HAMMER2_BMAP_INDEX_MASK
((((int)data_off & HAMMER2_BMAP_INDEX_MASK) >>
j = (sub_key & HAMMER2_BMAP_INDEX_MASK) /
((((int)data_off & HAMMER2_BMAP_INDEX_MASK) >>
j = (sub_key & HAMMER2_BMAP_INDEX_MASK) /