is_head = 1;
if (c->n_cigar == 1) { // just one operation, save a loop
if (_cop(cigar[0]) == BAM_CMATCH) s->k = 0, s->x = c->pos, s->y = 0;
is_head = 1;
if (c->n_cigar == 1) { // just one operation, save a loop
if (_cop(cigar[0]) == BAM_CMATCH) s->k = 0, s->x = c->pos, s->y = 0;