Change Details

Use a `union` to store the result and `memcpy()` it to the `uint256` lower 64 bits. Using `arith_uint256` would be more straightforward but it requires a conversion that has a measurable impact on the benchmark performance. This does not change the behavior.

Use a `union` to directly store the result and read from it. The `memcpy` is only added for strict standard compliance, and should be optimized out by the compiler. Note that this works because the `uin256_t` `WIDTH` member is a `constexpr`. This does not change the behavior.

Use a `union` to directly store the result and `memcpy()` it to the `uint256`read from it. lower 64 bits.The `memcpy` is only added for strict standard compliance, Using `arith_uint256` would be more straightforward but it requires aand should be optimized out by the compiler. Note that this works because the `uin256_t` `WIDTH` member conversion that has a measurable impact on the benchmark performanceis a `constexpr`. This does not change the behavior.