SETBUSY
((struct header *)((char *)alloc_buf - minhead))->nextblk = SETBUSY(hd);
newend->nextblk = SETBUSY(&(arena[1]));
arenaend->nextblk = SETBUSY(newblk);
newend->nextblk = SETBUSY(&(arena[1]));
newend->nextblk = SETBUSY(&(arena[1]));
blk->nextblk = SETBUSY(newblk);
blk->nextblk = SETBUSY(blk->nextblk);
blk->nextblk = SETBUSY(next);
blk->nextblk = SETBUSY(next);
blk->nextblk = SETBUSY(newblk);