static_gcd.h

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/*
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      names of its contributors may be used to endorse or promote products
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*/
 
#pragma once
namespace trove {
 
template<int u, int v>
struct static_gcd;
 
namespace detail {
 
template<bool u_odd, bool v_odd, int u, int v>
struct static_gcd_helper {
    static const int value = static_gcd<(u>>1), (v>>1)>::value << 1;
};
 
template<int u, int v>
struct static_gcd_helper<false, true, u, v> {
    static const int value = static_gcd<(u>>1), v>::value;
};
 
template<int u, int v>
struct static_gcd_helper<true, false, u, v> {
    static const int value = static_gcd<u, (v>>1)>::value;
};
 
template<int u, int v>
struct static_gcd_helper<true, true, u, v> {
    static const int reduced_u = (u > v) ? ((u - v) >> 1) : ((v - u) >> 1);
    static const int reduced_v = (u > v) ? v : u;
    static const int value = static_gcd<reduced_u, reduced_v>::value;
};
}
 
template<int u, int v>
struct static_gcd {
    static const bool u_odd = (u & 0x1) == 1;
    static const bool v_odd = (v & 0x1) == 1;
    static const bool equal = u == v;
    static const int value = equal ? u : detail::static_gcd_helper<u_odd, v_odd, u, v>::value;
};
 
template<int v>
struct static_gcd<0, v> {
    static const bool value = v;
};
 
template<int u>
struct static_gcd<u, 0> {
    static const bool value = u;
};
 
}