Wrong calculation of actual_sum in univariate sumcheck

[tsunrise]

libiop/libiop/protocols/encoded/sumcheck/sumcheck.tcc

Lines 367 to 381 in a2ed2ec

	#ifdef DEBUG
	polynomial<FieldT> g = h_and_g.second;
	FieldT actual_sum;
	if (this->field_subset_type_ == affine_subspace_type) {
	/* The second component is actually g + sum * x^{H_size-1}, but
	we immediately remove its highest degree term */
	actual_sum = g[this->summation_domain_size_-1];
	g.set_degree(this->summation_domain_size_-2, true);
	} else if (this->field_subset_type_ == multiplicative_coset_type) {
	/* The second component is actually x*g + sum, but
	we immediately remove its lowest degree term */
	actual_sum = g[0];
	g.remove_term(0);
	}
	#endif // DEBUG

Here, actual_sum should be g[0] * this->summation_domain_size instead of g[0].
Please see https://github.com/arkworks-rs/bcs/blob/2ddd1db3838cbf393a8d8d7eafe6a004aa584c61/sumcheck/src/util.rs#L16-L27 for a possible fix