From 87759391d884e61d1151029432f382959ff4c0bc Mon Sep 17 00:00:00 2001
From: Tobias Berger <berger@edv-ermtraud.net>
Date: Tue, 21 Sep 2021 11:42:53 +0200
Subject: [PATCH] pow

---
 fraction.cpp         | 41 ++++++++++++++++++++++++++++++++++++++++-
 fraction.hpp         |  7 +++++++
 tst_fractiontest.cpp | 41 +++++++++++++++++++++++++++++++++++++++++
 3 files changed, 88 insertions(+), 1 deletion(-)

diff --git a/fraction.cpp b/fraction.cpp
index 44dd38a..ea1e5fe 100644
--- a/fraction.cpp
+++ b/fraction.cpp
@@ -1,7 +1,8 @@
 #include "fraction.hpp"
 
-namespace FractionNS {
+#include <QtMath>
 
+namespace FractionNS {
   int gcd(int p, int q) {
     if(p < 0) p = -p;
     if(q < 0) q = -q;
@@ -270,6 +271,44 @@ namespace FractionNS {
     return *this;
   }
 
+  double Fraction::pow(const int n) const {
+    if(n == 0) {
+      if(m_numerator == 0) {
+        throw not_defined_error();
+      }
+      return 1.0;
+    }
+    if(n < 0) {
+      if(m_numerator == 0) {
+        throw not_real_error();
+      }
+      if(n == -1) {
+        return double(m_denominator) / m_numerator;
+      }
+
+      return qPow(double(m_denominator) / m_numerator, -n);
+    }
+    return qPow(double(m_numerator) / m_denominator, n);
+  }
+  double Fraction::pow(const Fraction& other) const {
+    if(other == 0) {
+      if(m_numerator == 0) {
+        throw not_defined_error();
+      }
+      return 1.0;
+    }
+    if(other < 0) {
+      if(m_numerator == 0) {
+        throw not_real_error();
+      }
+      if(other == -1) {
+        return double(m_denominator) / m_numerator;
+      }
+      return qPow(double(m_denominator) / m_numerator, -other.toDouble());
+    }
+    return qPow(double(m_numerator) / m_denominator, other.toDouble());
+  }
+
   Fraction& Fraction::operator-() const {
     return *new Fraction(-m_numerator, m_denominator);
   }
diff --git a/fraction.hpp b/fraction.hpp
index 6f6dcb1..91c169b 100644
--- a/fraction.hpp
+++ b/fraction.hpp
@@ -86,6 +86,13 @@ namespace FractionNS {
     Fraction& operator/=(const int);
     Fraction& operator/=(const Fraction&);
 
+    // Maybe replace with ^ operator, as it's unused for this class.
+    // Might be syntactically not-so-nice though?
+    // Python uses / for combining paths, does cpp do something similar anywhere?
+    // How does one raise a Fraction to a power while keeping it a Fraction (avoid double return type)
+    double pow(const int) const;
+    double pow(const Fraction&) const;
+
     // Unary operators
     Fraction& operator-() const;
     Fraction& operator+() const; // Should return a copy of the Fraction.
diff --git a/tst_fractiontest.cpp b/tst_fractiontest.cpp
index 228f174..16a3aed 100644
--- a/tst_fractiontest.cpp
+++ b/tst_fractiontest.cpp
@@ -29,6 +29,7 @@ private slots:
   void test_less_than_or_equal();
   void test_greater_than_or_equal();
   void test_inverse();
+  void test_pow();
 };
 
 FractionTest::FractionTest() {
@@ -442,6 +443,46 @@ void FractionTest::test_inverse() {
   QVERIFY(threw_divide_by_zero_error);
 }
 
+void FractionTest::test_pow() {
+  const Fraction f1 = Fraction(2, 3);
+  const Fraction f2 = Fraction(3, 2);
+  const Fraction f3 = Fraction(4, 9);
+  const Fraction f4 = Fraction(9, 4);
+
+  QCOMPARE(f3, f1.pow(2));
+  QCOMPARE(f4, f2.pow(2));
+
+  const Fraction f5 = Fraction(9);
+  const Fraction f6 = Fraction(1, 9);
+  const Fraction f7 = Fraction(1, 81);
+  // x ** -y = (1 / x) ** y
+  QCOMPARE(f6, f5.pow(-1));
+  QCOMPARE(f7, f5.pow(-2));
+
+  const Fraction f8 = Fraction(16);
+  // x ** (1/y) = root_y(x)
+  QCOMPARE(f8.pow(Fraction(1, 2)), 4.0);
+
+  // x ** 0 = 1; (where x != 0 and x ∈ R)
+  // 0 ** 0 depends on context
+  QCOMPARE(f1.pow(0), 1.0);
+  bool threw_correct_error = false;
+  try {
+    Fraction(0, 2).pow(0);
+  }  catch (const not_defined_error&) {
+    threw_correct_error = true;
+  }
+  QVERIFY(threw_correct_error);
+
+  threw_correct_error = false;
+  try {
+    Fraction(0, 1).pow(-1);
+  }  catch (const not_real_error&) {
+    threw_correct_error = true;
+  }
+  QVERIFY(threw_correct_error);
+}
+
 QTEST_APPLESS_MAIN(FractionTest)
 
 #include "tst_fractiontest.moc"