text: // A filter block is stored near the end of a Table file.  It contains
  // filters (e.g., bloom filters) for all data blocks in the table combined
  // into a single filter block.
  
  #ifndef STORAGE_LEVELDB_TABLE_FILTER_BLOCK_H_
  #define STORAGE_LEVELDB_TABLE_FILTER_BLOCK_H_
  
  #include <stddef.h>
  #include <stdint.h>
  #include <string>
  #include <vector>
  #include "leveldb/slice.h"
  #include "util/hash.h"
  
  namespace leveldb {
  
  class FilterPolicy;
  
  // A FilterBlockBuilder is used to construct all of the filters for a
  // particular Table.  It generates a single string which is stored as
  // a special block in the Table.
  //
  // The sequence of calls to FilterBlockBuilder must match the regexp:
  //      (StartBlock AddKey*)* Finish
  class FilterBlockBuilder {
   public:
    explicit FilterBlockBuilder(const FilterPolicy*);
  
    void StartBlock(uint64_t block_offset);
    void AddKey(const Slice& key);
    Slice Finish();
  
   private:
    void GenerateFilter();
  
    const FilterPolicy* policy_;
    std::string keys_;              // Flattened key contents
    std::vector<size_t> start_;     // Starting index in keys_ of each key
    std::string result_;            // Filter data computed so far
    std::vector<Slice> tmp_keys_;   // policy_->CreateFilter() argument
    std::vector<uint32_t> filter_offsets_;
  
    // No copying allowed
    FilterBlockBuilder(const FilterBlockBuilder&);
    void operator=(const FilterBlockBuilder&);
  };
  
  class FilterBlockReader {
   public:
   // REQUIRES: "contents" and *policy must stay live while *this is live.
    FilterBlockReader(const FilterPolicy* policy, const Slice& contents);
    bool KeyMayMatch(uint64_t block_offset, const Slice& key);
  
   private:
    const FilterPolicy* policy_;
    const char* data_;    // Pointer to filter data (at block-start)
    const char* offset_;  // Pointer to beginning of offset array (at block-end)
    size_t num_;          // Number of entries in offset array
    size_t base_lg_;      // Encoding parameter (see kFilterBaseLg in .cc file)
  };
  
  }
  
  #endif  // STORAGE_LEVELDB_TABLE_FILTER_BLOCK_H_
  