Merge pull request #9828 from vespa-engine/geirst/bm25-feature-optimize-inner-loop

Reduce number of math operations in inner loop of bm25 feature.

2 files changed, 14 insertions, 10 deletions

diff --git a/searchlib/src/vespa/searchlib/features/bm25_feature.cpp b/searchlib/src/vespa/searchlib/features/bm25_feature.cpp
index 6e889b48343..f2114e4705d 100644
--- a/searchlib/src/vespa/searchlib/features/bm25_feature.cpp
+++ b/searchlib/src/vespa/searchlib/features/bm25_feature.cpp
@@ -47,8 +47,8 @@ Bm25Executor::Bm25Executor(const fef::FieldInfo& field,
     : FeatureExecutor(),
       _terms(),
       _avg_field_length(avg_field_length),
-      _k1_param(k1_param),
-      _b_param(b_param)
+      _k1_mul_b(k1_param * b_param),
+      _k1_mul_one_minus_b(k1_param * (1 - b_param))
 {
     for (size_t i = 0; i < env.getNumTerms(); ++i) {
         const ITermData* term = env.getTerm(i);
@@ -56,7 +56,8 @@ Bm25Executor::Bm25Executor(const fef::FieldInfo& field,
             const ITermFieldData& term_field = term->field(j);
             if (field.id() == term_field.getFieldId()) {
                 _terms.emplace_back(term_field.getHandle(MatchDataDetails::Cheap),
-                                    get_inverse_document_frequency(term_field, env, *term));
+                                    get_inverse_document_frequency(term_field, env, *term),
+                                    k1_param);
             }
         }
     }
@@ -86,8 +87,8 @@ Bm25Executor::execute(uint32_t doc_id)
             feature_t num_occs = term.tfmd->getNumOccs();
             feature_t norm_field_length = ((feature_t)term.tfmd->getFieldLength()) / _avg_field_length;
 
-            feature_t numerator = term.inverse_doc_freq * num_occs * (_k1_param + 1);
-            feature_t denominator = num_occs + (_k1_param * (1 - _b_param + (_b_param * norm_field_length)));
+            feature_t numerator = num_occs * term.idf_mul_k1_plus_one;
+            feature_t denominator = num_occs + (_k1_mul_one_minus_b + _k1_mul_b * norm_field_length);
 
             score += numerator / denominator;
         }
diff --git a/searchlib/src/vespa/searchlib/features/bm25_feature.h b/searchlib/src/vespa/searchlib/features/bm25_feature.h
index 533c7487a2f..0afd14e7ac8 100644
--- a/searchlib/src/vespa/searchlib/features/bm25_feature.h
+++ b/searchlib/src/vespa/searchlib/features/bm25_feature.h
@@ -13,11 +13,11 @@ private:
     struct QueryTerm {
         fef::TermFieldHandle handle;
         const fef::TermFieldMatchData* tfmd;
-        double inverse_doc_freq;
-        QueryTerm(fef::TermFieldHandle handle_, double inverse_doc_freq_)
+        double idf_mul_k1_plus_one;
+        QueryTerm(fef::TermFieldHandle handle_, double inverse_doc_freq, double k1_param)
             : handle(handle_),
               tfmd(nullptr),
-              inverse_doc_freq(inverse_doc_freq_)
+              idf_mul_k1_plus_one(inverse_doc_freq * (k1_param + 1))
         {}
     };
 
@@ -25,8 +25,11 @@ private:
 
     QueryTermVector _terms;
     double _avg_field_length;
-    double _k1_param; // Determines term frequency saturation characteristics.
-    double _b_param;  // Adjusts the effects of the field length of the document matched compared to the average field length.
+
+    // The 'k1' param determines term frequency saturation characteristics.
+    // The 'b' param adjusts the effects of the field length of the document matched compared to the average field length.
+    double _k1_mul_b;
+    double _k1_mul_one_minus_b;
 
 public:
     Bm25Executor(const fef::FieldInfo& field,