1 files changed, 82 insertions, 0 deletions
diff --git a/sc/inc/subtotal.hxx b/sc/inc/subtotal.hxx
new file mode 100644
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+++ b/sc/inc/subtotal.hxx
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+/* -*- Mode: C++; tab-width: 4; indent-tabs-mode: nil; c-basic-offset: 4 -*- */
+/*
+ * This file is part of the LibreOffice project.
+ *
+ * This Source Code Form is subject to the terms of the Mozilla Public
+ * License, v. 2.0. If a copy of the MPL was not distributed with this
+ * file, You can obtain one at http://mozilla.org/MPL/2.0/.
+ *
+ * This file incorporates work covered by the following license notice:
+ *
+ *   Licensed to the Apache Software Foundation (ASF) under one or more
+ *   contributor license agreements. See the NOTICE file distributed
+ *   with this work for additional information regarding copyright
+ *   ownership. The ASF licenses this file to you under the Apache
+ *   License, Version 2.0 (the "License"); you may not use this file
+ *   except in compliance with the License. You may obtain a copy of
+ *   the License at http://www.apache.org/licenses/LICENSE-2.0 .
+ */
+
+#pragma once
+
+#include "global.hxx"
+
+class SubTotal
+{
+public:
+    static bool SafePlus( double& fVal1, double fVal2);
+    static bool SafeMult( double& fVal1, double fVal2);
+    static bool SafeDiv( double& fVal1, double fVal2);
+};
+
+class ScFunctionData;
+
+/** Implements the Welford Online one-pass algorithm.
+    See https://en.wikipedia.org/wiki/Algorithms_for_calculating_variance#Welford's_Online_algorithm
+    and Donald E. Knuth, TAoCP vol.2, 3rd edn., p. 232
+ */
+class WelfordRunner
+{
+public:
+    WelfordRunner() : mfMean(0.0), mfM2(0.0), mnCount(0) {}
+    void        update( double fVal );
+    sal_uInt64  getCount() const                { return mnCount; }
+    double      getVarianceSample() const       { return mnCount > 1 ? mfM2 / (mnCount-1) : 0.0; }
+    double      getVariancePopulation() const   { return mnCount > 0 ? mfM2 / mnCount : 0.0; }
+
+    // The private variables can be abused by ScFunctionData as general
+    // sum/min/max/ave/count/... variables to reduce memory footprint for that
+    // ScFunctionData may be a mass object during consolidation.
+    // ScFunctionData::update() and getResult() take care that purposes are not
+    // mixed.
+    friend class ScFunctionData;
+private:
+    double      mfMean;
+    double      mfM2;
+    sal_uInt64  mnCount;
+};
+
+/** To calculate a single subtotal function. */
+class ScFunctionData
+{
+public:
+    ScFunctionData() : meFunc(SUBTOTAL_FUNC_NONE), mbError(false) {}
+    ScFunctionData( ScSubTotalFunc eFn ) : meFunc(eFn), mbError(false) {}
+
+    void            update( double fNewVal );
+    /// Check getError() after (!) obtaining the result.
+    double          getResult();
+    bool            getError() const    { return mbError; }
+    ScSubTotalFunc  getFunc() const     { return meFunc; }
+    void            setError()          { mbError = true; }
+
+private:
+    WelfordRunner   maWelford;
+    ScSubTotalFunc  meFunc;
+    bool            mbError;
+
+    double&         getValueRef()   { return maWelford.mfMean; }
+    sal_uInt64&     getCountRef()   { return maWelford.mnCount; }
+};
+
+/* vim:set shiftwidth=4 softtabstop=4 expandtab: */