rp = &r.buf[len(r.buf)-1]
		} else {
			rp.n++
		}
	}
	return len(p), nil
}

func memset(a []byte, b byte) {
	if len(a) == 0 {
		return
	}
	// Double, until we reach power of 2 >= len(a), same as bytes.Repeat,
	// but without allocation.
	a[0] = b
	for i, l := 1, len(a); i < l; i *= 2 {
		copy(a[i:], a[:i])
	}
}