// stepByte steps runq to nextq consuming c and then expanding according to flag.
// It returns true if a match ends immediately before c.
// c is either an input byte or endText.
func (m *matcher) stepByte(runq, nextq *sparse.Set, c int, flag syntax.EmptyOp) (match bool) {
	nextq.Reset()
	m.addq(nextq, uint32(m.prog.Start), flag)
	for _, id := range runq.Dense() {
		i := &m.prog.Inst[id]
		switch i.Op {
		default:
			continue
		case syntax.InstMatch:
			match = true
			continue
		case instByteRange:
			if c == endText {
				break
			}
			lo := int((i.Arg >> 8) & 0xFF)
			hi := int(i.Arg & 0xFF)
			ch := c
			if i.Arg&argFold != 0 && 'a' <= ch && ch <= 'z' {
				ch += 'A' - 'a'
			}
			if lo <= ch && ch <= hi {
				m.addq(nextq, i.Out, flag)
			}
		}
	}
	return
}

// addq adds id to the queue, expanding according to flag.
func (m *matcher) addq(q *sparse.Set, id uint32, flag syntax.EmptyOp) {
	if q.Has(id) {
		return
	}
	q.Add(id)
	i := &m.prog.Inst[id]
	switch i.Op {
	case syntax.InstCapture, syntax.InstNop:
		m.addq(q, i.Out, flag)
	case syntax.InstAlt, syntax.InstAltMatch:
		m.addq(q, i.Out, flag)
		m.addq(q, i.Arg, flag)
	case syntax.InstEmptyWidth:
		if syntax.EmptyOp(i.Arg)&^flag == 0 {
			m.addq(q, i.Out, flag)
		}
	}
}

// stepEmpty steps runq to nextq expanding according to flag.
func (m *matcher) stepEmpty(runq, nextq *sparse.Set, flag syntax.EmptyOp) {
	nextq.Reset()
	for _, id := range runq.Dense() {
		m.addq(nextq, id, flag)
	}
}