Function eq_ind_truncate_low_inplace

pub fn eq_ind_truncate_low_inplace<P: PackedField, Data: DerefMut<Target = [P]>>(
    values: &mut FieldBuffer<P, Data>,
    truncated_log_len: usize,
) -> Result<(), Error>

Truncate the equality indicator expansion to the low indexed variables.

This routine computes $\widetilde{eq}(X_0, …, X_{n’-1}, r_0, …, r_{n’-1})$ from $\widetilde{eq}(X_0, …, X_{n-1}, r_0, …, r_{n-1})$ where $n’ \le n$ by repeatedly summing field buffer “halves” inplace. The equality indicator expansion occupies a prefix of the field buffer; scalars after the truncated length are zeroed out.