Function bit_serial_add 

pub fn bit_serial_add(
    df: &mut DramDataflow,
    a: &[usize],
    b: &[usize],
    carry0: usize,
) -> Vec<usize>

Bit-serial ripple-carry ADD over B bitplanes (SIMD across the lanes packed in each row): for each bit i, sum_i = a_i XOR b_i XOR carry, carry = MAJ(a_i, b_i, carry). a/b are the operand-plane row indices (LSB first); carry0 is a zero row. Returns the B sum-plane rows. Composed entirely from the {AND, OR, NOT} basis — arithmetic emerging from boolean dataflow.