if (isPaired) {
assert(samread(in, b2) >= 0 && (b2->core.flag & 0x0001));
assert((b->core.flag & 0x0001) && (b2->core.flag & 0x0001));
if (isPaired) {
assert(samread(in, b2) >= 0 && (b2->core.flag & 0x0001));
assert((b->core.flag & 0x0001) && (b2->core.flag & 0x0001));