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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 ART_COMPILER_GC_MAP_BUILDER_H_
     18 #define ART_COMPILER_GC_MAP_BUILDER_H_
     19 
     20 #include <vector>
     21 
     22 #include "gc_map.h"
     23 #include "utils.h"
     24 
     25 namespace art {
     26 
     27 class GcMapBuilder {
     28  public:
     29   GcMapBuilder(std::vector<uint8_t>* table, size_t entries, uint32_t max_native_offset,
     30                size_t references_width)
     31       : entries_(entries), references_width_(entries != 0u ? references_width : 0u),
     32         native_offset_width_(entries != 0 && max_native_offset != 0
     33                              ? sizeof(max_native_offset) - CLZ(max_native_offset) / 8u
     34                              : 0u),
     35         in_use_(entries), table_(table) {
     36     // Resize table and set up header.
     37     table->resize((EntryWidth() * entries) + sizeof(uint32_t));
     38     CHECK_LT(native_offset_width_, 1U << 3);
     39     (*table)[0] = native_offset_width_ & 7;
     40     CHECK_LT(references_width_, 1U << 13);
     41     (*table)[0] |= (references_width_ << 3) & 0xFF;
     42     (*table)[1] = (references_width_ >> 5) & 0xFF;
     43     CHECK_LT(entries, 1U << 16);
     44     (*table)[2] = entries & 0xFF;
     45     (*table)[3] = (entries >> 8) & 0xFF;
     46   }
     47 
     48   void AddEntry(uint32_t native_offset, const uint8_t* references) {
     49     size_t table_index = TableIndex(native_offset);
     50     while (in_use_[table_index]) {
     51       table_index = (table_index + 1) % entries_;
     52     }
     53     in_use_[table_index] = true;
     54     SetCodeOffset(table_index, native_offset);
     55     DCHECK_EQ(native_offset, GetCodeOffset(table_index));
     56     SetReferences(table_index, references);
     57   }
     58 
     59  private:
     60   size_t TableIndex(uint32_t native_offset) {
     61     return NativePcOffsetToReferenceMap::Hash(native_offset) % entries_;
     62   }
     63 
     64   uint32_t GetCodeOffset(size_t table_index) {
     65     uint32_t native_offset = 0;
     66     size_t table_offset = (table_index * EntryWidth()) + sizeof(uint32_t);
     67     for (size_t i = 0; i < native_offset_width_; i++) {
     68       native_offset |= (*table_)[table_offset + i] << (i * 8);
     69     }
     70     return native_offset;
     71   }
     72 
     73   void SetCodeOffset(size_t table_index, uint32_t native_offset) {
     74     size_t table_offset = (table_index * EntryWidth()) + sizeof(uint32_t);
     75     for (size_t i = 0; i < native_offset_width_; i++) {
     76       (*table_)[table_offset + i] = (native_offset >> (i * 8)) & 0xFF;
     77     }
     78   }
     79 
     80   void SetReferences(size_t table_index, const uint8_t* references) {
     81     size_t table_offset = (table_index * EntryWidth()) + sizeof(uint32_t);
     82     memcpy(&(*table_)[table_offset + native_offset_width_], references, references_width_);
     83   }
     84 
     85   size_t EntryWidth() const {
     86     return native_offset_width_ + references_width_;
     87   }
     88 
     89   // Number of entries in the table.
     90   const size_t entries_;
     91   // Number of bytes used to encode the reference bitmap.
     92   const size_t references_width_;
     93   // Number of bytes used to encode a native offset.
     94   const size_t native_offset_width_;
     95   // Entries that are in use.
     96   std::vector<bool> in_use_;
     97   // The table we're building.
     98   std::vector<uint8_t>* const table_;
     99 };
    100 
    101 }  // namespace art
    102 
    103 #endif  // ART_COMPILER_GC_MAP_BUILDER_H_
    104