TESTBUSY
if (TESTBUSY(blk->nextblk) == 0) {
if (!TESTBUSY(nextnext = next->nextblk)) {
} while (!TESTBUSY(nextnext));
} else if (TESTBUSY(lastblk->nextblk)) {
if (!TESTBUSY(holdblk))
if (!TESTBUSY(next))
if (!TESTBUSY(nextnext = next->nextblk)) {
} while (!TESTBUSY(nextnext = next->nextblk));
if (!TESTBUSY(next)) {
if (!TESTBUSY(next->nextblk)) {
} while (!TESTBUSY(next->nextblk));
if (TESTBUSY(blk->nextblk)) {