Make the RAND() and RANDBETWEEN() Calc functions non-random when requested

We don't want such a mode to affect other uses of randomness, though. Thus use
a separate random number generator object for these two functions, and use a
fixed seed for it if the SC_RAND_REPEATABLE environment variable is set.

As RAND() is implemented in sc, and RANDBETWEEN() is implemented in scaddins,
it was a bit hard to figure out where to add the new functions needed, without
having to over-engineer things with UNO. (This functionality is totally
Calc-specific, but neither sc nor scaddins has any public (non-UNO) API.)
Caolan suggested the formula module, which seems like a good enough place to
me.

Change-Id: I4b0cb327392e51a18bce28478af91b0174d6b726

1 files changed, 56 insertions, 0 deletions

diff --git a/formula/source/core/api/random.cxx b/formula/source/core/api/random.cxx
new file mode 100644
index 000000000000..727262fdffd5
--- /dev/null
+++ b/formula/source/core/api/random.cxx
@@ -0,0 +1,56 @@
+/* -*- 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/.
+ */
+
+#include <time.h>
+
+#include <random>
+
+#include <formula/random.hxx>
+#include <rtl/instance.hxx>
+
+namespace {
+
+struct CalcFormulaRandomGenerator
+{
+    std::mt19937 aRng;
+    CalcFormulaRandomGenerator()
+    {
+        // initialises the state of this RNG.
+        // should only be called once.
+        bool bRepeatable = (getenv("SC_RAND_REPEATABLE") != 0);
+        aRng.seed(bRepeatable ? 42 : time(NULL));
+    }
+};
+
+class theCalcFormulaRandomGenerator : public rtl::Static<CalcFormulaRandomGenerator, theCalcFormulaRandomGenerator> {};
+
+}
+
+namespace formula
+{
+
+namespace rng
+{
+
+double fRandom(double a, double b)
+{
+    std::uniform_real_distribution<double> dist(a, b);
+    return dist(theCalcFormulaRandomGenerator::get().aRng);
+}
+
+sal_Int32 nRandom(sal_Int32 a, sal_Int32 b)
+{
+    std::uniform_int_distribution<sal_Int32> dist(a, b);
+    return dist(theCalcFormulaRandomGenerator::get().aRng);
+}
+
+} // rng
+} // formula
+
+/* vim:set shiftwidth=4 softtabstop=4 expandtab: */