Example of using KenLM's probing hash map for one's own evil purposes

dumb.cc

// building:                                                                                                                                 
// g++ -I$HOME/prefix/include/ -Iklm -c dumb.cc                                                                                              
// g++ -lz klm/util/file.o klm/util/mmap.o klm/util/exception.o dumb.o -o dumb                                                               

#include <stdint.h>
#include <iostream>
using namespace std;

#include <boost/functional/hash.hpp>

#include "util/probing_hash_table.hh"
#include "util/scoped.hh"
#include "util/file.hh"
#include "util/mmap.hh"

struct Entry {
  unsigned char key;
  typedef unsigned char Key;

  unsigned char GetKey() const {
    return key;
  }

  uint64_t GetValue() const {
    return value;
  }

  uint64_t value;
};

typedef util::ProbingHashTable<Entry, boost::hash<unsigned char> > Table;

int main(int argc, char** argv) {

  char* filename = "x.bin";
  {
    float load_factor = 1.5;
    int num_elements = 10;
    size_t bytes = Table::Size(num_elements, load_factor);
    util::scoped_fd file;
    util::scoped_mmap mem(MapZeroedWrite(filename, bytes, file), bytes);
    Table table(mem.get(), mem.size());

    Entry to_ins;
    to_ins.key = 3;
    to_ins.value = 328920;
    cerr << "Inserting: " << (int) to_ins.key << " " << to_ins.value << endl;
    table.Insert(to_ins);

    cerr << "Closing " << filename << endl;

 }

  {
    cerr << "Opening " << filename << endl;

    util::scoped_fd file(util::OpenReadOrThrow(filename));
    uint64_t size = util::SizeFile(file.get());
    util::scoped_memory mem;
    MapRead(util::POPULATE_OR_READ, file.get(), 0, size, mem);
    Table table(mem.get(), mem.size());

    const Entry *i = NULL;
    table.Find(3, i);
    cerr << "Foudn: " <<  (int) i->key << " " << i->value << endl;
  }

  return 0;
}

See also https://github.com/kpu/kenlm/tree/master/util