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ratio_type_constexpr refactored to provide safe_multiply

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Mateusz Pusz
2019-05-18 21:21:46 +02:00
parent 7caadfcd0d
commit 6780978be6
1 changed files with 27 additions and 9 deletions
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36
test/metabench/ratio/ratio_type_constexpr.h
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@@ -25,6 +25,7 @@
#include <type_traits> #include <type_traits>
#include <numeric> #include <numeric>
#include <cstdint> #include <cstdint>
#include <gsl/gsl-lite.hpp>
namespace units { namespace units {
@@ -66,16 +67,33 @@ namespace units {
namespace detail { namespace detail {
static constexpr std::intmax_t safe_multiply(std::intmax_t lhs, std::intmax_t rhs)
{
constexpr std::uintmax_t c = std::uintmax_t(1) << (sizeof(std::intmax_t) * 4);
const std::uintmax_t a0 = detail::abs(lhs) % c;
const std::uintmax_t a1 = detail::abs(lhs) / c;
const std::uintmax_t b0 = detail::abs(rhs) % c;
const std::uintmax_t b1 = detail::abs(rhs) / c;
Expects(a1 == 0 || b1 == 0); // overflow in multiplication
Expects(a0 * b1 + b0 * a1 < (c >> 1)); // overflow in multiplication
Expects(b0 * a0 <= INTMAX_MAX); // overflow in multiplication
Expects((a0 * b1 + b0 * a1) * c <= INTMAX_MAX - b0 * a0); // overflow in multiplication
return lhs * rhs;
}
template<typename R1, typename R2> template<typename R1, typename R2>
struct ratio_multiply { struct ratio_multiply {
private: private:
static constexpr intmax_t gcd1 = std::gcd(R1::num, R2::den); static constexpr std::intmax_t gcd1 = std::gcd(R1::num, R2::den);
static constexpr intmax_t gcd2 = std::gcd(R2::num, R1::den); static constexpr std::intmax_t gcd2 = std::gcd(R2::num, R1::den);
public: public:
using type = ratio<(R1::num / gcd1) * (R2::num / gcd2), (R1::den / gcd2) * (R2::den / gcd1)>; using type = ratio<safe_multiply(R1::num / gcd1, R2::num / gcd2), safe_multiply(R1::den / gcd2, R2::den / gcd1)>;
static constexpr intmax_t num = type::num; static constexpr std::intmax_t num = type::num;
static constexpr intmax_t den = type::den; static constexpr std::intmax_t den = type::den;
}; };
} }
@@ -91,8 +109,8 @@ namespace units {
struct ratio_divide { struct ratio_divide {
static_assert(R2::num != 0, "division by 0"); static_assert(R2::num != 0, "division by 0");
using type = ratio_multiply<R1, ratio<R2::den, R2::num>>; using type = ratio_multiply<R1, ratio<R2::den, R2::num>>;
static constexpr intmax_t num = type::num; static constexpr std::intmax_t num = type::num;
static constexpr intmax_t den = type::den; static constexpr std::intmax_t den = type::den;
}; };
} }
@@ -105,8 +123,8 @@ namespace units {
// todo: simplified // todo: simplified
template<Ratio R1, Ratio R2> template<Ratio R1, Ratio R2>
struct common_ratio { struct common_ratio {
static constexpr intmax_t gcd_num = std::gcd(R1::num, R2::num); static constexpr std::intmax_t gcd_num = std::gcd(R1::num, R2::num);
static constexpr intmax_t gcd_den = std::gcd(R1::den, R2::den); static constexpr std::intmax_t gcd_den = std::gcd(R1::den, R2::den);
using type = ratio<gcd_num, (R1::den / gcd_den) * R2::den>; using type = ratio<gcd_num, (R1::den / gcd_den) * R2::den>;
}; };