Multiplying two UINT256 to a UINT512

[Th0rgal]

Hello,

I need to compute a multiplication of two integers a, b modulo a big prime P. Those integers and the prime fit in a UINT256, but to compute the result of a*b mod P I need to compute a*b which doesn't fit in a UINT256. Would it be possible to add another method perfect_mul (or another name) which gives the UINT512 result in an efficient way or should I use UINT512 everywhere?

Thanks for your work,
Thomas

[ordian]

Hey, sorry for the delay in reply. Take a look at

parity-common/primitive-types/src/lib.rs

Lines 153 to 160 in 854e68b

	impl U256 {
	/// Multiplies two 256-bit integers to produce full 512-bit integer.
	/// Overflow is not possible.
	#[inline(always)]
	pub fn full_mul(self, other: U256) -> U512 {
	U512(uint_full_mul_reg!(U256, 4, self, other))
	}
	}

Hope that helps.