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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;
}
}}