Faster computation of binomial product

[mforets]

From Section 3.1 in [S09], about computing the coefficients for univariate monomials,

This computation can be simplified by observing that the part of the formula consisting of the two binomial coefficients where m appears can always be expressed as a product of k factors.

[S09] Smith, A. P. (2009). Fast construction of constant bound functions for sparse polynomials. Journal of Global Optimization, 43(2-3), 445-458.

[TP96] Trump, W., & Prautzsch, H. (1996). Arbitrarily high degree elevation of Bézier representations. Computer Aided Geometric Design, 13(5), 387-398.