gcd_lcm.h

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#ifndef GUL14_GCD_LCM_H_
#define GUL14_GCD_LCM_H_
 
#include <type_traits>
#include "gul14/internal.h"
#include "gul14/num_util.h"
 
namespace gul14 {
 
template <typename IntTypeA, typename IntTypeB>
constexpr inline auto
gcd(IntTypeA a, IntTypeB b)
{
    static_assert(std::is_integral<IntTypeA>::value and std::is_integral<IntTypeB>::value,
        "gcd() arguments must be integers");
 
    static_assert(std::is_signed<IntTypeA>::value == std::is_signed<IntTypeB>::value,
        "gcd() arguments must have the same signedness");
 
    using CommonType = std::common_type_t<IntTypeA, IntTypeB>;
 
    auto c = gul14::abs(static_cast<CommonType>(a));
    auto d = gul14::abs(static_cast<CommonType>(b));
 
    while (d != 0)
    {
        CommonType tmp = d;
        d = c % d;
        c = tmp;
    }
 
    return c;
}
 
template <typename IntTypeA, typename IntTypeB>
constexpr inline auto
lcm(IntTypeA a, IntTypeB b)
{
    static_assert(std::is_integral<IntTypeA>::value and std::is_integral<IntTypeB>::value,
        "lcm() arguments must be integers");
 
    static_assert(std::is_signed<IntTypeA>::value == std::is_signed<IntTypeB>::value,
        "lcm() arguments must have the same signedness");
 
    using CommonType = std::common_type_t<IntTypeA, IntTypeB>;
 
    if (a == 0 && b == 0)
        return CommonType{ 0 };
 
    return static_cast<CommonType>(gul14::abs((a / gcd(a, b)) * b));
}
 
} // namespace gul14
 
#endif