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src/stl/_power.hpp

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#ifndef _INSTIGATE_STL_INTERNAL_HEADER_IN_ALGORITHM
#error This is an internal header file used to implement Instigate STL.\
        It should never be included directly by a program.
#endif

#ifndef INSTIGATE_STL_POWER_HPP
#define INSTIGATE_STL_POWER_HPP

// Headers from this project
#include "concept.hpp"
#include "_basis.hpp"

// Headers from other project

// Headers from standard library
#include <cassert>

// Forward declaration
namespace instigate {
        namespace stl {
                template <typename T, typename I>
                inline T power(T, I);

                template <typename T, typename I, typename M>
                inline T power(T, I, M);

                namespace implementation {
                        template <typename T, typename I, typename M>
                        T power_aux(T, I, M);
                }
        }
}

template <typename T, typename I>
inline T instigate::stl::power(T a, I n)
{
        assert(0 <= n);
        return implementation::power_aux(a, n, stl::multiplies<T>());
}

template <typename T, typename I, typename M>
inline T instigate::stl::power(T a, I n, M o)
{
        CHECK(stl::binary_function::requirements<M>);
        assert(0 <= n);
        return implementation::power_aux(a, n, o);
}

template <typename T, typename I, typename M>
inline T instigate::stl::implementation::power_aux(T a, I n, M o)
{
        char p[sizeof(T)];
        T* r = 0;
        assign(r, initialize<T>(p));
        assert(0 != r);
        if (equal(0, n)) {
                assign(*r, 1);
                return *r;
        } else {
                while (equal(0, (n & 1))) { 
                        n >>= 1;
                        assign(a, invoke(o, a, a));
                }
                assign(*r, a);
                n >>= 1;
                while (!equal(0, n)) {
                        assign(a, invoke(o, a, a));
                        if (!equal(0, (n & 1)))
                                assign(*r, invoke(o, *r, a));
                        n >>= 1;
                }
                return *r;
        }
        return *r;
}

// vim:et:tabstop=8:shiftwidth=8:cindent:fo=croq:textwidth=80:

#endif // INSTIGATE_STL_POWER_HPP

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