diff --git a/FPSim2/src/sim.cpp b/FPSim2/src/sim.cpp
index 86dd7e2..42c106e 100644
--- a/FPSim2/src/sim.cpp
+++ b/FPSim2/src/sim.cpp
@@ -8,16 +8,6 @@
 
 namespace py = pybind11;
 
-inline uint32_t SubstructCoeff(const uint32_t &rel_co_popcnt,
-                               const uint32_t &common_popcnt)
-{
-    uint32_t coeff = 0;
-    coeff = rel_co_popcnt + common_popcnt;
-    if (coeff != 0)
-        coeff = common_popcnt / coeff;
-    return coeff;
-}
-
 py::array_t<uint32_t> SubstructureScreenout(const py::array_t<uint64_t> py_query,
                                             const py::array_t<uint64_t> py_db,
                                             const uint32_t start,
@@ -35,21 +25,20 @@ py::array_t<uint32_t> SubstructureScreenout(const py::array_t<uint64_t> py_query
 
     auto results = new std::vector<uint32_t>();
 
-    uint32_t coeff;
-    uint64_t common_popcnt = 0;
-    uint64_t rel_co_popcnt = 0;
-    for (auto i = start; i < end; i++, dbptr += fp_shape,
-              common_popcnt = 0, rel_co_popcnt = 0)
+    // Substructure match requires all query bits to be present in db entry
+    for (auto i = start; i < end; i++, dbptr += fp_shape)
     {
+        bool is_match = true;
         for (size_t j = 1; j < popcnt_idx; j++)
         {
-            common_popcnt += popcntll(qptr[j] & dbptr[j]);
-            rel_co_popcnt += popcntll(qptr[j] & ~dbptr[j]);
+            // Early termination: if any query bit is not in db, skip the entry
+            if (qptr[j] & ~dbptr[j])
+            {
+                is_match = false;
+                break;
+            }
         }
-        // calc optimised tversky with a=1, b=0
-        coeff = SubstructCoeff(rel_co_popcnt, common_popcnt);
-
-        if (coeff == 1)
+        if (is_match)
             results->push_back((uint32_t)dbptr[0]);
     }
     // acquire the GIL before calling Python code
@@ -57,18 +46,6 @@ py::array_t<uint32_t> SubstructureScreenout(const py::array_t<uint64_t> py_query
     return utils::Vector2NumPy<uint32_t>(results);
 }
 
-inline float TverskyCoeff(const uint32_t &common_popcnt,
-                          const uint32_t &rel_co_popcnt,
-                          const uint32_t &rel_co_popcnt2,
-                          const float &a, const float &b)
-{
-    float coeff = 0.0;
-    coeff = common_popcnt + a * rel_co_popcnt + b * rel_co_popcnt2;
-    if (coeff != 0.0)
-        coeff = common_popcnt / coeff;
-    return coeff;
-}
-
 py::array_t<Result> TverskySearch(const py::array_t<uint64_t> py_query,
                                   const py::array_t<uint64_t> py_db,
                                   const float threshold,
@@ -86,24 +63,25 @@ py::array_t<Result> TverskySearch(const py::array_t<uint64_t> py_query,
 
     const auto fp_shape = query.shape(0);
     const auto popcnt_idx = fp_shape - 1;
+    const auto q_popcnt = qptr[popcnt_idx];
+
+    const float one_minus_a_minus_b = 1.0f - a - b;
+    const float a_times_q = a * q_popcnt;
 
     auto results = new std::vector<Result>();
 
-    float coeff;
-    uint64_t common_popcnt = 0;
-    uint64_t rel_co_popcnt = 0;
-    uint64_t rel_co_popcnt2 = 0;
-    for (auto i = start; i < end; i++, dbptr += fp_shape,
-              common_popcnt = 0, rel_co_popcnt = 0, rel_co_popcnt2 = 0)
+    for (auto i = start; i < end; i++, dbptr += fp_shape)
     {
+        const auto db_popcnt = dbptr[popcnt_idx];
+
+        uint64_t common_popcnt = 0;
         for (auto j = 1; j < popcnt_idx; j++)
-        {
-            // popcnts of both relative complements and intersection
             common_popcnt += popcntll(qptr[j] & dbptr[j]);
-            rel_co_popcnt += popcntll(qptr[j] & ~dbptr[j]);
-            rel_co_popcnt2 += popcntll(dbptr[j] & ~qptr[j]);
-        }
-        coeff = TverskyCoeff(common_popcnt, rel_co_popcnt, rel_co_popcnt2, a, b);
+
+        // Tversky: common / (common*(1-a-b) + a*q_popcnt + b*db_popcnt)
+        float denom = common_popcnt * one_minus_a_minus_b + a_times_q + b * db_popcnt;
+        float coeff = (denom != 0.0f) ? common_popcnt / denom : 0.0f;
+
         if (coeff >= threshold)
             results->push_back({i, (uint32_t)dbptr[0], coeff});
     }