if (buf->tid < buf->head->b.core.tid) { // come to a new reference sequence
buf->tid = buf->head->b.core.tid; buf->pos = buf->head->beg; // jump to the next reference
} else if (buf->pos < buf->head->beg) { // here: tid == head->b.core.tid
if (buf->tid < buf->head->b.core.tid) { // come to a new reference sequence
buf->tid = buf->head->b.core.tid; buf->pos = buf->head->beg; // jump to the next reference
} else if (buf->pos < buf->head->beg) { // here: tid == head->b.core.tid