at_bslend
if (apt.at_bslst == 0 || apt.at_bslend == 0) {
apt.at_bslst = apt.at_bslend = 0;
if (p1->ap_st >= apt.at_bslst && p1->ap_st <= apt.at_bslend)
apt->at_bslend = root->ar_bslst + root->ar_bslsize - 1;