346 lines
8.3 KiB
Go
346 lines
8.3 KiB
Go
// Copyright 2011 The Go Authors. All rights reserved.
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// Use of this source code is governed by a BSD-style
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// license that can be found in the LICENSE file.
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package regexp
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import (
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"io"
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"regexp/syntax"
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)
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// A queue is a 'sparse array' holding pending threads of execution.
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// See http://research.swtch.com/2008/03/using-uninitialized-memory-for-fun-and.html
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type queue struct {
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sparse []uint32
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dense []entry
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}
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// A entry is an entry on a queue.
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// It holds both the instruction pc and the actual thread.
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// Some queue entries are just place holders so that the machine
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// knows it has considered that pc. Such entries have t == nil.
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type entry struct {
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pc uint32
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t *thread
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}
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// A thread is the state of a single path through the machine:
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// an instruction and a corresponding capture array.
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// See http://swtch.com/~rsc/regexp/regexp2.html
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type thread struct {
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inst *syntax.Inst
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cap []int
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}
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// A machine holds all the state during an NFA simulation for p.
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type machine struct {
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re *Regexp // corresponding Regexp
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p *syntax.Prog // compiled program
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q0, q1 queue // two queues for runq, nextq
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pool []*thread // pool of available threads
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matched bool // whether a match was found
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matchcap []int // capture information for the match
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// cached inputs, to avoid allocation
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inputBytes inputBytes
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inputString inputString
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inputReader inputReader
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}
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func (m *machine) newInputBytes(b []byte) input {
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m.inputBytes.str = b
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return &m.inputBytes
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}
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func (m *machine) newInputString(s string) input {
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m.inputString.str = s
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return &m.inputString
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}
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func (m *machine) newInputReader(r io.RuneReader) input {
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m.inputReader.r = r
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m.inputReader.atEOT = false
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m.inputReader.pos = 0
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return &m.inputReader
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}
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// progMachine returns a new machine running the prog p.
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func progMachine(p *syntax.Prog) *machine {
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m := &machine{p: p}
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n := len(m.p.Inst)
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m.q0 = queue{make([]uint32, n), make([]entry, 0, n)}
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m.q1 = queue{make([]uint32, n), make([]entry, 0, n)}
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ncap := p.NumCap
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if ncap < 2 {
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ncap = 2
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}
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m.matchcap = make([]int, ncap)
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return m
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}
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func (m *machine) init(ncap int) {
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for _, t := range m.pool {
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t.cap = t.cap[:ncap]
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}
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m.matchcap = m.matchcap[:ncap]
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}
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// alloc allocates a new thread with the given instruction.
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// It uses the free pool if possible.
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func (m *machine) alloc(i *syntax.Inst) *thread {
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var t *thread
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if n := len(m.pool); n > 0 {
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t = m.pool[n-1]
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m.pool = m.pool[:n-1]
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} else {
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t = new(thread)
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t.cap = make([]int, len(m.matchcap), cap(m.matchcap))
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}
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t.inst = i
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return t
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}
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// free returns t to the free pool.
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func (m *machine) free(t *thread) {
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m.inputBytes.str = nil
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m.inputString.str = ""
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m.inputReader.r = nil
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m.pool = append(m.pool, t)
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}
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// match runs the machine over the input starting at pos.
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// It reports whether a match was found.
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// If so, m.matchcap holds the submatch information.
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func (m *machine) match(i input, pos int) bool {
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startCond := m.re.cond
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if startCond == ^syntax.EmptyOp(0) { // impossible
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return false
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}
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m.matched = false
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for i := range m.matchcap {
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m.matchcap[i] = -1
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}
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runq, nextq := &m.q0, &m.q1
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r, r1 := endOfText, endOfText
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width, width1 := 0, 0
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r, width = i.step(pos)
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if r != endOfText {
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r1, width1 = i.step(pos + width)
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}
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var flag syntax.EmptyOp
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if pos == 0 {
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flag = syntax.EmptyOpContext(-1, r)
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} else {
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flag = i.context(pos)
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}
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for {
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if len(runq.dense) == 0 {
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if startCond&syntax.EmptyBeginText != 0 && pos != 0 {
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// Anchored match, past beginning of text.
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break
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}
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if m.matched {
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// Have match; finished exploring alternatives.
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break
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}
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if len(m.re.prefix) > 0 && r1 != m.re.prefixRune && i.canCheckPrefix() {
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// Match requires literal prefix; fast search for it.
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advance := i.index(m.re, pos)
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if advance < 0 {
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break
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}
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pos += advance
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r, width = i.step(pos)
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r1, width1 = i.step(pos + width)
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}
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}
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if !m.matched {
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if len(m.matchcap) > 0 {
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m.matchcap[0] = pos
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}
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m.add(runq, uint32(m.p.Start), pos, m.matchcap, flag, nil)
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}
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flag = syntax.EmptyOpContext(r, r1)
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m.step(runq, nextq, pos, pos+width, r, flag)
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if width == 0 {
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break
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}
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if len(m.matchcap) == 0 && m.matched {
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// Found a match and not paying attention
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// to where it is, so any match will do.
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break
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}
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pos += width
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r, width = r1, width1
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if r != endOfText {
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r1, width1 = i.step(pos + width)
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}
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runq, nextq = nextq, runq
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}
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m.clear(nextq)
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return m.matched
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}
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// clear frees all threads on the thread queue.
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func (m *machine) clear(q *queue) {
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for _, d := range q.dense {
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if d.t != nil {
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// m.free(d.t)
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m.pool = append(m.pool, d.t)
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}
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}
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q.dense = q.dense[:0]
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}
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// step executes one step of the machine, running each of the threads
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// on runq and appending new threads to nextq.
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// The step processes the rune c (which may be endOfText),
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// which starts at position pos and ends at nextPos.
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// nextCond gives the setting for the empty-width flags after c.
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func (m *machine) step(runq, nextq *queue, pos, nextPos int, c rune, nextCond syntax.EmptyOp) {
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longest := m.re.longest
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for j := 0; j < len(runq.dense); j++ {
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d := &runq.dense[j]
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t := d.t
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if t == nil {
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continue
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}
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if longest && m.matched && len(t.cap) > 0 && m.matchcap[0] < t.cap[0] {
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// m.free(t)
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m.pool = append(m.pool, t)
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continue
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}
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i := t.inst
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add := false
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switch i.Op {
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default:
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panic("bad inst")
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case syntax.InstMatch:
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if len(t.cap) > 0 && (!longest || !m.matched || m.matchcap[1] < pos) {
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t.cap[1] = pos
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copy(m.matchcap, t.cap)
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}
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if !longest {
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// First-match mode: cut off all lower-priority threads.
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for _, d := range runq.dense[j+1:] {
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if d.t != nil {
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// m.free(d.t)
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m.pool = append(m.pool, d.t)
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}
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}
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runq.dense = runq.dense[:0]
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}
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m.matched = true
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case syntax.InstRune:
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add = i.MatchRune(c)
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case syntax.InstRune1:
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add = c == i.Rune[0]
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case syntax.InstRuneAny:
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add = true
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case syntax.InstRuneAnyNotNL:
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add = c != '\n'
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}
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if add {
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t = m.add(nextq, i.Out, nextPos, t.cap, nextCond, t)
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}
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if t != nil {
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// m.free(t)
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m.pool = append(m.pool, t)
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}
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}
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runq.dense = runq.dense[:0]
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}
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// add adds an entry to q for pc, unless the q already has such an entry.
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// It also recursively adds an entry for all instructions reachable from pc by following
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// empty-width conditions satisfied by cond. pos gives the current position
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// in the input.
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func (m *machine) add(q *queue, pc uint32, pos int, cap []int, cond syntax.EmptyOp, t *thread) *thread {
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if pc == 0 {
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return t
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}
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if j := q.sparse[pc]; j < uint32(len(q.dense)) && q.dense[j].pc == pc {
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return t
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}
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j := len(q.dense)
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q.dense = q.dense[:j+1]
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d := &q.dense[j]
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d.t = nil
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d.pc = pc
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q.sparse[pc] = uint32(j)
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i := &m.p.Inst[pc]
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switch i.Op {
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default:
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panic("unhandled")
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case syntax.InstFail:
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// nothing
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case syntax.InstAlt, syntax.InstAltMatch:
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t = m.add(q, i.Out, pos, cap, cond, t)
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t = m.add(q, i.Arg, pos, cap, cond, t)
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case syntax.InstEmptyWidth:
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if syntax.EmptyOp(i.Arg)&^cond == 0 {
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t = m.add(q, i.Out, pos, cap, cond, t)
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}
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case syntax.InstNop:
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t = m.add(q, i.Out, pos, cap, cond, t)
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case syntax.InstCapture:
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if int(i.Arg) < len(cap) {
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opos := cap[i.Arg]
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cap[i.Arg] = pos
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m.add(q, i.Out, pos, cap, cond, nil)
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cap[i.Arg] = opos
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} else {
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t = m.add(q, i.Out, pos, cap, cond, t)
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}
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case syntax.InstMatch, syntax.InstRune, syntax.InstRune1, syntax.InstRuneAny, syntax.InstRuneAnyNotNL:
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if t == nil {
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t = m.alloc(i)
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} else {
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t.inst = i
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}
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if len(cap) > 0 && &t.cap[0] != &cap[0] {
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copy(t.cap, cap)
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}
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d.t = t
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t = nil
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}
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return t
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}
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// empty is a non-nil 0-element slice,
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// so doExecute can avoid an allocation
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// when 0 captures are requested from a successful match.
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var empty = make([]int, 0)
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// doExecute finds the leftmost match in the input and returns
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// the position of its subexpressions.
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func (re *Regexp) doExecute(r io.RuneReader, b []byte, s string, pos int, ncap int) []int {
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m := re.get()
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var i input
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if r != nil {
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i = m.newInputReader(r)
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} else if b != nil {
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i = m.newInputBytes(b)
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} else {
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i = m.newInputString(s)
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}
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m.init(ncap)
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if !m.match(i, pos) {
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re.put(m)
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return nil
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}
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if ncap == 0 {
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re.put(m)
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return empty // empty but not nil
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}
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cap := make([]int, ncap)
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copy(cap, m.matchcap)
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re.put(m)
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return cap
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}
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