Patch for Implementation of tf-idf scheme(basic scheme in SMART)

gistfile1.cpp

diff --git a/xapian-core/include/xapian/weight.h b/xapian-core/include/xapian/weight.h
index 09cbe46..0d9a3ac 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
diff --git a/xapian-core/weight/tf_idf.cc b/xapian-core/weight/tf_idf.cc
index e69de29..d0fb9c9 100644
--- a/xapian-core/weight/tf_idf.cc
+++ b/xapian-core/weight/tf_idf.cc
@@ -0,0 +1,99 @@
+/** @file it_idfweight.cc
+ * @brief Xapian::TradWeight class - tf-idf weighting scheme
+ */
+/* Copyright (C) 2012 Jiuding Duan
+ *
+ * This program is free software; you can redistribute it and/or
+ * modify it under the terms of the GNU General Public License as
+ * published by the Free Software Foundation; either version 2 of the
+ * License, or (at your option) any later version.
+ *
+ * This program is distributed in the hope that it will be useful
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
+ * GNU General Public License for more details.
+ *
+ * You should have received a copy of the GNU General Public License
+ * along with this program; if not, write to the Free Software
+ * Foundation, Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA
+ */
+
+#include <config.h>
+
+#include <xapian/weight.h>
+
+#include "debuglog.h"
+#include "omassert.h"
+#include "serialise-double.h"
+
+#include "xapian/error.h"
+
+#include <cmath>
+
+using namespace std;
+
+namespace Xapian {
+
+Tf_idfWeight *
+Tf_idfWeight::clone() const
+{
+    return new Tf_idfWeight();
+}
+
+void
+Tf_idfWeight::init(double factor)
+{
+    Xapian::doccount tf = get_termfreq();
+    Xapian::doccount N = get_collection_size();
+
+    idf =  log(N/tf);
+}
+
+string
+Tf_idfWeight::name() const
+{
+    return "Xapian::Tf_idfWeight";
+}
+
+string
+Tf_idfWeight::serialise() const
+{
+    return string();
+}
+
+Tf_idfWeight *
+Tf_idfWeight::unserialise(const string &) const
+{
+    return new Tf_idfWeight;
+}
+
+double
+Tf_idfWeight::get_sumpart(Xapian::termcount wdf, Xapian::termcount len)
+const
+{
+    double wdf_double(wdf);
+    return wdf_double * idf;
+}
+
+double
+Tf_idfWeight::get_maxpart() const
+{
+    double wdf_max(max(get_wdf_upper_bound(),Xapian::termcount(1)));
+    return wdf_max * idf;
+}
+
+double
+Tf_idfWeight::get_sumextra(Xapian::termcount) const
+{
+    return 0;
+}
+
+double
+Tf_idfWeight::get_maxextra() const
+{
+    return 0;
+}
+
+}
+
+
diff --git a/xapian-core/weight/tf_idfweight.cc b/xapian-core/weight/tf_idfweight.cc
deleted file mode 100644
index e69de29..0000000