Finally beat STL. Trying improvement around cuckoo hashing idea.

cxxmph/bm_map.cc

@@ -49,6 +49,7 @@ class BM_SearchUrls : public SearchUrlsBenchmark {
       mymap_[*it] = *it;
     }
     mymap_.rehash(mymap_.bucket_count());
+    fprintf(stderr, "Occupation: %f\n", static_cast<float>(mymap_.size())/mymap_.bucket_count());
     return true;
   }
   MapType mymap_;
@@ -57,7 +58,7 @@ class BM_SearchUrls : public SearchUrlsBenchmark {
 template <class MapType>
 class BM_SearchUint64 : public SearchUint64Benchmark {
  public:
-  BM_SearchUint64() : SearchUint64Benchmark(10000, 10*1000*1000) { }
+  BM_SearchUint64() : SearchUint64Benchmark(100000, 10*1000*1000) { }
   virtual bool SetUp() {
     if (!SearchUint64Benchmark::SetUp()) return false;
     for (int i = 0; i < values_.size(); ++i) {
@@ -88,15 +89,13 @@ using namespace cxxmph;
 
 int main(int argc, char** argv) {
   srandom(4);
-  /*
   Benchmark::Register(new BM_CreateUrls<mph_map<StringPiece, StringPiece>>("URLS100k"));
   Benchmark::Register(new BM_CreateUrls<unordered_map<StringPiece, StringPiece>>("URLS100k"));
   Benchmark::Register(new BM_SearchUrls<mph_map<StringPiece, StringPiece>>("URLS100k", 10*1000 * 1000, 0));
   Benchmark::Register(new BM_SearchUrls<unordered_map<StringPiece, StringPiece, Murmur3StringPiece>>("URLS100k", 10*1000 * 1000, 0));
   Benchmark::Register(new BM_SearchUrls<mph_map<StringPiece, StringPiece>>("URLS100k", 10*1000 * 1000, 0.9));
   Benchmark::Register(new BM_SearchUrls<unordered_map<StringPiece, StringPiece, Murmur3StringPiece>>("URLS100k", 10*1000 * 1000, 0.9));
-  */
-  Benchmark::Register(new BM_SearchUint64<unordered_map<uint64_t, uint64_t>>);
   Benchmark::Register(new BM_SearchUint64<mph_map<uint64_t, uint64_t>>);
+  Benchmark::Register(new BM_SearchUint64<unordered_map<uint64_t, uint64_t>>);
   Benchmark::RunAll();
 }

cxxmph/mph_index.h

@@ -25,6 +25,7 @@
 #include <stdint.h>
 
 #include <cassert>
+#include <climits>
 #include <cmath>
 #include <unordered_map>  // for std::hash
 #include <vector>
@@ -63,6 +64,12 @@ class MPHIndex {
   template <class SeededHashFcn, class Key>  // must agree with Reset
   uint32_t minimal_perfect_hash(const Key& x) const;
 
+  // Crazy functions. Ignore.
+  template <class SeededHashFcn, class Key>  // must agree with Reset
+  uint32_t cuckoo_hash(const Key& x, const uint32_t* h, uint8_t nest) const;
+  template <class SeededHashFcn, class Key>  // must agree with Reset
+  void hash_vector(const Key& x, uint32_t* h) const;
+
   // Serialization for mmap usage - not tested well, ping me if you care. 
   // Serialized tables are not guaranteed to work across versions or different
   // endianness (although they could easily be made to be).
@@ -94,6 +101,8 @@ class MPHIndex {
 
   // Partition vertex count, derived from c parameter.
   uint32_t r_;
+  uint32_t nest_displacement_[3];  // derived from r_
+
   // The array containing the minimal perfect hash function graph. Do not use
   // c++ vector to make mmap based backing easier.
   const uint8_t* g_;
@@ -118,6 +127,16 @@ class MPHIndex {
   
 };
 
+template <class T>
+T nexthigher(T k) {
+        if (k == 0)
+                return 1;
+        k--;
+        for (int i=1; i<sizeof(T)*CHAR_BIT; i<<=1)
+                k = k | k >> i;
+        return k+1;
+}
+
 // Template method needs to go in the header file.
 template <class SeededHashFcn, class ForwardIterator>
 bool MPHIndex::Reset(
@@ -129,6 +148,13 @@ bool MPHIndex::Reset(
   m_ = size;
   r_ = static_cast<uint32_t>(ceil((c_*m_)/3));
   if ((r_ % 2) == 0) r_ += 1;
+  nest_displacement_[0] = 0;
+  nest_displacement_[1] = r_;
+  nest_displacement_[2] = (r_ << 1);
+  // This can be used to speed mods, but increases occupation too much. 
+  // Needs to try http://gmplib.org/manual/Integer-Exponentiation.html instead
+  // r_ = nexthigher(r_);
+
   n_ = 3*r_;
   k_ = 1U << b_;
 
@@ -174,15 +200,24 @@ bool MPHIndex::Mapping(
   return false;
 }
 
+template <class SeededHashFcn, class Key>
+uint32_t MPHIndex::cuckoo_hash(const Key& key, const uint32_t* h, uint8_t nest) const {
+  return (h[nest] %  r_) + nest_displacement_[nest];
+}
+
+template <class SeededHashFcn, class Key>
+void MPHIndex::hash_vector(const Key& key, uint32_t* h) const {
+  SeededHashFcn().hash64(key, hash_seed_[0], reinterpret_cast<uint32_t*>(&h));
+}
+
 template <class SeededHashFcn, class Key>
 uint32_t MPHIndex::perfect_hash(const Key& key) const {
   uint32_t h[4];
   SeededHashFcn().hash64(key, hash_seed_[0], reinterpret_cast<uint32_t*>(&h));
   // for (int i = 0; i < 3; ++i) h[i] = SeededHashFcn()(key, hash_seed_[i]);
-  assert(r_);
+  h[0] = (h[0] % r_) + nest_displacement_[0];
-  h[0] = h[0] % r_;
+  h[1] = (h[1] % r_) + nest_displacement_[1];
-  h[1] = h[1] % r_ + r_;
+  h[2] = (h[2] % r_) + nest_displacement_[2];
-  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_);

cxxmph/mph_map.h

@@ -73,7 +73,7 @@ class mph_map {
   data_type& operator[](const key_type &k);
   const data_type& operator[](const key_type &k) const;
 
-  size_type bucket_count() const { return index_.size() + slack_.bucket_count(); }
+  size_type bucket_count() const { return index_.perfect_hash_size() + slack_.bucket_count(); }
   void rehash(size_type nbuckets /*ignored*/); 
 
  protected:  // mimicking STL implementation
@@ -100,9 +100,17 @@ class mph_map {
      return hollow_const_iterator<std::vector<value_type>>(&values_, &present_, it);
    }
 
+   static void set_2bit_value(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 uint8_t* d, uint32_t i) {
+     return (d[(i >> 2)] >> (((i & 3) << 1)) & 3);
+   }
+
    void pack();
    std::vector<value_type> values_;
    std::vector<bool> present_;
+   const uint8_t* nests_;
    SimpleMPHIndex<Key, typename seeded_hash<HashFcn>::hash_function> index_;
    // TODO(davi) optimize slack to no hold a copy of the key
    typedef unordered_map<Key, uint32_t, HashFcn, EqualKey, Alloc> slack_type;
@@ -187,28 +195,48 @@ MPH_MAP_METHOD_DECL(void_type, erase)(const key_type& k) {
 }
 
 MPH_MAP_METHOD_DECL(const_iterator, find)(const key_type& k) const {
-  if (__builtin_expect(!slack_.empty(), 0)) {
+  uint32_t h[4];
-     auto it = slack_.find(k);
+  auto nest = nests_[index_.hash_vector(k, reinterpret_cast<uint32_t*>(&h))];
-     if (it != slack_.end()) return make_iterator(values_.begin() + it->second);
+  if (nest != kNestCollision) {
+    auto vit = values_.begin() + h[nest];
+    if (equal_(k, vit->first)) return make_iterator(vit);
   }
-  if (__builtin_expect(index_.size() == 0, 0)) return end();
+  return slow_find(k);
+}
+
+MPH_MAP_METHOD_DECL(const_iterator, slow_find)(const key_type& k) const {
   auto id = index_.perfect_hash(k);
   if (!present_[id]) return end();
-  auto it = make_iterator(values_.begin() + id);
+  auto vit = values_.begin() + id;
-  if (__builtin_expect(equal_(k, it->first), 1)) return it;
+  if (equal_(k, vit->first)) return make_iterator(vit);
+
+  if (__builtin_expect(!slack_.empty(), 0)) {
+     auto sit = slack_.find(k);
+     if (it != slack_.end()) return make_iterator(values_.begin() + sit->second);
+  }
   return end();
 }
 
 MPH_MAP_METHOD_DECL(iterator, find)(const key_type& k) {
-  if (__builtin_expect(!slack_.empty(), 0)) {
+  uint32_t h[4];
-     auto it = slack_.find(k);
+  auto nest = nests_[index_.hash_vector(k, reinterpret_cast<uint32_t*>(&h))];
-     if (it != slack_.end()) return make_iterator(values_.begin() + it->second);
+  if (nest != kNestCollision) {
+    auto vit = values_.begin() + h[nest];
+    if (equal_(k, vit->first)) return make_iterator(vit);
   }
-  if (__builtin_expect(index_.size() == 0, 0)) return end();
+  return slow_find(k);
+}
+
+MPH_MAP_METHOD_DECL(iterator, slow_find)(const key_type& k) {
   auto id = index_.perfect_hash(k);
   if (!present_[id]) return end();
-  auto it = make_iterator(values_.begin() + id);
+  auto vit = values_.begin() + id;
-  if (__builtin_expect(equal_(k, it->first), 1)) return it;
+  if (equal_(k, vit->first)) return make_iterator(vit);
+
+  if (__builtin_expect(!slack_.empty(), 0)) {
+     auto sit = slack_.find(k);
+     if (it != slack_.end()) return make_iterator(values_.begin() + sit->second);
+  }
   return end();
 }
 

cxxmph/seeded_hash.h

@@ -65,9 +65,8 @@ struct Murmur3Fmix64bitsType {
   }
   template <class Key>
   void hash64(const Key& k, uint32_t* out) const {
-    uint64_t h = fmix(*reinterpret_cast<uint64_t*>(&k));
+    *reinterpret_cast<uint64_t*>(out) = fmix(k);
-    *reinterpret_cast<uint64_t*>(out) = h;
+    *(out + 2) = fmix(*out);
-    *reinterpret_cast<uint64_t*>(out + 2) = h;
   }
 };
 
@@ -145,9 +144,9 @@ template <> struct seeded_hash<std::hash<long> >
 template <> struct seeded_hash<std::hash<unsigned long> >
 { typedef seeded_hash_function<Murmur3> hash_function; };
 template <> struct seeded_hash<std::hash<long long> >
-{ typedef seeded_hash_function<Murmur3Fmix64bitsType> hash_function; };
+{ typedef seeded_hash_function<Murmur3> hash_function; };
 template <> struct seeded_hash<std::hash<unsigned long long> >
-{ typedef seeded_hash_function<Murmur3Fmix64bitsType> hash_function; };
+{ typedef seeded_hash_function<Murmur3> hash_function; };
 
 }  // namespace cxxmph