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Merged
mborland merged 1 commit into from
Jul 24, 2026
Merged

Improve performance of widening muls #461

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15 changes: 14 additions & 1 deletion include/boost/int128/detail/int128_imp.hpp
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Original file line number Diff line number Diff line change
Expand Up @@ -2052,12 +2052,20 @@ namespace detail {

BOOST_INT128_HOST_DEVICE BOOST_INT128_FORCE_INLINE constexpr int128_t default_mul(const int128_t lhs, const std::uint64_t rhs) noexcept
{
#if defined(BOOST_INT128_HAS_INT128) && !defined(__s390__) && !defined(__s390x__)

return int128_t{static_cast<detail::builtin_u128>(lhs) * static_cast<detail::builtin_u128>(rhs)};

#else

return low_word_mul<int128_t>(lhs, rhs);

#endif
}

BOOST_INT128_HOST_DEVICE BOOST_INT128_FORCE_INLINE constexpr int128_t default_mul(const int128_t lhs, const std::uint32_t rhs) noexcept
{
return low_word_mul<int128_t>(lhs, rhs);
return default_mul(lhs, static_cast<std::uint64_t>(rhs));
}

#if defined(_M_AMD64) && !defined(__GNUC__)
Expand Down Expand Up @@ -2131,6 +2139,11 @@ BOOST_INT128_HOST_DEVICE BOOST_INT128_FORCE_INLINE constexpr int128_t default_mu
return msvc_amd64_mul(lhs, rhs);
}

#elif defined(BOOST_INT128_HAS_INT128) && !defined(__s390__) && !defined(__s390x__)

// Multiply in the unsigned domain to avoid signed-overflow UB, then reinterpret the bits.
return int128_t{static_cast<detail::builtin_u128>(lhs) * static_cast<detail::builtin_u128>(rhs)};

#else

return low_word_mul<int128_t>(lhs, rhs);
Expand Down
9 changes: 9 additions & 0 deletions include/boost/int128/detail/uint128_imp.hpp
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Original file line number Diff line number Diff line change
Expand Up @@ -1915,6 +1915,10 @@ BOOST_INT128_HOST_DEVICE BOOST_INT128_FORCE_INLINE constexpr uint128_t default_a

return res;

#elif (defined(__x86_64__) || (defined(__aarch64__) && !defined(__APPLE__))) && !defined(_MSC_VER) && defined(BOOST_INT128_HAS_INT128)

return static_cast<uint128_t>(static_cast<detail::builtin_u128>(lhs) + static_cast<detail::builtin_u128>(rhs));

#else

uint128_t temp {lhs.high + rhs.high, lhs.low + rhs.low};
Expand Down Expand Up @@ -2306,6 +2310,11 @@ BOOST_INT128_HOST_DEVICE BOOST_INT128_FORCE_INLINE constexpr uint128_t default_m
return msvc_mul(lhs, rhs);
}

#elif defined(BOOST_INT128_HAS_INT128) && !defined(__s390__) && !defined(__s390x__)
# define BOOST_INT128_HIDE_MUL

return static_cast<uint128_t>(static_cast<detail::builtin_u128>(lhs) * static_cast<detail::builtin_u128>(rhs));

#endif

// We need to hide this if we use a non-const eval method above to avoid a litany of cross-platform warnings
Expand Down
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