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      1 /*
      2  * Copyright (C) 2017 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_DEX2OAT_LINKER_INDEX_BSS_MAPPING_ENCODER_H_
     18 #define ART_DEX2OAT_LINKER_INDEX_BSS_MAPPING_ENCODER_H_
     19 
     20 #include <android-base/logging.h>
     21 
     22 #include "base/bit_utils.h"
     23 #include "base/bit_vector-inl.h"
     24 #include "index_bss_mapping.h"
     25 
     26 namespace art {
     27 namespace linker {
     28 
     29 // Helper class for encoding compressed IndexBssMapping.
     30 class IndexBssMappingEncoder {
     31  public:
     32   IndexBssMappingEncoder(size_t number_of_indexes, size_t slot_size)
     33       : index_bits_(IndexBssMappingEntry::IndexBits(number_of_indexes)),
     34         slot_size_(slot_size) {
     35     entry_.index_and_mask = static_cast<uint32_t>(-1);
     36     entry_.bss_offset = static_cast<uint32_t>(-1);
     37     DCHECK_NE(number_of_indexes, 0u);
     38   }
     39 
     40   // Try to merge the next index -> bss_offset mapping into the current entry.
     41   // Return true on success, false on failure.
     42   bool TryMerge(uint32_t index, uint32_t bss_offset) {
     43     DCHECK_LE(MinimumBitsToStore(index), index_bits_);
     44     DCHECK_NE(index, entry_.GetIndex(index_bits_));
     45     if (entry_.bss_offset + slot_size_ != bss_offset) {
     46       return false;
     47     }
     48     uint32_t diff = index - entry_.GetIndex(index_bits_);
     49     if (diff > 32u - index_bits_) {
     50       return false;
     51     }
     52     uint32_t mask = entry_.GetMask(index_bits_);
     53     if ((mask & ~(static_cast<uint32_t>(-1) << diff)) != 0u) {
     54       return false;
     55     }
     56     // Insert the bit indicating the index we've just overwritten
     57     // and shift bits indicating indexes before that.
     58     mask = ((mask << index_bits_) >> diff) | (static_cast<uint32_t>(1u) << (32 - diff));
     59     entry_.index_and_mask = mask | index;
     60     entry_.bss_offset = bss_offset;
     61     return true;
     62   }
     63 
     64   void Reset(uint32_t method_index, uint32_t bss_offset) {
     65     DCHECK_LE(MinimumBitsToStore(method_index), index_bits_);
     66     entry_.index_and_mask = method_index;  // Mask bits set to 0.
     67     entry_.bss_offset = bss_offset;
     68   }
     69 
     70   IndexBssMappingEntry GetEntry() {
     71     return entry_;
     72   }
     73 
     74   size_t GetIndexBits() const {
     75     return index_bits_;
     76   }
     77 
     78  private:
     79   const size_t index_bits_;
     80   const size_t slot_size_;
     81   IndexBssMappingEntry entry_;
     82 };
     83 
     84 }  // namespace linker
     85 }  // namespace art
     86 
     87 #endif  // ART_DEX2OAT_LINKER_INDEX_BSS_MAPPING_ENCODER_H_
     88