Add pow method

boostorg · Jun 18, 2018 · 25ad8e5 · 25ad8e5
1 parent 70fe050
commit 25ad8e5
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Showing 2 changed files with 56 additions and 3 deletions.
diff --git a/include/boost/rational.hpp b/include/boost/rational.hpp
@@ -21,6 +21,7 @@
 //    Nickolay Mladenov, for the implementation of operator+=
 
 //  Revision History
+//  14 Jun 18  Add pow
 //  02 Sep 13  Remove unneeded forward declarations; tweak private helper
 //             function (Daryle Walker)
 //  30 Aug 13  Improve exception safety of "assign"; start modernizing I/O code
@@ -840,7 +841,7 @@ template <typename IntType>
 void rational<IntType>::normalize()
 {
     // Avoid repeated construction
-    IntType zero(0);
+    IntType const zero(0);
 
     if (den == zero)
        BOOST_THROW_EXCEPTION(bad_rational());
@@ -856,9 +857,8 @@ void rational<IntType>::normalize()
     num /= g;
     den /= g;
 
-    if (den < -(std::numeric_limits<IntType>::max)()) {
+    if (den < -(std::numeric_limits<IntType>::max)())
         BOOST_THROW_EXCEPTION(bad_rational("bad rational: non-zero singular denominator"));
-    }
 
     // Ensure that the denominator is positive
     if (den < zero) {
@@ -869,6 +869,23 @@ void rational<IntType>::normalize()
     BOOST_ASSERT( this->test_invariant() );
 }
 
+template <typename IntType>
+inline rational<IntType> pow(rational<IntType> base, IntType exponent)
+{
+    if (!base)
+        return base;
+    bool const positive = exponent >= 0;
+    rational<IntType> result((exponent % 2 != 0) ? base : rational<IntType>(1));
+
+    while ((exponent /= 2) != 0) {
+        base *= base;
+        if ((exponent % 2) != 0)
+            result *= base;
+    }
+
+    return positive ? result : (static_cast<IntType>(1) / result);
+}
+
 #ifndef BOOST_NO_IOSTREAM
 namespace detail {
 

diff --git a/test/rational_test.cpp b/test/rational_test.cpp
@@ -19,6 +19,7 @@
 // since he hasn't been in contact for years.)
 
 // Revision History
+// 14 Jun 18  Added pow tests
 // 30 Aug 13  Add bug-test of assignments holding the basic and/or strong
 //            guarantees (Daryle Walker)
 // 27 Aug 13  Add test for cross-version constructor template (Daryle Walker)
@@ -1605,4 +1606,39 @@ BOOST_AUTO_TEST_CASE( ticket_9067_test )
 #endif
 }
 
+// Power tests
+BOOST_AUTO_TEST_CASE_TEMPLATE( rational_pow_test, T, all_signed_test_types )
+{
+    typedef boost::rational<T> rational_type;
+
+    BOOST_CHECK_EQUAL( pow(rational_type(0), T( 0)), rational_type(0) );
+
+    BOOST_CHECK_EQUAL( pow(rational_type(2), T(-4)), rational_type(1, 16) );
+    BOOST_CHECK_EQUAL( pow(rational_type(2), T(-3)), rational_type(1, 8) );
+    BOOST_CHECK_EQUAL( pow(rational_type(2), T(-2)), rational_type(1, 4) );
+    BOOST_CHECK_EQUAL( pow(rational_type(2), T(-1)), rational_type(1, 2) );
+    BOOST_CHECK_EQUAL( pow(rational_type(2), T( 0)), rational_type(1) );
+    BOOST_CHECK_EQUAL( pow(rational_type(2), T( 1)), rational_type(2) );
+    BOOST_CHECK_EQUAL( pow(rational_type(2), T( 2)), rational_type(4) );
+    BOOST_CHECK_EQUAL( pow(rational_type(2), T( 3)), rational_type(8) );
+    BOOST_CHECK_EQUAL( pow(rational_type(2), T( 4)), rational_type(16) );
+
+    BOOST_CHECK_EQUAL( pow(rational_type(-1, 2), T(-4)), rational_type(16) );
+    BOOST_CHECK_EQUAL( pow(rational_type(-1, 2), T(-3)), rational_type(-8) );
+    BOOST_CHECK_EQUAL( pow(rational_type(-1, 2), T(-2)), rational_type(4) );
+    BOOST_CHECK_EQUAL( pow(rational_type(-1, 2), T(-1)), rational_type(-2) );
+    BOOST_CHECK_EQUAL( pow(rational_type(-1, 2), T( 0)), rational_type(1) );
+    BOOST_CHECK_EQUAL( pow(rational_type(-1, 2), T( 1)), rational_type(-1, 2) );
+    BOOST_CHECK_EQUAL( pow(rational_type(-1, 2), T( 2)), rational_type(1, 4) );
+    BOOST_CHECK_EQUAL( pow(rational_type(-1, 2), T( 3)), rational_type(-1, 8) );
+    BOOST_CHECK_EQUAL( pow(rational_type(-1, 2), T( 4)), rational_type(1, 16) );
+
+    BOOST_CHECK_EQUAL( pow(rational_type(1, 3), T(3)), rational_type(1, 27) );
+    BOOST_CHECK_EQUAL( pow(rational_type(2, 3), T(3)), rational_type(8, 27) );
+    BOOST_CHECK_EQUAL( pow(rational_type(1, 5), T(5)), rational_type(1, 3125) );
+    BOOST_CHECK_EQUAL( pow(rational_type(2, 5), T(5)), rational_type(32, 3125) );
+    BOOST_CHECK_EQUAL( pow(rational_type(3, 5), T(5)), rational_type(243, 3125) );
+    BOOST_CHECK_EQUAL( pow(rational_type(4, 5), T(5)), rational_type(1024, 3125) );
+}
+
 BOOST_AUTO_TEST_SUITE_END()