triangle: iteration 1

cpp/triangle/triangle.cpp

@@ -0,0 +1,65 @@
+#include "triangle.h"
+
+#include <cmath>
+#include <limits>
+#include <stdexcept>
+
+namespace triangle {
+
+using namespace std;
+
+namespace {
+
+
+inline bool fuzzy_equal(double a, double b)
+{
+    typedef numeric_limits<double> limits_t;
+
+    static const double &epsilon     = limits_t::epsilon();
+    static const double &min         = limits_t::min();
+    static const double &round_error = limits_t::round_error();
+
+
+    return abs(a - b) < epsilon * abs(a + b) * round_error
+        || abs(a - b) < min;
+}
+
+inline bool is_valid(double a, double b, double c)
+{
+    return a > 0 && b > 0 && c > 0
+        && a + b > c
+        && a + c > b
+        && b + c > a;
+}
+
+inline bool is_equilateral(double a, double b, double c)
+{
+    return fuzzy_equal(a, b)
+        && fuzzy_equal(a, c)
+        && fuzzy_equal(b, c);
+}
+
+inline bool is_isosceles(double a, double b, double c)
+{
+    return fuzzy_equal(a, b)
+        || fuzzy_equal(a, c)
+        || fuzzy_equal(b, c);
+}
+
+}
+
+kind_t kind(double a, double b, double c)
+{
+    if (!is_valid(a, b, c))
+        throw domain_error("invalid triangle");
+
+    if (is_equilateral(a, b, c))
+        return equilateral;
+
+    if (is_isosceles(a, b, c))
+        return isosceles;
+
+    return scalene;
+}
+
+}