if (PR_UPTRDIFF(mark, a) < PR_UPTRDIFF(a->avail, a)) {
if (PR_UPTRDIFF(mark, a->base) < PR_UPTRDIFF(a->avail, a->base)) {
PR_IMPLEMENT(void) PL_ArenaRelease(PLArenaPool *pool, char *mark){    PLArena *a;    for (a = pool->first.next; a; a = a->next) {        if (PR_UPTRDIFF(mark, a) < PR_UPTRDIFF(a->avail, a)) {            a->avail = (PRUword)PL_ARENA_ALIGN(pool, mark);            FreeArenaList(pool, a, PR_TRUE);            return;        }    }}