sack_blk_clr
sf->sf_bits = sack_blk_clr(sf, i);
sf->sf_bits = sack_blk_clr(sf, idx);
sf->sf_bits = sack_blk_clr(sf, src);
sf->sf_bits = sack_blk_clr(sf, i);
sf->sf_bits = sack_blk_clr(sf, i);