Residue number systems are really neat! They're sometimes used in crypto implementations, but there you're doing modular multiplication and in most cases the modular reduction then becomes costly, so it's not a free lunch. (Except in RSA and a few other cases. RSA-CRT gets you a "free" ~4x performance boost except it's more brittle to mistakes and side-channel / fault attacks.)
There's also NTT / Fourier multiplication as an option, for big integers or polynomials or modular arithmetic.
There's also NTT / Fourier multiplication as an option, for big integers or polynomials or modular arithmetic.