J. Symb. Comp. 44 (2009), 1502–1510 (DOI).
arXiv preprint (December 2007) (published version is substantially revised and improved).
We present several new algorithms for dense polynomial multiplication in Z[x] based on the Kronecker substitution method. Instead of reducing to a single integer multiplication, we reduce to several smaller multiplications. We describe an implementation of multiplication in (Z/nZ)[x] for a word-sized modulus n based on these methods, and compare its performance to that of NTL and Magma.
See the file mul_ks.c in zn_poly.