Define subclass tf-idf for weighting scheme

gistfile1.cpp

diff --git a/xapian-core/include/xapian/weight.h b/xapian-core/include/xapian/weight.h
index 09cbe46..7592af1 100644
--- a/xapian-core/include/xapian/weight.h
+++ b/xapian-core/include/xapian/weight.h
@@ -506,6 +506,51 @@ class XAPIAN_VISIBILITY_DEFAULT TradWeight : public Weight {
     double get_maxextra() const;
 };
 
+/** Xapian::Weight subclass implementing the basic tf-idf scheme
+ *
+ *  This class implements the basic tf-idf Weighting scheme, as
+ *  described in SMART, the corresponding parameters string in 
+ *  SMART is nnn. That means:
+ *  new-tf = tf.
+ *  new-wt = new-tf.
+ *  norm-weight = new-wt.
+ *  no parameter in this basic implenmentation, in the future,
+ *  parameter can be used to specify the different re-computation of
+ *  tf, df and normalization of entire subvector.  
+*/
+class XAPIAN_VISIBILITY_DEFAULT Tf_idfWeight : public Weight {
+    /// idf.
+    mutable double idf;
+
+    Tf_idfWeight * clone() const;
+
+    void init(double factor);
+
+  public:
+    /** Construct a tf-idf weight.
+     *  add parameters to specify different re-computation
+     *  in the future.
+     */
+    Tf_idfWeight() {
+	need_stat(COLLECTION_SIZE);
+	need_stat(TERMFREQ);
+	need_stat(WDF);
+	need_stat(WDF_MAX);
+    }
+
+    std::string name() const;
+
+    std::string serialise() const;
+    Tf_idfWeight * unserialise(const std::string & s) const;
+
+    double get_sumpart(Xapian::termcount wdf,
+			Xapian::termcount doclen) const;
+    double get_maxpart() const;
+
+    double get_sumextra(Xapian::termcount doclen) const;
+    double get_maxextra() const;
+};
+
 }
 
 #endif // XAPIAN_INCLUDED_WEIGHT_H