fmt_str(b->ref, &s); kputc('\t', &s);
fmt_str(b->alt, &s); kputc('\t', &s);
kputw(b->qual, &s); kputc('\t', &s);
+ fmt_str(b->flt, &s); kputc('\t', &s);
fmt_str(b->info, &s); kputc('\t', &s);
fmt_str(b->fmt, &s);
x = b->n_alleles * (b->n_alleles + 1) / 2;