New singleton class IPrecomputed. Provides factorial[k].

Core/Tools/Precomputed.cpp

+// ************************************************************************** //
+//
+//  BornAgain: simulate and fit scattering at grazing incidence
+//
+//! @file      Tools/src/Precomputed.cpp
+//! @brief     Implements class Precomputed, providing precomputed constants
+//!
+//! @homepage  http://www.bornagainproject.org
+//! @license   GNU General Public License v3 or higher (see COPYING)
+//! @copyright Forschungszentrum Jülich GmbH 2016
+//! @authors   Scientific Computing Group at MLZ Garching
+//! @authors   J. Fisher, M. Ganeva, G. Pospelov, W. Van Herck, J. Wuttke
+//
+// ************************************************************************** //
+
+#include <cmath>
+#include "Precomputed.h"
+
+//! Precompute things upon class instantiation.
+
+Precomputed::Precomputed()
+{
+    // Precompute the factorial
+    double fac = 1;
+    for( int k=1; std::isfinite(fac); ++k ){
+        factorial.push_back( fac );
+        fac *= k;
+    }
+}

Core/Tools/Precomputed.h

+// ************************************************************************** //
+//
+//  BornAgain: simulate and fit scattering at grazing incidence
+//
+//! @file      Tools/inc/Precomputed.h
+//! @brief     Defines classes Precomputed, IPrecomputed, providing precomputed constants
+//!
+//! @homepage  http://www.bornagainproject.org
+//! @license   GNU General Public License v3 or higher (see COPYING)
+//! @copyright Forschungszentrum Jülich GmbH 2016
+//! @authors   Scientific Computing Group at MLZ Garching
+//! @authors   J. Fisher, M. Ganeva, G. Pospelov, W. Van Herck, J. Wuttke
+//
+// ************************************************************************** //
+
+#include <vector>
+#include "ISingleton.h"
+
+class Precomputed
+{
+public:
+    Precomputed();
+    std::vector<double> factorial;
+};
+
+class IPrecomputed: public ISingleton<Precomputed>
+{
+};

Tests/UnitTests/TestCore/PrecomputedTest.h

+#ifndef PRECOMPUTEDTEST_H
+#define PRECOMPUTEDTEST_H
+
+#include "Precomputed.h"
+#include "gtest/gtest.h"
+#include <memory>
+
+class PrecomputedTest : public ::testing::Test
+{
+public:
+};
+
+TEST_F(PrecomputedTest, Factorial)
+{
+    const double eps = 2.3e-16; // about the machine precision
+    auto& precomputed = IPrecomputed::instance();
+    EXPECT_TRUE(precomputed.factorial.size()>150); 
+    EXPECT_DOUBLE_EQ(precomputed.factorial[0], 1.);
+    EXPECT_DOUBLE_EQ(precomputed.factorial[1], 1.);
+    EXPECT_DOUBLE_EQ(precomputed.factorial[2], 2.);
+    EXPECT_DOUBLE_EQ(precomputed.factorial[3], 6.);
+    for( size_t k=4; k<precomputed.factorial.size(); ++k )
+        EXPECT_NEAR(precomputed.factorial[k], tgamma(k+1.), 4*eps*tgamma(k+1.) );
+}
+
+#endif

Tests/UnitTests/TestCore/main.cpp

@@ -56,6 +56,7 @@
 #include "Shape2DTest.h"
 #include "RectangularDetectorTest.h"
 #include "SpecialFunctionsTest.h"
+#include "PrecomputedTest.h"
 
 
 struct ErrorStreamRedirect {