Optimization: reduce len() calls in add_polynomialcoeff

[hwwhww]

Description

I made some profiles on the DAS test case test_verify_cell_proof, which includes a compute_cells_and_proofs call and two verify_cell_proof calls. It turns out len() is somewhat expensive if we call it 400M times.

For the sake of tidiness and readability, We intentionally didn't have such optimization in spec writing. However, this one seems gain great performance improvement with only two extra lines.

Before

• Speed: in 356.67s (0:05:56)

After reducing the len() calls in add_polynomialcoeff

This minor optimization here use temporary variables to keep the len(a) and len(b) results:

def add_polynomialcoeff(a: PolynomialCoeff, b: PolynomialCoeff) -> PolynomialCoeff:
    """
    Sum the coefficient form polynomials ``a`` and ``b``.
    """
    a, b = (a, b) if len(a) >= len(b) else (b, a)
    length_a = len(a)
    length_b = len(b)
    return [(a[i] + (b[i] if i < length_b else 0)) % BLS_MODULUS for i in range(length_a)]

• Speed: in 234.21s (0:03:54)

It reduced ~35% time of this case.

[asn-d6]

LGTM!