This is mostly glue code, with only a few instructions in ARM wired up
(PMUL but not PMULL), and no fallback code.
I would reword this to define what this operation does, then add a remark about how it's different from integer multiplication. Something like:
"In the scalar version with operands of type iN, both operands are assumed to be polynomials with binary coefficients, where the most significant bit corresponds to the coefficient at x^(N-1). The operation calculates the result of polynomial multiplication of the operands, modulo x^N.
Note that this is different from integer multiplication ..."