Bignum Math

Bignum Math is a library for performing arithmetic operations on large numbers.

How might you accomplish this using bmi2 & adx?

From Martins Mozeiko

Without simd best you can do is bmi2 and adx. That's how fastest x25519 curve implementations are done here and here

It does a bit more, because it needs to reduce result by curve modulo. it needs to calculate (a * b) % p, not just a*b

That article is about their s2n-bignum library