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+///////////////////////////////////////////////////////////////////////////////
+// sum_kahan.hpp
+//
+//  Copyright 2010 Gaetano Mendola, 2011 Simon West. Distributed under the Boost
+//  Software License, Version 1.0. (See accompanying file
+//  LICENSE_1_0.txt or copy at http://www.boost.org/LICENSE_1_0.txt)
+
+#ifndef BOOST_ACCUMULATORS_STATISTICS_SUM_KAHAN_HPP_EAN_26_07_2010
+#define BOOST_ACCUMULATORS_STATISTICS_SUM_KAHAN_HPP_EAN_26_07_2010
+
+#include <boost/accumulators/framework/accumulator_base.hpp>
+#include <boost/accumulators/framework/parameters/sample.hpp>
+#include <boost/accumulators/statistics_fwd.hpp>
+#include <boost/accumulators/statistics/sum.hpp>
+#include <boost/accumulators/statistics/weighted_sum_kahan.hpp>
+#include <boost/numeric/conversion/cast.hpp>
+
+namespace boost { namespace accumulators
+{
+
+namespace impl
+{
+
+#if _MSC_VER > 1400
+# pragma float_control(push)
+# pragma float_control(precise, on)
+#endif
+
+template<typename Sample, typename Tag>
+struct sum_kahan_impl
+  : accumulator_base
+{
+    typedef Sample result_type;
+
+    ////////////////////////////////////////////////////////////////////////////
+    // sum_kahan_impl
+    /**
+        @brief Kahan summation algorithm
+
+        The Kahan summation algorithm reduces the numerical error obtained with standard
+        sequential sum.
+
+    */
+    template<typename Args>
+    sum_kahan_impl(Args const & args)
+      : sum(args[parameter::keyword<Tag>::get() | Sample()]),
+        compensation(boost::numeric_cast<Sample>(0.0))
+    {
+    }
+
+    template<typename Args>
+    void 
+#if BOOST_ACCUMULATORS_GCC_VERSION > 40305
+    __attribute__((__optimize__("no-associative-math")))
+#endif
+    operator ()(Args const & args)
+    {
+        const Sample myTmp1 = args[parameter::keyword<Tag>::get()] - this->compensation;
+        const Sample myTmp2 = this->sum + myTmp1;
+        this->compensation = (myTmp2 - this->sum) - myTmp1;
+        this->sum = myTmp2;
+    }
+
+    result_type result(dont_care) const
+    {
+      return this->sum;
+    }
+
+private:
+    Sample sum;
+    Sample compensation;
+};
+
+#if _MSC_VER > 1400
+# pragma float_control(pop)
+#endif
+
+} // namespace impl
+
+///////////////////////////////////////////////////////////////////////////////
+// tag::sum_kahan
+// tag::sum_of_weights_kahan
+// tag::sum_of_variates_kahan
+//
+namespace tag
+{
+
+    struct sum_kahan
+      : depends_on<>
+    {
+        /// INTERNAL ONLY
+        ///
+        typedef impl::sum_kahan_impl< mpl::_1, tag::sample > impl;
+    };
+
+    struct sum_of_weights_kahan
+      : depends_on<>
+    {
+        typedef mpl::true_ is_weight_accumulator;
+        /// INTERNAL ONLY
+        ///
+        typedef accumulators::impl::sum_kahan_impl<mpl::_2, tag::weight> impl;
+    };
+
+    template<typename VariateType, typename VariateTag>
+    struct sum_of_variates_kahan
+      : depends_on<>
+    {
+        /// INTERNAL ONLY
+        ///
+        typedef mpl::always<accumulators::impl::sum_kahan_impl<VariateType, VariateTag> > impl;
+    };
+
+} // namespace tag
+
+///////////////////////////////////////////////////////////////////////////////
+// extract::sum_kahan
+// extract::sum_of_weights_kahan
+// extract::sum_of_variates_kahan
+//
+namespace extract
+{
+    extractor<tag::sum_kahan> const sum_kahan = {};
+    extractor<tag::sum_of_weights_kahan> const sum_of_weights_kahan = {};
+    extractor<tag::abstract_sum_of_variates> const sum_of_variates_kahan = {};
+
+    BOOST_ACCUMULATORS_IGNORE_GLOBAL(sum_kahan)
+    BOOST_ACCUMULATORS_IGNORE_GLOBAL(sum_of_weights_kahan)
+    BOOST_ACCUMULATORS_IGNORE_GLOBAL(sum_of_variates_kahan)
+} // namespace extract
+
+using extract::sum_kahan;
+using extract::sum_of_weights_kahan;
+using extract::sum_of_variates_kahan;
+
+// sum(kahan) -> sum_kahan
+template<>
+struct as_feature<tag::sum(kahan)>
+{
+    typedef tag::sum_kahan type;
+};
+
+// sum_of_weights(kahan) -> sum_of_weights_kahan
+template<>
+struct as_feature<tag::sum_of_weights(kahan)>
+{
+    typedef tag::sum_of_weights_kahan type;
+};
+
+// So that sum_kahan can be automatically substituted with
+// weighted_sum_kahan when the weight parameter is non-void.
+template<>
+struct as_weighted_feature<tag::sum_kahan>
+{
+    typedef tag::weighted_sum_kahan type;
+};
+
+template<>
+struct feature_of<tag::weighted_sum_kahan>
+  : feature_of<tag::sum>
+{};
+
+// for the purposes of feature-based dependency resolution,
+// sum_kahan provides the same feature as sum
+template<>
+struct feature_of<tag::sum_kahan>
+  : feature_of<tag::sum>
+{
+};
+
+// for the purposes of feature-based dependency resolution,
+// sum_of_weights_kahan provides the same feature as sum_of_weights
+template<>
+struct feature_of<tag::sum_of_weights_kahan>
+  : feature_of<tag::sum_of_weights>
+{
+};
+
+template<typename VariateType, typename VariateTag>
+struct feature_of<tag::sum_of_variates_kahan<VariateType, VariateTag> >
+  : feature_of<tag::abstract_sum_of_variates>
+{
+};
+
+}} // namespace boost::accumulators
+
+#endif
+