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turbonss/cxxmph/mphtable.h

159 lines
5.0 KiB
C++

#ifndef __CXXMPH_MPHTABLE_H__
#define __CXXMPH_MPHTABLE_H__
// Minimal perfect hash abstraction implementing the BDZ algorithm
#include <stdint.h>
#include <cassert>
#include <cmath>
#include <unordered_map> // for std::hash
#include <vector>
#include <iostream>
using std::cerr;
using std::endl;
#include "cxxmph_hash.h"
#include "trigraph.h"
namespace cxxmph {
class MPHTable {
public:
MPHTable(double c = 1.23, uint8_t b = 7) :
c_(c), b_(b), m_(0), n_(0), k_(0), r_(0) { }
~MPHTable() {}
template <class SeededHashFcn, class ForwardIterator>
bool Reset(ForwardIterator begin, ForwardIterator end);
template <class SeededHashFcn, class Key> // must agree with Reset
uint32_t index(const Key& x) const;
uint32_t size() const { return m_; }
void clear();
private:
template <class SeededHashFcn, class ForwardIterator>
bool Mapping(ForwardIterator begin, ForwardIterator end,
std::vector<TriGraph::Edge>* edges,
std::vector<uint32_t>* queue);
bool GenerateQueue(TriGraph* graph, std::vector<uint32_t>* queue);
void Assigning(const std::vector<TriGraph::Edge>& edges,
const std::vector<uint32_t>& queue);
void Ranking();
uint32_t Rank(uint32_t vertex) const;
// Algorithm parameters
double c_; // Number of bits per key (? is it right)
uint8_t b_; // Number of bits of the kth index in the ranktable
// Values used during generation
uint32_t m_; // edges count
uint32_t n_; // vertex count
uint32_t k_; // kth index in ranktable, $k = log_2(n=3r)\varepsilon$
// Values used during search
// Partition vertex count, derived from c parameter.
uint32_t r_;
// The array containing the minimal perfect hash function graph.
std::vector<uint8_t> g_;
// The table used for the rank step of the minimal perfect hash function
std::vector<uint32_t> ranktable_;
// The selected hash seed triplet for finding the edges in the minimal
// perfect hash function graph.
uint32_t hash_seed_[3];
static const uint8_t valuemask[];
static void set_2bit_value(std::vector<uint8_t> *d, uint32_t i, uint8_t v) {
(*d)[(i >> 2)] &= (v << ((i & 3) << 1)) | valuemask[i & 3];
}
static uint32_t get_2bit_value(const std::vector<uint8_t>& d, uint32_t i) {
return (d[(i >> 2)] >> ((i & 3) << 1)) & 3;
}
};
// Template method needs to go in the header file.
template <class SeededHashFcn, class ForwardIterator>
bool MPHTable::Reset(ForwardIterator begin, ForwardIterator end) {
m_ = end - begin;
r_ = static_cast<uint32_t>(ceil((c_*m_)/3));
if ((r_ % 2) == 0) r_ += 1;
n_ = 3*r_;
k_ = 1U << b_;
// cerr << "m " << m_ << " n " << n_ << " r " << r_ << endl;
int iterations = 10;
std::vector<TriGraph::Edge> edges;
std::vector<uint32_t> queue;
while (1) {
// cerr << "Iterations missing: " << iterations << endl;
for (int i = 0; i < 3; ++i) hash_seed_[i] = random() % m_;
// for (int i = 0; i < 3; ++i) hash_seed_[i] = random() + i;
if (Mapping<SeededHashFcn>(begin, end, &edges, &queue)) break;
else --iterations;
if (iterations == 0) break;
}
if (iterations == 0) return false;
Assigning(edges, queue);
std::vector<TriGraph::Edge>().swap(edges);
Ranking();
return true;
}
template <class SeededHashFcn, class ForwardIterator>
bool MPHTable::Mapping(
ForwardIterator begin, ForwardIterator end,
std::vector<TriGraph::Edge>* edges, std::vector<uint32_t>* queue) {
TriGraph graph(n_, m_);
for (ForwardIterator it = begin; it != end; ++it) {
uint32_t h[3];
for (int i = 0; i < 3; ++i) h[i] = SeededHashFcn()(*it, hash_seed_[i]);
uint32_t v0 = h[0] % r_;
uint32_t v1 = h[1] % r_ + r_;
uint32_t v2 = h[2] % r_ + (r_ << 1);
// cerr << "Key: " << *it << " edge " << it - begin << " (" << v0 << "," << v1 << "," << v2 << ")" << endl;
graph.AddEdge(TriGraph::Edge(v0, v1, v2));
}
if (GenerateQueue(&graph, queue)) {
graph.ExtractEdgesAndClear(edges);
return true;
}
return false;
}
template <class SeededHashFcn, class Key>
uint32_t MPHTable::index(const Key& key) const {
uint32_t h[3];
for (int i = 0; i < 3; ++i) h[i] = SeededHashFcn()(key, hash_seed_[i]);
h[0] = h[0] % r_;
h[1] = h[1] % r_ + r_;
h[2] = h[2] % r_ + (r_ << 1);
assert(g_.size());
//cerr << "g_.size() " << g_.size() << " h0 >> 2 " << (h[0] >> 2) << endl;
assert((h[0] >> 2) <g_.size());
assert((h[1] >> 2) <g_.size());
assert((h[2] >> 2) <g_.size());
uint32_t vertex = h[(get_2bit_value(g_, h[0]) + get_2bit_value(g_, h[1]) + get_2bit_value(g_, h[2])) % 3];
// cerr << "Search found vertex " << vertex << endl;
return Rank(vertex);
}
template <class Key, class HashFcn = typename cxxmph_hash<std::hash<Key> >::hash_function>
class SimpleMPHTable : public MPHTable {
public:
template <class ForwardIterator>
bool Reset(ForwardIterator begin, ForwardIterator end) {
return MPHTable::Reset<HashFcn>(begin, end);
}
uint32_t index(const Key& key) { return MPHTable::index<HashFcn>(key); }
};
} // namespace cxxmph
#endif // __CXXMPH_MPHTABLE_H__