src/pkg/exp/regexp/exec.go - go - Git at Google

 package regexp

 import "exp/regexp/syntax"

 // A queue is a 'sparse array' holding pending threads of execution.
 // See http://research.swtch.com/2008/03/using-uninitialized-memory-for-fun-and.html
 type queue struct {
 	sparse []uint32
 	dense  []entry
 }

 // A entry is an entry on a queue.
 // It holds both the instruction pc and the actual thread.
 // Some queue entries are just place holders so that the machine
 // knows it has considered that pc.  Such entries have t == nil.
 type entry struct {
 	pc uint32
 	t  *thread
 }

 // A thread is the state of a single path through the machine:
 // an instruction and a corresponding capture array.
 // See http://swtch.com/~rsc/regexp/regexp2.html
 type thread struct {
 	inst *syntax.Inst
 	cap  []int
 }

 // A machine holds all the state during an NFA simulation for p.
 type machine struct {
 	re       *Regexp      // corresponding Regexp
 	p        *syntax.Prog // compiled program
 	q0, q1   queue        // two queues for runq, nextq
 	pool     []*thread    // pool of available threads
 	matched  bool         // whether a match was found
 	matchcap []int        // capture information for the match
 }

 // progMachine returns a new machine running the prog p.
 func progMachine(p *syntax.Prog) *machine {
 	m := &machine{p: p}
 	n := len(m.p.Inst)
 	m.q0 = queue{make([]uint32, n), make([]entry, 0, n)}
 	m.q1 = queue{make([]uint32, n), make([]entry, 0, n)}
 	ncap := p.NumCap
 	if ncap < 2 {
 		ncap = 2
 	}
 	m.matchcap = make([]int, ncap)
 	return m
 }

 // alloc allocates a new thread with the given instruction.
 // It uses the free pool if possible.
 func (m *machine) alloc(i *syntax.Inst) *thread {
 	var t *thread
 	if n := len(m.pool); n > 0 {
 		t = m.pool[n-1]
 		m.pool = m.pool[:n-1]
 	} else {
 		t = new(thread)
 		t.cap = make([]int, cap(m.matchcap))
 	}
 	t.cap = t.cap[:len(m.matchcap)]
 	t.inst = i
 	return t
 }

 // free returns t to the free pool.
 func (m *machine) free(t *thread) {
 	m.pool = append(m.pool, t)
 }

 // match runs the machine over the input starting at pos.
 // It reports whether a match was found.
 // If so, m.matchcap holds the submatch information.
 func (m *machine) match(i input, pos int) bool {
 	startCond := m.re.cond
 	if startCond == ^syntax.EmptyOp(0) { // impossible
 		return false
 	}
 	m.matched = false
 	for i := range m.matchcap {
 		m.matchcap[i] = -1
 	}
 	runq, nextq := &m.q0, &m.q1
 	rune, rune1 := endOfText, endOfText
 	width, width1 := 0, 0
 	rune, width = i.step(pos)
 	if rune != endOfText {
 		rune1, width1 = i.step(pos + width)
 	}
 	// TODO: Let caller specify the initial flag setting.
 	// For now assume pos == 0 is beginning of text and
 	// pos != 0 is not even beginning of line.
 	// TODO: Word boundary.
 	var flag syntax.EmptyOp
 	if pos == 0 {
 		flag = syntax.EmptyBeginText | syntax.EmptyBeginLine
 	}

 	// Update flag using lookahead rune.
 	if rune1 == '\n' {
 		flag |= syntax.EmptyEndLine
 	}
 	if rune1 == endOfText {
 		flag |= syntax.EmptyEndText
 	}

 	for {
 		if len(runq.dense) == 0 {
 			if startCond&syntax.EmptyBeginText != 0 && pos != 0 {
 				// Anchored match, past beginning of text.
 				break
 			}
 			if m.matched {
 				// Have match; finished exploring alternatives.
 				break
 			}
 			if len(m.re.prefix) > 0 && rune1 != m.re.prefixRune && i.canCheckPrefix() {
 				// Match requires literal prefix; fast search for it.
 				advance := i.index(m.re, pos)
 				if advance < 0 {
 					break
 				}
 				pos += advance
 				rune, width = i.step(pos)
 				rune1, width1 = i.step(pos + width)
 			}
 		}
 		if !m.matched {
 			if len(m.matchcap) > 0 {
 				m.matchcap[0] = pos
 			}
 			m.add(runq, uint32(m.p.Start), pos, m.matchcap, flag)
 		}
 		// TODO: word boundary
 		flag = 0
 		if rune == '\n' {
 			flag |= syntax.EmptyBeginLine
 		}
 		if rune1 == '\n' {
 			flag |= syntax.EmptyEndLine
 		}
 		if rune1 == endOfText {
 			flag |= syntax.EmptyEndText
 		}
 		m.step(runq, nextq, pos, pos+width, rune, flag)
 		if width == 0 {
 			break
 		}
 		pos += width
 		rune, width = rune1, width1
 		if rune != endOfText {
 			rune1, width1 = i.step(pos + width)
 		}
 		runq, nextq = nextq, runq
 	}
 	m.clear(nextq)
 	return m.matched
 }

 // clear frees all threads on the thread queue.
 func (m *machine) clear(q *queue) {
 	for _, d := range q.dense {
 		if d.t != nil {
 			m.free(d.t)
 		}
 	}
 	q.dense = q.dense[:0]
 }

 // step executes one step of the machine, running each of the threads
 // on runq and appending new threads to nextq.
 // The step processes the rune c (which may be endOfText),
 // which starts at position pos and ends at nextPos.
 // nextCond gives the setting for the empty-width flags after c.
 func (m *machine) step(runq, nextq *queue, pos, nextPos, c int, nextCond syntax.EmptyOp) {
 	for j := 0; j < len(runq.dense); j++ {
 		d := &runq.dense[j]
 		t := d.t
 		if t == nil {
 			continue
 		}
 		/*
 			 * If we support leftmost-longest matching:
 				if longest && matched && match[0] < t.cap[0] {
 					m.free(t)
 					continue
 				}
 		*/

 		i := t.inst
 		switch i.Op {
 		default:
 			panic("bad inst")

 		case syntax.InstMatch:
 			if len(t.cap) > 0 {
 				t.cap[1] = pos
 				copy(m.matchcap, t.cap)
 			}
 			m.matched = true
 			for _, d := range runq.dense[j+1:] {
 				if d.t != nil {
 					m.free(d.t)
 				}
 			}
 			runq.dense = runq.dense[:0]

 		case syntax.InstRune:
 			if i.MatchRune(c) {
 				m.add(nextq, i.Out, nextPos, t.cap, nextCond)
 			}
 		}
 		m.free(t)
 	}
 	runq.dense = runq.dense[:0]
 }

 // add adds an entry to q for pc, unless the q already has such an entry.
 // It also recursively adds an entry for all instructions reachable from pc by following
 // empty-width conditions satisfied by cond.  pos gives the current position
 // in the input.
 func (m *machine) add(q *queue, pc uint32, pos int, cap []int, cond syntax.EmptyOp) {
 	if pc == 0 {
 		return
 	}
 	if j := q.sparse[pc]; j < uint32(len(q.dense)) && q.dense[j].pc == pc {
 		return
 	}

 	j := len(q.dense)
 	q.dense = q.dense[:j+1]
 	d := &q.dense[j]
 	d.t = nil
 	d.pc = pc
 	q.sparse[pc] = uint32(j)

 	i := &m.p.Inst[pc]
 	switch i.Op {
 	default:
 		panic("unhandled")
 	case syntax.InstFail:
 		// nothing
 	case syntax.InstAlt, syntax.InstAltMatch:
 		m.add(q, i.Out, pos, cap, cond)
 		m.add(q, i.Arg, pos, cap, cond)
 	case syntax.InstEmptyWidth:
 		if syntax.EmptyOp(i.Arg)&^cond == 0 {
 			m.add(q, i.Out, pos, cap, cond)
 		}
 	case syntax.InstNop:
 		m.add(q, i.Out, pos, cap, cond)
 	case syntax.InstCapture:
 		if int(i.Arg) < len(cap) {
 			opos := cap[i.Arg]
 			cap[i.Arg] = pos
 			m.add(q, i.Out, pos, cap, cond)
 			cap[i.Arg] = opos
 		} else {
 			m.add(q, i.Out, pos, cap, cond)
 		}
 	case syntax.InstMatch, syntax.InstRune:
 		t := m.alloc(i)
 		if len(t.cap) > 0 {
 			copy(t.cap, cap)
 		}
 		d.t = t
 	}
 }

 // empty is a non-nil 0-element slice,
 // so doExecute can avoid an allocation
 // when 0 captures are requested from a successful match.
 var empty = make([]int, 0)

 // doExecute finds the leftmost match in the input and returns
 // the position of its subexpressions.
 func (re *Regexp) doExecute(i input, pos int, ncap int) []int {
 	m := re.get()
 	m.matchcap = m.matchcap[:ncap]
 	if !m.match(i, pos) {
 		re.put(m)
 		return nil
 	}
 	if ncap == 0 {
 		re.put(m)
 		return empty // empty but not nil
 	}
 	cap := make([]int, ncap)
 	copy(cap, m.matchcap)
 	re.put(m)
 	return cap
 }
	package regexp

	import "exp/regexp/syntax"

	// A queue is a 'sparse array' holding pending threads of execution.
	// See http://research.swtch.com/2008/03/using-uninitialized-memory-for-fun-and.html
	type queue struct {
	sparse []uint32
	dense []entry
	}

	// A entry is an entry on a queue.
	// It holds both the instruction pc and the actual thread.
	// Some queue entries are just place holders so that the machine
	// knows it has considered that pc. Such entries have t == nil.
	type entry struct {
	pc uint32
	t *thread
	}

	// A thread is the state of a single path through the machine:
	// an instruction and a corresponding capture array.
	// See http://swtch.com/~rsc/regexp/regexp2.html
	type thread struct {
	inst *syntax.Inst
	cap []int
	}

	// A machine holds all the state during an NFA simulation for p.
	type machine struct {
	re *Regexp // corresponding Regexp
	p *syntax.Prog // compiled program
	q0, q1 queue // two queues for runq, nextq
	pool []*thread // pool of available threads
	matched bool // whether a match was found
	matchcap []int // capture information for the match
	}

	// progMachine returns a new machine running the prog p.
	func progMachine(p syntax.Prog) machine {
	m := &machine{p: p}
	n := len(m.p.Inst)
	m.q0 = queue{make([]uint32, n), make([]entry, 0, n)}
	m.q1 = queue{make([]uint32, n), make([]entry, 0, n)}
	ncap := p.NumCap
	if ncap < 2 {
	ncap = 2
	}
	m.matchcap = make([]int, ncap)
	return m
	}

	// alloc allocates a new thread with the given instruction.
	// It uses the free pool if possible.
	func (m machine) alloc(i syntax.Inst) *thread {
	var t *thread
	if n := len(m.pool); n > 0 {
	t = m.pool[n-1]
	m.pool = m.pool[:n-1]
	} else {
	t = new(thread)
	t.cap = make([]int, cap(m.matchcap))
	}
	t.cap = t.cap[:len(m.matchcap)]
	t.inst = i
	return t
	}

	// free returns t to the free pool.
	func (m machine) free(t thread) {
	m.pool = append(m.pool, t)
	}

	// match runs the machine over the input starting at pos.
	// It reports whether a match was found.
	// If so, m.matchcap holds the submatch information.
	func (m *machine) match(i input, pos int) bool {
	startCond := m.re.cond
	if startCond == ^syntax.EmptyOp(0) { // impossible
	return false
	}
	m.matched = false
	for i := range m.matchcap {
	m.matchcap[i] = -1
	}
	runq, nextq := &m.q0, &m.q1
	rune, rune1 := endOfText, endOfText
	width, width1 := 0, 0
	rune, width = i.step(pos)
	if rune != endOfText {
	rune1, width1 = i.step(pos + width)
	}
	// TODO: Let caller specify the initial flag setting.
	// For now assume pos == 0 is beginning of text and
	// pos != 0 is not even beginning of line.
	// TODO: Word boundary.
	var flag syntax.EmptyOp
	if pos == 0 {
	flag = syntax.EmptyBeginText \| syntax.EmptyBeginLine
	}

	// Update flag using lookahead rune.
	if rune1 == '\n' {
	flag \|= syntax.EmptyEndLine
	}
	if rune1 == endOfText {
	flag \|= syntax.EmptyEndText
	}

	for {
	if len(runq.dense) == 0 {
	if startCond&syntax.EmptyBeginText != 0 && pos != 0 {
	// Anchored match, past beginning of text.
	break
	}
	if m.matched {
	// Have match; finished exploring alternatives.
	break
	}
	if len(m.re.prefix) > 0 && rune1 != m.re.prefixRune && i.canCheckPrefix() {
	// Match requires literal prefix; fast search for it.
	advance := i.index(m.re, pos)
	if advance < 0 {
	break
	}
	pos += advance
	rune, width = i.step(pos)
	rune1, width1 = i.step(pos + width)
	}
	}
	if !m.matched {
	if len(m.matchcap) > 0 {
	m.matchcap[0] = pos
	}
	m.add(runq, uint32(m.p.Start), pos, m.matchcap, flag)
	}
	// TODO: word boundary
	flag = 0
	if rune == '\n' {
	flag \|= syntax.EmptyBeginLine
	}
	if rune1 == '\n' {
	flag \|= syntax.EmptyEndLine
	}
	if rune1 == endOfText {
	flag \|= syntax.EmptyEndText
	}
	m.step(runq, nextq, pos, pos+width, rune, flag)
	if width == 0 {
	break
	}
	pos += width
	rune, width = rune1, width1
	if rune != endOfText {
	rune1, width1 = i.step(pos + width)
	}
	runq, nextq = nextq, runq
	}
	m.clear(nextq)
	return m.matched
	}

	// clear frees all threads on the thread queue.
	func (m machine) clear(q queue) {
	for _, d := range q.dense {
	if d.t != nil {
	m.free(d.t)
	}
	}
	q.dense = q.dense[:0]
	}

	// step executes one step of the machine, running each of the threads
	// on runq and appending new threads to nextq.
	// The step processes the rune c (which may be endOfText),
	// which starts at position pos and ends at nextPos.
	// nextCond gives the setting for the empty-width flags after c.
	func (m machine) step(runq, nextq queue, pos, nextPos, c int, nextCond syntax.EmptyOp) {
	for j := 0; j < len(runq.dense); j++ {
	d := &runq.dense[j]
	t := d.t
	if t == nil {
	continue
	}
	/*
	* If we support leftmost-longest matching:
	if longest && matched && match[0] < t.cap[0] {
	m.free(t)
	continue
	}
	*/

	i := t.inst
	switch i.Op {
	default:
	panic("bad inst")

	case syntax.InstMatch:
	if len(t.cap) > 0 {
	t.cap[1] = pos
	copy(m.matchcap, t.cap)
	}
	m.matched = true
	for _, d := range runq.dense[j+1:] {
	if d.t != nil {
	m.free(d.t)
	}
	}
	runq.dense = runq.dense[:0]

	case syntax.InstRune:
	if i.MatchRune(c) {
	m.add(nextq, i.Out, nextPos, t.cap, nextCond)
	}
	}
	m.free(t)
	}
	runq.dense = runq.dense[:0]
	}

	// add adds an entry to q for pc, unless the q already has such an entry.
	// It also recursively adds an entry for all instructions reachable from pc by following
	// empty-width conditions satisfied by cond. pos gives the current position
	// in the input.
	func (m machine) add(q queue, pc uint32, pos int, cap []int, cond syntax.EmptyOp) {
	if pc == 0 {
	return
	}
	if j := q.sparse[pc]; j < uint32(len(q.dense)) && q.dense[j].pc == pc {
	return
	}

	j := len(q.dense)
	q.dense = q.dense[:j+1]
	d := &q.dense[j]
	d.t = nil
	d.pc = pc
	q.sparse[pc] = uint32(j)

	i := &m.p.Inst[pc]
	switch i.Op {
	default:
	panic("unhandled")
	case syntax.InstFail:
	// nothing
	case syntax.InstAlt, syntax.InstAltMatch:
	m.add(q, i.Out, pos, cap, cond)
	m.add(q, i.Arg, pos, cap, cond)
	case syntax.InstEmptyWidth:
	if syntax.EmptyOp(i.Arg)&^cond == 0 {
	m.add(q, i.Out, pos, cap, cond)
	}
	case syntax.InstNop:
	m.add(q, i.Out, pos, cap, cond)
	case syntax.InstCapture:
	if int(i.Arg) < len(cap) {
	opos := cap[i.Arg]
	cap[i.Arg] = pos
	m.add(q, i.Out, pos, cap, cond)
	cap[i.Arg] = opos
	} else {
	m.add(q, i.Out, pos, cap, cond)
	}
	case syntax.InstMatch, syntax.InstRune:
	t := m.alloc(i)
	if len(t.cap) > 0 {
	copy(t.cap, cap)
	}
	d.t = t
	}
	}

	// empty is a non-nil 0-element slice,
	// so doExecute can avoid an allocation
	// when 0 captures are requested from a successful match.
	var empty = make([]int, 0)

	// doExecute finds the leftmost match in the input and returns
	// the position of its subexpressions.
	func (re *Regexp) doExecute(i input, pos int, ncap int) []int {
	m := re.get()
	m.matchcap = m.matchcap[:ncap]
	if !m.match(i, pos) {
	re.put(m)
	return nil
	}
	if ncap == 0 {
	re.put(m)
	return empty // empty but not nil
	}
	cap := make([]int, ncap)
	copy(cap, m.matchcap)
	re.put(m)
	return cap
	}