_ls[_len] = l;
_xs[_len] = x;
if(_id  != null)_id[_len] = _len2;
_len++;
}
<BUG>_len2++;
}</BUG>
private void append2slowd() {
if( _len > Vec.CHUNK_SZ )
throw new ArrayIndexOutOfBoundsException(_len);

_ls[_len] = l;
_xs[_len] = x;
if(_id  != null)_id[_len] = _len2;
_len++;
}
_len2++;
assert _len <= _len2;
}
private void append2slowd() {
if( _len > Vec.CHUNK_SZ )
throw new ArrayIndexOutOfBoundsException(_len);
