBucketArray.editItemAt(index=" << index
67                           << ") with size=" << size();
68 
69     uint8_t bucket_index = static_cast<uint8_t>(index) >> 4;
70     T*& bucket = buckets_[bucket_index];
71     if (bucket == nullptr) {
72       bucket = new T[kBucketSize]();
73     }
74     return bucket[0x0f & static_cast<uint8_t>(index)];
75   }
76 
set(size_t index,const T & value)77   bool set(size_t index, const T& value) {
78     if (index >= size()) {
79       return false;
80     }
81 
82     editItemAt(index) = value;
83     return true;
84   }
85 
86   template <class Func>
forEachItem(Func f)87   void forEachItem(Func f) {
88     for (size_t i = 0; i < kNumBuckets; i++) {
89       const auto bucket = buckets_[i];
90       if (bucket != nullptr) {
91         for (size_t j = 0; j < kBucketSize; j++) {
92           f((i << 4) | j, bucket[j]);
93         }
94       }
95     }
96   }
97 
98   template <class Func>
trimBuckets(Func isEmptyFunc)99   void trimBuckets(Func isEmptyFunc) {
100     for (size_t i = 0; i < kNumBuckets; i++) {
101       const auto bucket = buckets_[i];
102       if (bucket != nullptr) {
103         if (std::all_of(bucket, bucket + kBucketSize, isEmptyFunc)) {
104           delete[] bucket;
105           buckets_[i] = nullptr;
106         }
107       }
108     }
109   }
110 
111  private:
112   enum { kNumBuckets = 16, kBucketSize = 16 };
113 
deleteBuckets()114   void deleteBuckets() {
115     for (size_t i = 0; i < kNumBuckets; i++) {
116       if (buckets_[i] != nullptr) {
117         delete[] buckets_[i];
118       }
119     }
120   }
121 
122   T* buckets_[kNumBuckets];
123   static inline const T default_ = {};
124 };
125 
126 }  // namespace android
127 
128 #endif  // __BYTE_BUCKET_ARRAY_H
129