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diff --git a/sc/inc/arraysumfunctor.hxx b/sc/inc/arraysumfunctor.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/.
+ *
+ */
+
+#pragma once
+
+#include <cmath>
+#include "kahan.hxx"
+#include <formula/errorcodes.hxx>
+
+namespace sc::op
+{
+/**
+  * If no boosts available, Unrolled KahanSum.
+  */
+static inline KahanSum executeUnrolled(size_t& i, size_t nSize, const double* pCurrent)
+{
+    size_t nRealSize = nSize - i;
+    size_t nUnrolledSize = nRealSize - (nRealSize % 4);
+
+    if (nUnrolledSize > 0)
+    {
+        KahanSum sum0 = 0.0;
+        KahanSum sum1 = 0.0;
+        KahanSum sum2 = 0.0;
+        KahanSum sum3 = 0.0;
+
+        for (; i + 3 < nUnrolledSize; i += 4)
+        {
+            sum0 += *pCurrent++;
+            sum1 += *pCurrent++;
+            sum2 += *pCurrent++;
+            sum3 += *pCurrent++;
+        }
+        // We are using pairwise summation alongside Kahan
+        return (sum0 + sum1) + (sum2 + sum3);
+    }
+    return 0.0;
+}
+
+/**
+  * This function task is to choose the fastest method available to perform the sum.
+  * @param i
+  * @param nSize
+  * @param pCurrent
+  */
+static inline KahanSum executeFast(size_t& i, size_t nSize, const double* pCurrent)
+{
+#if SC_USE_SSE2
+    return executeSSE2(i, nSize, pCurrent);
+#else
+    return executeUnrolled(i, nSize, pCurrent);
+#endif
+}
+
+/**
+  * Performs the sum of an array.
+  * Note that align 16 will speed up the process.
+  * @param pArray
+  * @param nSize
+  */
+inline KahanSum sumArray(const double* pArray, size_t nSize)
+{
+    size_t i = 0;
+    const double* pCurrent = pArray;
+    KahanSum fSum = executeFast(i, nSize, pCurrent);
+
+    // sum rest of the array
+    for (; i < nSize; ++i)
+        fSum += pArray[i];
+
+    // If the sum is a NaN, some of the terms were empty cells, probably.
+    // Re-calculate, carefully
+    double fVal = fSum.get();
+    if (!std::isfinite(fVal))
+    {
+        FormulaError nErr = GetDoubleErrorValue(fVal);
+        if (nErr == FormulaError::NoValue)
+        {
+            fSum = 0;
+            for (i = 0; i < nSize; i++)
+            {
+                if (!std::isfinite(pArray[i]))
+                {
+                    nErr = GetDoubleErrorValue(pArray[i]);
+                    if (nErr != FormulaError::NoValue)
+                        fSum += pArray[i]; // Let errors encoded as NaNs propagate ???
+                }
+                else
+                    fSum += pArray[i];
+            }
+        }
+    }
+    return fSum;
+}
+
+} // end namespace sc::op
+
+/* vim:set shiftwidth=4 softtabstop=4 expandtab: */