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Added more general power functionality as requested by Sean Parent. Also added enable_if to make sure the exponent is an integral type.

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Marshall Clow
2014-12-03 15:15:15 -08:00
parent 85adf4c74e
commit d4734356e9
4 changed files with 91 additions and 31 deletions
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70
include/boost/algorithm/algorithm.hpp
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@ -18,32 +18,68 @@
#define BOOST_ALGORITHM_HPP
#include <boost/utility/enable_if.hpp> // for boost::disable_if
#include <boost/type_traits/is_integral.hpp>
namespace boost { namespace algorithm {
template <typename T>
T identity_operation ( std::multiplies<T> ) { return T(1); }
template <typename T>
T identity_operation ( std::plus<T> ) { return T(0); }
/// \fn power ( T x, Integer n )
/// \return the value "x" raised to the power "n"
///
/// \param x The value to be exponentiated
/// \param n The exponent
/// \param n The exponent (must be >= 0)
///
// \remark Taken from Knuth, The Art of Computer Programming, Volume 2:
// Seminumerical Algorithms, Section 4.6.3
// \remark Taken from Knuth, The Art of Computer Programming, Volume 2:
// Seminumerical Algorithms, Section 4.6.3
template <typename T, typename Integer>
T power (T x, Integer n) {
T y = 1; // Should be "T y{1};"
if (n == 0) return y;
while (true) {
if (n % 2 == 1) {
y = x * y;
if (n == 1)
return y;
}
n = n / 2;
x = x * x;
}
return y;
}
typename boost::enable_if<boost::is_integral<Integer>, T>::type
power (T x, Integer n) {
T y = 1; // Should be "T y{1};"
if (n == 0) return y;
while (true) {
if (n % 2 == 1) {
y = x * y;
if (n == 1)
return y;
}
n = n / 2;
x = x * x;
}
return y;
}
/// \fn power ( T x, Integer n, Operation op )
/// \return the value "x" raised to the power "n"
/// using the operaton "op".
///
/// \param x The value to be exponentiated
/// \param n The exponent (must be >= 0)
/// \param op The operation used
///
// \remark Taken from Knuth, The Art of Computer Programming, Volume 2:
// Seminumerical Algorithms, Section 4.6.3
template <typename T, typename Integer, typename Operation>
typename boost::enable_if<boost::is_integral<Integer>, T>::type
power (T x, Integer n, Operation op) {
T y = identity_operation(op);
if (n == 0) return y;
while (true) {
if (n % 2 == 1) {
y = op(x, y);
if (n == 1)
return y;
}
n = n / 2;
x = op(x, x);
}
return y;
}
}}

1
test/Jamfile.v2
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@ -30,6 +30,7 @@ alias unit_test_framework
# Misc tests
[ run clamp_test.cpp unit_test_framework : : : : clamp_test ]
[ run power_test.cpp unit_test_framework : : : : power_test ]
[ compile-fail power_fail1.cpp : : : : ]
# Cxx11 tests
[ run all_of_test.cpp unit_test_framework : : : : all_of_test ]

24
test/power_fail1.cpp Normal file
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@ -0,0 +1,24 @@
/*
Copyright (c) Marshall Clow 2014.
Distributed under 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)
For more information, see http://www.boost.org
*/
#include <iostream>
#include <boost/config.hpp>
#include <boost/algorithm/algorithm.hpp>
#define BOOST_TEST_MAIN
#include <boost/test/unit_test.hpp>
namespace ba = boost::algorithm;
BOOST_AUTO_TEST_CASE( test_main )
{
// Second argument must be an integral value
BOOST_CHECK ( ba::power(1, 1.0) == 1);
}

27
test/power_test.cpp
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@ -15,22 +15,21 @@
#define BOOST_TEST_MAIN
#include <boost/test/unit_test.hpp>
#include <string>
#include <vector>
#include <list>
namespace ba = boost::algorithm;
BOOST_AUTO_TEST_CASE( test_main )
{
BOOST_CHECK ( ba::power(0, 0) == 1);
BOOST_CHECK ( ba::power(5, 0) == 1);
BOOST_CHECK ( ba::power(1, 1) == 1);
BOOST_CHECK ( ba::power(1, 4) == 1);
BOOST_CHECK ( ba::power(3, 2) == 9);
BOOST_CHECK ( ba::power(2, 3) == 8);
BOOST_CHECK ( ba::power(3, 3) == 27);
BOOST_CHECK ( ba::power(2, 30) == 0x40000000);
BOOST_CHECK ( ba::power(5L, 10) == 3125*3125);
BOOST_CHECK ( ba::power(18, 3) == 18*18*18);
BOOST_CHECK ( ba::power(0, 0) == 1);
BOOST_CHECK ( ba::power(5, 0) == 1);
BOOST_CHECK ( ba::power(1, 1) == 1);
BOOST_CHECK ( ba::power(1, 4) == 1);
BOOST_CHECK ( ba::power(3, 2) == 9);
BOOST_CHECK ( ba::power(2, 3) == 8);
BOOST_CHECK ( ba::power(3, 3) == 27);
BOOST_CHECK ( ba::power(2, 30) == 0x40000000);
BOOST_CHECK ( ba::power(5L, 10) == 3125*3125);
BOOST_CHECK ( ba::power(18, 3) == 18*18*18);
BOOST_CHECK ( ba::power(3,2) == ba::power(3,2, std::multiplies<int>()));
BOOST_CHECK ( ba::power(3,2, std::plus<int>()) == 6);
}