HAMMER_ENCODE
blockmap->alloc_offset = HAMMER_ENCODE(zone, 255, -1);
*offsetp = HAMMER_ENCODE(zone, vol_no, 0);
HAMMER_ENCODE(HAMMER_ZONE_RAW_VOLUME_INDEX, vol_no, offset)
HAMMER_ENCODE(HAMMER_ZONE_RAW_BUFFER_INDEX, vol_no, offset)
HAMMER_ENCODE(HAMMER_ZONE_UNDO_INDEX, HAMMER_ROOT_VOLNO, offset)
HAMMER_ENCODE(HAMMER_ZONE_FREEMAP_INDEX, vol_no, offset)
io1_offset = HAMMER_ENCODE(0, io1->volume->vol_no, io1->offset);
io2_offset = HAMMER_ENCODE(0, io2->volume->vol_no, io2->offset);