✨ Added a function to round a number to n decimal places (#189)

* ✨ small function to round numbers to ``n`` decimal places.

* ✅ test added.

* 🎨 implemented Marcel's suggestions.

* 🎨 make use of new function in ``energy_distribution``.

include/fiction/algorithms/simulation/sidb/energy_distribution.hpp

@@ -6,6 +6,7 @@
 #define FICTION_ENERGY_DISTRIBUTION_HPP
 
 #include "fiction/technology/charge_distribution_surface.hpp"
+#include "fiction/utils/math_utils.hpp"
 
 #include <cmath>
 #include <cstdint>
@@ -34,8 +35,7 @@ std::map<double, uint64_t> energy_distribution(const std::vector<charge_distribu
 
     for (const auto& lyt : input_vec)
     {
-        const auto energy =
-            std::round(lyt.get_system_energy() * 1'000'000) / 1'000'000;  // rounding to 6 decimal places.
+        const auto energy = round_to_n_decimal_places(lyt.get_system_energy(), 6);  // rounding to 6 decimal places.
 
         distribution[energy]++;
     }

include/fiction/utils/math_utils.hpp

@@ -0,0 +1,32 @@
+//
+// Created by Jan Drewniok on 19.04.23.
+//
+
+#ifndef FICTION_MATH_UTILS_HPP
+#define FICTION_MATH_UTILS_HPP
+
+#include <cmath>
+#include <cstdint>
+
+namespace fiction
+{
+
+/**
+ * Rounds a number to a specified number of decimal places.
+ *
+ * @tparam T the type of the number to round.
+ * @param number the number to round.
+ * @param n the number of decimal places to round to.
+ * @return the number rounded to n decimal places.
+ */
+template <typename T>
+T round_to_n_decimal_places(const T number, const uint64_t n)
+{
+    static_assert(std::is_arithmetic_v<T>, "T is not a number type");
+    const T factor = std::pow(10, n);
+    return std::round(number * factor) / factor;
+}
+
+}  // namespace fiction
+
+#endif  // FICTION_MATH_UTILS_HPP

test/utils/math_utils.cpp

@@ -0,0 +1,50 @@
+//
+// Created by Jan Drewniok on 19.04.23.
+//
+
+#include <catch2/catch_test_macros.hpp>
+
+#include <fiction/utils/math_utils.hpp>
+
+using namespace fiction;
+
+TEST_CASE("round_to_n_decimal_places should round an input number to n decimal places", "[round_to_n_decimal_places]")
+{
+    SECTION("int64_t")
+    {
+        CHECK(round_to_n_decimal_places(-1LL, 0) == -1LL);
+        CHECK(round_to_n_decimal_places(-1LL, 10) == -1LL);
+        CHECK(round_to_n_decimal_places(1LL, 0) == 1LL);
+        CHECK(round_to_n_decimal_places(1LL, 10) == 1LL);
+    }
+
+    SECTION("double")
+    {
+        const double value_positive = 3.145926;
+        CHECK(round_to_n_decimal_places(value_positive, 0) == 3);
+        CHECK(round_to_n_decimal_places(value_positive, 1) == 3.1);
+        CHECK(round_to_n_decimal_places(value_positive, 2) == 3.15);
+        CHECK(round_to_n_decimal_places(value_positive, 3) == 3.146);
+        CHECK(round_to_n_decimal_places(value_positive, 4) == 3.1459);
+        CHECK(round_to_n_decimal_places(value_positive, 5) == 3.14593);
+        CHECK(round_to_n_decimal_places(value_positive, 6) == 3.145926);
+
+        const double value_negative = -3.145926;
+        CHECK(round_to_n_decimal_places(value_negative, 0) == -3);
+        CHECK(round_to_n_decimal_places(value_negative, 1) == -3.1);
+        CHECK(round_to_n_decimal_places(value_negative, 2) == -3.15);
+        CHECK(round_to_n_decimal_places(value_negative, 3) == -3.146);
+        CHECK(round_to_n_decimal_places(value_negative, 4) == -3.1459);
+        CHECK(round_to_n_decimal_places(value_negative, 5) == -3.14593);
+        CHECK(round_to_n_decimal_places(value_negative, 6) == -3.145926);
+    }
+
+    SECTION("Edge cases")
+    {
+        CHECK(round_to_n_decimal_places(1.005, 2) == 1.0);
+        CHECK(round_to_n_decimal_places(0.000001, 6) == 0.000001);
+        CHECK(round_to_n_decimal_places(0.0000001, 6) == 0);
+        CHECK(round_to_n_decimal_places(-0.000001, 6) == -0.000001);
+        CHECK(round_to_n_decimal_places(-0.0000001, 6) == 0);
+    }
+}