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      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 <cstdint>
     21 #include <cstring>
     22 
     23 #include "android-base/logging.h"
     24 
     25 namespace android {
     26 
     27 /**
     28  * Stores a sparsely populated array. Has a fixed size of 256
     29  * (number of entries that a byte can represent).
     30  */
     31 template <typename T>
     32 class ByteBucketArray {
     33  public:
     34   ByteBucketArray() : default_() { memset(buckets_, 0, sizeof(buckets_)); }
     35 
     36   ~ByteBucketArray() {
     37     for (size_t i = 0; i < kNumBuckets; i++) {
     38       if (buckets_[i] != NULL) {
     39         delete[] buckets_[i];
     40       }
     41     }
     42     memset(buckets_, 0, sizeof(buckets_));
     43   }
     44 
     45   inline size_t size() const { return kNumBuckets * kBucketSize; }
     46 
     47   inline const T& get(size_t index) const { return (*this)[index]; }
     48 
     49   const T& operator[](size_t index) const {
     50     if (index >= size()) {
     51       return default_;
     52     }
     53 
     54     uint8_t bucket_index = static_cast<uint8_t>(index) >> 4;
     55     T* bucket = buckets_[bucket_index];
     56     if (bucket == NULL) {
     57       return default_;
     58     }
     59     return bucket[0x0f & static_cast<uint8_t>(index)];
     60   }
     61 
     62   T& editItemAt(size_t index) {
     63     CHECK(index < size()) << "ByteBucketArray.getOrCreate(index=" << index
     64                           << ") with size=" << size();
     65 
     66     uint8_t bucket_index = static_cast<uint8_t>(index) >> 4;
     67     T* bucket = buckets_[bucket_index];
     68     if (bucket == NULL) {
     69       bucket = buckets_[bucket_index] = new T[kBucketSize]();
     70     }
     71     return bucket[0x0f & static_cast<uint8_t>(index)];
     72   }
     73 
     74   bool set(size_t index, const T& value) {
     75     if (index >= size()) {
     76       return false;
     77     }
     78 
     79     editItemAt(index) = value;
     80     return true;
     81   }
     82 
     83  private:
     84   enum { kNumBuckets = 16, kBucketSize = 16 };
     85 
     86   T* buckets_[kNumBuckets];
     87   T default_;
     88 };
     89 
     90 }  // namespace android
     91 
     92 #endif  // __BYTE_BUCKET_ARRAY_H
     93