diff --git a/similarity_search/include/distcomp.h b/similarity_search/include/distcomp.h
index 8fe78bb..0202206 100644
--- a/similarity_search/include/distcomp.h
+++ b/similarity_search/include/distcomp.h
@@ -198,18 +198,18 @@ template <typename T> T LPGenericDistanceOptim(const T* x, const T* y, const int
  * estimators for image classification”. In: Computer Vision and Pattern Recognition (CVPR), 2012 IEEE
  * Conference on, pages 2989–2996
  */
-template <typename T> T alphaBetaDivergence(const T *x, const T *y, const int length, float alpha, float beta);
+template <typename T> T alphaBetaDivergenceSlow(const T *x, const T *y, const int length, float alpha,float beta);
 template <typename T> T alphaBetaDivergenceFast(const T *x, const T *y, const int length, float alpha, float beta);
 
 // A proxy function for alpha-beta divergence that may be used during indexing
-template <typename T> T alphaBetaDivergenceProxy(const T *x, const T *y, const int length, float alpha, float beta);
+template <typename T> T alphaBetaDivergenceSlowProxy(const T *x, const T *y, const int length, float alpha, float beta);
 template <typename T> T alphaBetaDivergenceFastProxy(const T *x, const T *y, const int length, float alpha, float beta);
 /*
  * Renyi divergence.
  * Rényi, Alfréd (1961). "On measures of information and entropy". 
  * Proceedings of the fourth Berkeley Symposium on Mathematics, Statistics and Probability 1960. pp. 547–561. 
  */
-template <typename T> T renyiDivergence(const T *x, const T *y, const int length, float alpha);
+template <typename T> T renyiDivergenceSlow(const T *x, const T *y, const int length, float alpha);
 template <typename T> T renyiDivergenceFast(const T *x, const T *y, const int length, float alpha);
 
 
diff --git a/similarity_search/include/factory/init_spaces.h b/similarity_search/include/factory/init_spaces.h
index 2f9f445..34b676f 100644
--- a/similarity_search/include/factory/init_spaces.h
+++ b/similarity_search/include/factory/init_spaces.h
@@ -138,8 +138,10 @@ inline void initSpaces() {
   REGISTER_SPACE_CREATOR(double, SPACE_SQFD_GAUSSIAN_FUNC, CreateSqfdGaussianFunc)
 #endif
 
-  REGISTER_SPACE_CREATOR(float,  SPACE_AB_DIVERG,  CreateAlphaBetaDiverg)
-  REGISTER_SPACE_CREATOR(double, SPACE_AB_DIVERG,  CreateAlphaBetaDiverg)
+  REGISTER_SPACE_CREATOR(float,  SPACE_AB_DIVERG_SLOW,  CreateAlphaBetaDivergSlow)
+  REGISTER_SPACE_CREATOR(double, SPACE_AB_DIVERG_SLOW,  CreateAlphaBetaDivergSlow)
+  REGISTER_SPACE_CREATOR(float,  SPACE_AB_DIVERG_FAST,  CreateAlphaBetaDivergFast)
+  REGISTER_SPACE_CREATOR(double, SPACE_AB_DIVERG_FAST,  CreateAlphaBetaDivergFast)
 
   REGISTER_SPACE_CREATOR(float,  SPACE_RENYI_DIVERG_SLOW,  CreateRenyiDivergSlow)
   REGISTER_SPACE_CREATOR(double, SPACE_RENYI_DIVERG_SLOW,  CreateRenyiDivergSlow)
diff --git a/similarity_search/include/factory/space/space_ab_diverg.h b/similarity_search/include/factory/space/space_ab_diverg.h
index db40faa..4f77a9a 100644
--- a/similarity_search/include/factory/space/space_ab_diverg.h
+++ b/similarity_search/include/factory/space/space_ab_diverg.h
@@ -22,7 +22,7 @@
 namespace similarity {
 
 template <typename dist_t>
-Space<dist_t>* CreateAlphaBetaDiverg(const AnyParams& AllParams) {
+Space<dist_t>* CreateAlphaBetaDivergSlow(const AnyParams& AllParams) {
   AnyParamManager pmgr(AllParams);
 
   float alpha = 1.0, beta = 1.0;
@@ -30,7 +30,19 @@ Space<dist_t>* CreateAlphaBetaDiverg(const AnyParams& AllParams) {
   pmgr.GetParamOptional("alpha",  alpha, alpha);
   pmgr.GetParamOptional("beta",   beta,  beta);
 
-  return new SpaceAlphaBetaDiverg<dist_t>(alpha, beta);
+  return new SpaceAlphaBetaDivergSlow<dist_t>(alpha, beta);
+}
+
+template <typename dist_t>
+Space<dist_t>* CreateAlphaBetaDivergFast(const AnyParams& AllParams) {
+  AnyParamManager pmgr(AllParams);
+
+  float alpha = 1.0, beta = 1.0;
+
+  pmgr.GetParamOptional("alpha",  alpha, alpha);
+  pmgr.GetParamOptional("beta",   beta,  beta);
+
+  return new SpaceAlphaBetaDivergFast<dist_t>(alpha, beta);
 }
 
 /*
diff --git a/similarity_search/include/space/space_ab_diverg.h b/similarity_search/include/space/space_ab_diverg.h
index 1a64416..f76c4c6 100644
--- a/similarity_search/include/space/space_ab_diverg.h
+++ b/similarity_search/include/space/space_ab_diverg.h
@@ -30,7 +30,8 @@
 #include "space_vector.h"
 #include "distcomp.h"
 
-#define SPACE_AB_DIVERG     "ab_diverg"
+#define SPACE_AB_DIVERG_SLOW     "abdiv_slow"
+#define SPACE_AB_DIVERG_FAST     "abdiv_fast"
 
 namespace similarity {
 
@@ -45,17 +46,32 @@ namespace similarity {
  */
 
 template <typename dist_t>
-class SpaceAlphaBetaDiverg : public VectorSpaceSimpleStorage<dist_t> {
+class SpaceAlphaBetaDivergSlow : public VectorSpaceSimpleStorage<dist_t> {
  public:
-  explicit SpaceAlphaBetaDiverg(float alpha, float beta) : alpha_(alpha), beta_(beta) {}
-  virtual ~SpaceAlphaBetaDiverg() {}
+  explicit SpaceAlphaBetaDivergSlow(float alpha, float beta) : alpha_(alpha), beta_(beta) {}
+  virtual ~SpaceAlphaBetaDivergSlow() {}
 
   virtual std::string StrDesc() const override;
  protected:
   virtual dist_t HiddenDistance(const Object* obj1, const Object* obj2) const override;
   virtual dist_t ProxyDistance(const Object* obj1, const Object* obj2) const override;
  private:
-  DISABLE_COPY_AND_ASSIGN(SpaceAlphaBetaDiverg);
+  DISABLE_COPY_AND_ASSIGN(SpaceAlphaBetaDivergSlow);
+  float alpha_, beta_;
+};
+
+template <typename dist_t>
+class SpaceAlphaBetaDivergFast : public VectorSpaceSimpleStorage<dist_t> {
+ public:
+  explicit SpaceAlphaBetaDivergFast(float alpha, float beta) : alpha_(alpha), beta_(beta) {}
+  virtual ~SpaceAlphaBetaDivergFast() {}
+
+  virtual std::string StrDesc() const override;
+ protected:
+  virtual dist_t HiddenDistance(const Object* obj1, const Object* obj2) const override;
+  virtual dist_t ProxyDistance(const Object* obj1, const Object* obj2) const override;
+ private:
+  DISABLE_COPY_AND_ASSIGN(SpaceAlphaBetaDivergFast);
   float alpha_, beta_;
 };
 
diff --git a/similarity_search/src/distcomp_diverg.cc b/similarity_search/src/distcomp_diverg.cc
index a8320ff..82b56b0 100644
--- a/similarity_search/src/distcomp_diverg.cc
+++ b/similarity_search/src/distcomp_diverg.cc
@@ -28,7 +28,9 @@ namespace similarity {
 
 using namespace std;
 
-template <typename T> T alphaBetaDivergence(const T *x, const T *y, const int length, float alpha, float beta) {
+template <typename T> T alphaBetaDivergenceSlow(const T *x, const T *y,
+                                                const int length, float alpha,
+                                                float beta) {
   T res = 0;
   float alphaPlus1 = alpha + 1;
   for (int i = 0; i < length; ++i) {
@@ -37,8 +39,8 @@ template <typename T> T alphaBetaDivergence(const T *x, const T *y, const int le
   return res;
 }
 
-template  float alphaBetaDivergence(const float* x, const float* y, const int length, float alpha, float beta);
-template  double alphaBetaDivergence(const double* x, const double* y, const int length, float alpha, float beta);
+template  float alphaBetaDivergenceSlow(const float* x, const float* y, const int length, float alpha, float beta);
+template  double alphaBetaDivergenceSlow(const double* x, const double* y, const int length, float alpha, float beta);
 
 template <typename T> T alphaBetaDivergenceFast(const T *x, const T *y, const int length, float alpha, float beta) {
   T res = 0;
@@ -53,7 +55,9 @@ template <typename T> T alphaBetaDivergenceFast(const T *x, const T *y, const in
 template  float alphaBetaDivergenceFast(const float* x, const float* y, const int length, float alpha, float beta);
 template  double alphaBetaDivergenceFast(const double* x, const double* y, const int length, float alpha, float beta);
 
-template <typename T> T alphaBetaDivergenceProxy(const T *x, const T *y, const int length, float alpha, float beta) {
+template <typename T> T alphaBetaDivergenceSlowProxy(const T *x, const T *y,
+                                                     const int length,
+                                                     float alpha, float beta) {
   T res = 0;
   float alphaPlus1 = alpha + 1;
   for (int i = 0; i < length; ++i) {
@@ -63,8 +67,8 @@ template <typename T> T alphaBetaDivergenceProxy(const T *x, const T *y, const i
   return res;
 }
 
-template  float alphaBetaDivergenceProxy(const float* x, const float* y, const int length, float alpha, float beta);
-template  double alphaBetaDivergenceProxy(const double* x, const double* y, const int length, float alpha, float beta);
+template  float alphaBetaDivergenceSlowProxy(const float* x, const float* y, const int length, float alpha, float beta);
+template  double alphaBetaDivergenceSlowProxy(const double* x, const double* y, const int length, float alpha, float beta);
 
 template <typename T> T alphaBetaDivergenceFastProxy(const T *x, const T *y, const int length, float alpha, float beta) {
   PowerProxyObject<T> powalphaPlus1(alpha + 1), powBeta(beta);
@@ -80,7 +84,8 @@ template <typename T> T alphaBetaDivergenceFastProxy(const T *x, const T *y, con
 template  float alphaBetaDivergenceFastProxy(const float* x, const float* y, const int length, float alpha, float beta);
 template  double alphaBetaDivergenceFastProxy(const double* x, const double* y, const int length, float alpha, float beta);
 
-template <typename T> T renyiDivergence(const T *x, const T *y, const int length, float alpha) {
+template <typename T> T renyiDivergenceSlow(const T *x, const T *y,
+                                            const int length, float alpha) {
   T sum = 0;
   T eps = -1e-6;
   float t = alpha-1; 
@@ -93,8 +98,8 @@ template <typename T> T renyiDivergence(const T *x, const T *y, const int length
   return max<T>(0, res);
 }
 
-template  float renyiDivergence(const float* x, const float* y, const int length, float alpha);
-template  double renyiDivergence(const double* x, const double* y, const int length, float alpha);
+template  float renyiDivergenceSlow(const float* x, const float* y, const int length, float alpha);
+template  double renyiDivergenceSlow(const double* x, const double* y, const int length, float alpha);
 
 template <typename T> T renyiDivergenceFast(const T *x, const T *y, const int length, float alpha) {
   float t = alpha-1; 
diff --git a/similarity_search/src/space/space_ab_diverg.cc b/similarity_search/src/space/space_ab_diverg.cc
index 82984f6..a50ec1d 100644
--- a/similarity_search/src/space/space_ab_diverg.cc
+++ b/similarity_search/src/space/space_ab_diverg.cc
@@ -26,35 +26,67 @@
 namespace similarity {
 
 template <typename dist_t>
-dist_t SpaceAlphaBetaDiverg<dist_t>::HiddenDistance(const Object* obj1, const Object* obj2) const {
+dist_t SpaceAlphaBetaDivergSlow<dist_t>::HiddenDistance(const Object* obj1, const Object* obj2) const {
   CHECK(obj1->datalength() > 0);
   CHECK(obj1->datalength() == obj2->datalength());
   const dist_t* x = reinterpret_cast<const dist_t*>(obj1->data());
   const dist_t* y = reinterpret_cast<const dist_t*>(obj2->data());
   const size_t length = obj1->datalength() / sizeof(dist_t);
 
-  return alphaBetaDivergence(x, y, length, alpha_, beta_);
+  return alphaBetaDivergenceSlow(x, y, length, alpha_, beta_);
 }
 
 template <typename dist_t>
-dist_t SpaceAlphaBetaDiverg<dist_t>::ProxyDistance(const Object* obj1, const Object* obj2) const {
+dist_t SpaceAlphaBetaDivergSlow<dist_t>::ProxyDistance(const Object* obj1, const Object* obj2) const {
   CHECK(obj1->datalength() > 0);
   CHECK(obj1->datalength() == obj2->datalength());
   const dist_t* x = reinterpret_cast<const dist_t*>(obj1->data());
   const dist_t* y = reinterpret_cast<const dist_t*>(obj2->data());
   const size_t length = obj1->datalength() / sizeof(dist_t);
 
-  return alphaBetaDivergenceProxy(x, y, length, alpha_, beta_);
+  return alphaBetaDivergenceSlowProxy(x, y, length, alpha_, beta_);
 }
 
 template <typename dist_t>
-std::string SpaceAlphaBetaDiverg<dist_t>::StrDesc() const {
+std::string SpaceAlphaBetaDivergSlow<dist_t>::StrDesc() const {
   std::stringstream stream;
-  stream << SPACE_AB_DIVERG << ":alpha=" << alpha_ << ",beta=" << beta_;
+  stream << SPACE_AB_DIVERG_SLOW << ":alpha=" << alpha_ << ",beta=" << beta_;
   return stream.str();
 }
 
-template class SpaceAlphaBetaDiverg<float>;
-template class SpaceAlphaBetaDiverg<double>;
+template class SpaceAlphaBetaDivergSlow<float>;
+template class SpaceAlphaBetaDivergSlow<double>;
+
+template <typename dist_t>
+dist_t SpaceAlphaBetaDivergFast<dist_t>::HiddenDistance(const Object* obj1, const Object* obj2) const {
+  CHECK(obj1->datalength() > 0);
+  CHECK(obj1->datalength() == obj2->datalength());
+  const dist_t* x = reinterpret_cast<const dist_t*>(obj1->data());
+  const dist_t* y = reinterpret_cast<const dist_t*>(obj2->data());
+  const size_t length = obj1->datalength() / sizeof(dist_t);
+
+  return alphaBetaDivergenceFast(x, y, length, alpha_, beta_);
+}
+
+template <typename dist_t>
+dist_t SpaceAlphaBetaDivergFast<dist_t>::ProxyDistance(const Object* obj1, const Object* obj2) const {
+  CHECK(obj1->datalength() > 0);
+  CHECK(obj1->datalength() == obj2->datalength());
+  const dist_t* x = reinterpret_cast<const dist_t*>(obj1->data());
+  const dist_t* y = reinterpret_cast<const dist_t*>(obj2->data());
+  const size_t length = obj1->datalength() / sizeof(dist_t);
+
+  return alphaBetaDivergenceFastProxy(x, y, length, alpha_, beta_);
+}
+
+template <typename dist_t>
+std::string SpaceAlphaBetaDivergFast<dist_t>::StrDesc() const {
+  std::stringstream stream;
+  stream << SPACE_AB_DIVERG_FAST << ":alpha=" << alpha_ << ",beta=" << beta_;
+  return stream.str();
+}
+
+template class SpaceAlphaBetaDivergFast<float>;
+template class SpaceAlphaBetaDivergFast<double>;
 
 }  // namespace similarity
diff --git a/similarity_search/src/space/space_renyi_diverg.cc b/similarity_search/src/space/space_renyi_diverg.cc
index 32e2067..722009d 100644
--- a/similarity_search/src/space/space_renyi_diverg.cc
+++ b/similarity_search/src/space/space_renyi_diverg.cc
@@ -33,7 +33,7 @@ dist_t SpaceRenyiDivergSlow<dist_t>::HiddenDistance(const Object* obj1, const Ob
   const dist_t* y = reinterpret_cast<const dist_t*>(obj2->data());
   const size_t length = obj1->datalength() / sizeof(dist_t);
 
-  return renyiDivergence(x, y, length, alpha_);
+  return renyiDivergenceSlow(x, y, length, alpha_);
 }
 
 template <typename dist_t>
diff --git a/similarity_search/test/test_distfunc.cc b/similarity_search/test/test_distfunc.cc
index 6ddde93..ef56c13 100644
--- a/similarity_search/test/test_distfunc.cc
+++ b/similarity_search/test/test_distfunc.cc
@@ -575,7 +575,7 @@ bool TestRenyiDivAgree(size_t N, size_t dim, size_t Rep, T alpha) {
             Normalize(pVect1, dim);
             Normalize(pVect2, dim);
 
-            T val0 = renyiDivergence(pVect1, pVect2, dim, alpha);
+            T val0 = renyiDivergenceSlow(pVect1, pVect2, dim, alpha);
             T val1 = renyiDivergenceFast(pVect1, pVect2, dim, alpha);
 
             bool bug = false;
@@ -605,6 +605,53 @@ bool TestRenyiDivAgree(size_t N, size_t dim, size_t Rep, T alpha) {
     return true;
 }
 
+template <class T>
+bool TestAlphaBetaDivAgree(size_t N, size_t dim, size_t Rep, T alpha, T beta) {
+    vector<T> vect1(dim), vect2(dim);
+    T* pVect1 = &vect1[0]; 
+    T* pVect2 = &vect2[0];
+
+    T Dist = 0;
+    T Error = 0;
+    T TotalQty = 0;
+
+    for (size_t i = 0; i < Rep; ++i) {
+        for (size_t j = 1; j < N; ++j) {
+            GenRandVect(pVect1, dim, T(RANGE_SMALL), T(1.0), true);
+            GenRandVect(pVect2, dim, T(RANGE_SMALL), T(1.0), true);
+
+            Normalize(pVect1, dim);
+            Normalize(pVect2, dim);
+
+            T val0 = alphaBetaDivergenceSlow(pVect1, pVect2, dim, alpha, beta);
+            T val1 = alphaBetaDivergenceFast(pVect1, pVect2, dim, alpha, beta);
+
+            bool bug = false;
+
+            T AbsDiff1 = fabs(val1 - val0);
+            T RelDiff1 = AbsDiff1/max(max(fabs(val1),fabs(val0)),T(1e-18));
+
+            Error += AbsDiff1;
+            ++TotalQty;
+
+            if (RelDiff1 > 1e-5 && AbsDiff1 > 1e-5) {
+                cerr << "Bug alpha-beta Div. (1) " << typeid(T).name() << " !!! Dim = " << dim 
+                     << "alpha=" << alpha << " val0 = " << val0 << " val1 = " << val1 
+                     << " Diff: " << (val0 - val1) << " RelDiff1: " << RelDiff1 
+                     << " AbsDiff1: " << AbsDiff1 << endl;
+                bug = true;
+            }
+
+            if (bug) return false;
+        }
+    }
+
+    LOG(LIB_INFO) << typeid(T).name() << " alpha-beta div. approximation error: average absolute: " << Error / TotalQty << " avg. dist: " << Dist / TotalQty << " average relative: " << Error/Dist;
+
+
+    return true;
+}
+
 bool TestSpearmanFootruleAgree(size_t N, size_t dim, size_t Rep) {
     vector<PivotIdType> vect1(dim), vect2(dim);
     PivotIdType* pVect1 = &vect1[0]; 
@@ -1098,6 +1145,17 @@ TEST(TestAgree) {
             TestRenyiDivAgree(1024, dim, 10, alpha);
           }
 
+          for (float alpha = -2; alpha <= 2; alpha += 0.5) 
+          for (float beta = -2; beta <= 2; beta += 0.5) 
+          {
+            TestAlphaBetaDivAgree(1024, dim, 10, alpha, beta);
+          }
+
+          for (double alpha = -2; alpha <= 2; alpha += 0.5) 
+          for (double beta = -2; beta <= 2; beta += 0.5) 
+          {
+            TestAlphaBetaDivAgree(1024, dim, 10, alpha, beta);
+          }
         }
 
         nTest++;