diff --git a/cxxmph/Makefile.am b/cxxmph/Makefile.am
index 0534c68..f99a284 100644
--- a/cxxmph/Makefile.am
+++ b/cxxmph/Makefile.am
@@ -1,5 +1,5 @@
 TESTS = $(check_PROGRAMS)
-check_PROGRAMS = mph_bits_test hollow_iterator_test mph_map_test mph_index_test trigraph_test
+check_PROGRAMS = seeded_hash_test mph_bits_test hollow_iterator_test mph_map_test mph_index_test trigraph_test
 noinst_PROGRAMS = bm_index bm_map
 bin_PROGRAMS = cxxmph
 lib_LTLIBRARIES = libcxxmph.la
@@ -27,9 +27,10 @@ cxxmph_LDADD   = libcxxmph.la
 cxxmph_SOURCES = cxxmph.cc
 
 hollow_iterator_test_SOURCES = hollow_iterator_test.cc
+
 seeded_hash_test_SOURCES = seeded_hash_test.cc
+seeded_hash_test_LDADD   = libcxxmph.la
 
 mph_bits_test_SOURCES = mph_bits_test.cc
 mph_bits_test_LDADD   = libcxxmph.la
-mph_bits_test_LDADD   = libcxxmph.la
 
diff --git a/cxxmph/bm_map.cc b/cxxmph/bm_map.cc
index 0a0b225..1708c06 100644
--- a/cxxmph/bm_map.cc
+++ b/cxxmph/bm_map.cc
@@ -8,6 +8,9 @@ using cxxmph::mph_map;
 using std::string;
 using std::unordered_map;
 
+// Another reference benchmark:
+// http://blog.aggregateknowledge.com/tag/bigmemory/
+
 namespace cxxmph {
 
 template<class MapType, class T>
diff --git a/cxxmph/mph_bits.h b/cxxmph/mph_bits.h
index c9eaabb..a32f31f 100644
--- a/cxxmph/mph_bits.h
+++ b/cxxmph/mph_bits.h
@@ -63,6 +63,23 @@ static uint32_t nextpoweroftwo(uint32_t k) {
   return k+1;
 }
 
+template <int n, int mask = (1 << 7)> struct bitcount {
+enum { value = (n & mask ? 1:0) + bitcount<n, (mask >> 1)>::value };
+};
+template <int n> struct bitcount<n, 0> { enum { value = 0 }; };
+
+template <int size, int index = size>
+class CompileTimeRankTable {
+public:
+CompileTimeRankTable() : current(bitcount<index - 1>::value) { }
+int operator[] (int i) { return *(&current + size - i - 1); }
+private:
+unsigned char current;
+CompileTimeRankTable<index -1> next;
+};
+template <int size> class CompileTimeRankTable<size, 0> { };
+typedef CompileTimeRankTable<256> Ranktable;
+
 // Interesting bit tricks that might end up here:
 // http://graphics.stanford.edu/~seander/bithacks.html#ZeroInWord
 // Fast a % (k*2^t)
diff --git a/cxxmph/mph_bits_test.cc b/cxxmph/mph_bits_test.cc
index c1680e3..0105265 100644
--- a/cxxmph/mph_bits_test.cc
+++ b/cxxmph/mph_bits_test.cc
@@ -4,6 +4,8 @@
 #include "mph_bits.h"
 
 using cxxmph::dynamic_2bitset;
+using cxxmph::Ranktable;
+
 int main(int argc, char** argv) {
   dynamic_2bitset small(256, true);
   for (int i = 0; i < small.size(); ++i) small.set(i, i % 4);
@@ -52,6 +54,12 @@ int main(int argc, char** argv) {
   empty.clear();
   dynamic_2bitset large(1000, true);
   empty.swap(large);
+  
+  Ranktable ranktable;
+  if (ranktable[0] != 0) exit(-1);
+  if (ranktable[1] != 1) exit(-1);
+  if (ranktable[2] != 1) exit(-1);
+  if (ranktable[255] != 8) exit(-1);
 }
   
   
diff --git a/cxxmph/mph_map.h b/cxxmph/mph_map.h
index ceb3109..dc7134e 100644
--- a/cxxmph/mph_map.h
+++ b/cxxmph/mph_map.h
@@ -112,10 +112,11 @@ class mph_map {
    std::vector<value_type> values_;
    std::vector<bool> present_;
    SimpleMPHIndex<Key, typename seeded_hash<HashFcn>::hash_function> index_;
-   // TODO(davi) optimize slack to hold 128 unique bits from hash64 as key
-   typedef unordered_map<Key, uint32_t, HashFcn, EqualKey, Alloc> slack_type;
+   // TODO(davi) optimize slack to use hash from index rather than calculate its own
+   typedef unordered_map<h128, uint32_t, h128::hash32> slack_type;
    slack_type slack_;
    size_type size_;
+   typename seeded_hash<HashFcn>::hash_function hasher128_;
 
    mutable uint64_t fast_;
    mutable uint64_t fast_taken_;
@@ -148,7 +149,9 @@ MPH_MAP_METHOD_DECL(insert_return_type, insert)(const value_type& x) {
   values_.push_back(x);
   present_.push_back(true);
   ++size_;
-  slack_.insert(make_pair(x.first, values_.size() - 1));
+  h128 h = hasher128_.hash128(x.first, 0);
+  if (slack_.find(h) != slack_.end()) should_pack = true;  // unavoidable pack
+  else slack_.insert(std::make_pair(h, values_.size() - 1));
   if (should_pack) pack();
   it = find(x.first);
   slow_ = 0;
@@ -218,7 +221,7 @@ MPH_MAP_METHOD_DECL(const_iterator, slow_find)(const key_type& k, uint32_t perfe
   }
   if (__builtin_expect(!slack_.empty(), 0)) {
      ++very_slow_;
-     auto sit = slack_.find(k);
+     auto sit = slack_.find(hasher128_.hash128(k, 0));
      if (sit != slack_.end()) return make_iterator(values_.begin() + sit->second);
   }
   return end();
@@ -233,7 +236,7 @@ MPH_MAP_METHOD_DECL(iterator, slow_find)(const key_type& k, uint32_t perfect_has
   }
   if (__builtin_expect(!slack_.empty(), 0)) {
      ++very_slow_;
-     auto sit = slack_.find(k);
+     auto sit = slack_.find(hasher128_.hash128(k, 0));
      if (sit != slack_.end()) return make_iterator(values_.begin() + sit->second);
   }
   return end();
diff --git a/cxxmph/seeded_hash.h b/cxxmph/seeded_hash.h
index be0b39e..7332be4 100644
--- a/cxxmph/seeded_hash.h
+++ b/cxxmph/seeded_hash.h
@@ -4,6 +4,7 @@
 #include <stdint.h>  // for uint32_t and friends
 
 #include <cstdlib>
+#include <cstring>
 #include <unordered_map>  // for std::hash
 
 #include "MurmurHash3.h"
@@ -17,13 +18,15 @@ uint64_t fmix ( uint64_t h );
 namespace cxxmph {
 
 struct h128 {
-  uint32_t operator[](uint8_t i) const { return uint32[i]; }
+  const uint32_t& operator[](uint8_t i) const { return uint32[i]; }
   uint32_t& operator[](uint8_t i) { return uint32[i]; }
-  uint64_t* uint64ptr(bool second) { return reinterpret_cast<uint64_t*>(&uint32[static_cast<uint8_t>(second) << 1]); }
-  uint64_t uint64(bool second) const { return *reinterpret_cast<const uint64_t*>(&uint32[static_cast<uint8_t>(second) << 1]); }
-  bool operator==(const h128 rhs) const { return uint64(0) == rhs.uint64(0) && uint64(1) == rhs.uint64(1); }
+  const uint64_t get64(bool second) const { return (static_cast<uint64_t>(uint32[second << 1]) << 32) | uint32[1 + (second << 1)]; }
+  void set64(uint64_t v, bool second) { uint32[second << 1] = v >> 32; uint32[1+(second<<1)] = ((v << 32) >> 32); }
+  bool operator==(const h128 rhs) const { return memcmp(uint32, rhs.uint32, sizeof(uint32)) == 0; }
 
   uint32_t uint32[4];
+
+  struct hash32 { uint32_t operator()(const cxxmph::h128& h) const { return h[3]; } };
 };
 
 template <class HashFcn>
@@ -83,8 +86,8 @@ struct Murmur3Fmix64bitsType {
   template <class Key>
   h128 hash128(const Key& k) const {
     h128 h;
-    *h.uint64ptr(0) = fmix(k);
-    *h.uint64ptr(1) = fmix(h.uint64(0));
+    h.set64(fmix(k), 0);
+    h.set64(fmix(h.get64(0)), 1);
   }
 };
 
@@ -131,8 +134,8 @@ struct seeded_hash_function<Murmur3Fmix64bitsType> {
   template <class Key>
   h128 hash128(const Key& k, uint32_t seed) const {
     h128 h;
-    *h.uint64ptr(0) = fmix(k ^ seed);
-    *h.uint64ptr(1) = fmix(h.uint64(0));
+    h.set64(fmix(k ^ seed), 0);
+    h.set64(fmix(h.get64(0)), 1);
     return h;
   }
 };
diff --git a/cxxmph/seeded_hash_test.cc b/cxxmph/seeded_hash_test.cc
new file mode 100644
index 0000000..e2983b0
--- /dev/null
+++ b/cxxmph/seeded_hash_test.cc
@@ -0,0 +1,59 @@
+#include "seeded_hash.h"
+
+#include <unordered_map>
+#include <string>
+#include <iostream>
+
+using std::cerr;
+using std::endl;
+using std::string;
+using std::unordered_map;
+using namespace cxxmph;
+
+int main(int argc, char** argv) {
+  auto hasher = seeded_hash_function<Murmur3StringPiece>();
+  string key1("0");
+  string key2("1");
+  auto h1 = hasher.hash128(key1, 1);
+  auto h2 = hasher.hash128(key2, 1);
+  if (h1 == h2) {
+    fprintf(stderr, "unexpected murmur collision\n");
+    exit(-1);
+  }
+
+  unordered_map<uint64_t, int, Murmur3Fmix64bitsType> g;
+  for (int i = 0; i < 1000; ++i) g[i] = i;
+  for (int i = 0; i < 1000; ++i) if (g[i] != i) exit(-1);
+
+  auto inthasher = seeded_hash_function<std::hash<uint64_t>>();
+  unordered_map<h128, int, h128::hash32> g2;
+  for (uint64_t i = 0; i < 1000; ++i) {
+    auto h = inthasher.hash128(i, 0);
+    if (g2.find(h) != g2.end()) {
+      std::cerr << "Incorrectly found " << i << std::endl;
+      exit(-1);
+    }
+    if (h128::hash32()(h) != h[3]) {
+      cerr << "Buggy hash method." << endl;
+      exit(-1);
+    }
+    auto h2 = inthasher.hash128(i, 0);
+    if (!(h == h2)) {
+      cerr << "h 64(0) " << h.get64(0) << " h 64(1) " << h.get64(1) << endl;
+      cerr << " h2 64(0) " << h2.get64(0) << " h2 64(1) " << h2.get64(1) << endl;
+      cerr << "Broken equality for h128" << endl;
+      exit(-1);
+    }
+    if (h128::hash32()(h) != h128::hash32()(h2)) {
+      cerr << "Inconsistent hash method." << endl;
+      exit(-1);
+    }
+    g2[h] = i;
+    if (g2.find(h) == g2.end()) {
+      std::cerr << "Incorrectly missed " << i << std::endl;
+      exit(-1);
+    }
+  }
+    
+  for (uint64_t i = 0; i < 1000; ++i) if (g2[inthasher.hash128(i, 0)] != i) exit(-1);
+}