Cubic roots (#703)

reporting/performance/cubic_roots_performance.cpp

@@ -0,0 +1,40 @@
+//  (C) Copyright Nick Thompson 2021.
+//  Use, modification and distribution are subject to 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)
+
+#include <random>
+#include <array>
+#include <vector>
+#include <iostream>
+#include <benchmark/benchmark.h>
+#include <boost/math/tools/cubic_roots.hpp>
+
+using boost::math::tools::cubic_roots;
+
+template<class Real>
+void CubicRoots(benchmark::State& state)
+{
+    std::random_device rd;
+    auto seed = rd();
+    // This seed generates 3 real roots:
+    //uint32_t seed = 416683252;
+    std::mt19937_64 mt(seed);
+    std::uniform_real_distribution<Real> unif(-10, 10);
+
+    Real a = unif(mt);
+    Real b = unif(mt);
+    Real c = unif(mt);
+    Real d = unif(mt);
+    for (auto _ : state)
+    {
+        auto roots = cubic_roots(a,b,c,d);
+        benchmark::DoNotOptimize(roots[0]);
+    }
+}
+
+BENCHMARK_TEMPLATE(CubicRoots, float);
+BENCHMARK_TEMPLATE(CubicRoots, double);
+BENCHMARK_TEMPLATE(CubicRoots, long double);
+
+BENCHMARK_MAIN();