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Source file src/regexp/exec.go

Documentation: regexp

     1  // Copyright 2011 The Go Authors. All rights reserved.
     2  // Use of this source code is governed by a BSD-style
     3  // license that can be found in the LICENSE file.
     4  
     5  package regexp
     6  
     7  import (
     8  	"io"
     9  	"regexp/syntax"
    10  	"sync"
    11  )
    12  
    13  // A queue is a 'sparse array' holding pending threads of execution.
    14  // See https://research.swtch.com/2008/03/using-uninitialized-memory-for-fun-and.html
    15  type queue struct {
    16  	sparse []uint32
    17  	dense  []entry
    18  }
    19  
    20  // An entry is an entry on a queue.
    21  // It holds both the instruction pc and the actual thread.
    22  // Some queue entries are just place holders so that the machine
    23  // knows it has considered that pc. Such entries have t == nil.
    24  type entry struct {
    25  	pc uint32
    26  	t  *thread
    27  }
    28  
    29  // A thread is the state of a single path through the machine:
    30  // an instruction and a corresponding capture array.
    31  // See https://swtch.com/~rsc/regexp/regexp2.html
    32  type thread struct {
    33  	inst *syntax.Inst
    34  	cap  []int
    35  }
    36  
    37  // A machine holds all the state during an NFA simulation for p.
    38  type machine struct {
    39  	re       *Regexp      // corresponding Regexp
    40  	p        *syntax.Prog // compiled program
    41  	q0, q1   queue        // two queues for runq, nextq
    42  	pool     []*thread    // pool of available threads
    43  	matched  bool         // whether a match was found
    44  	matchcap []int        // capture information for the match
    45  
    46  	inputs inputs
    47  }
    48  
    49  type inputs struct {
    50  	// cached inputs, to avoid allocation
    51  	bytes  inputBytes
    52  	string inputString
    53  	reader inputReader
    54  }
    55  
    56  func (i *inputs) newBytes(b []byte) input {
    57  	i.bytes.str = b
    58  	return &i.bytes
    59  }
    60  
    61  func (i *inputs) newString(s string) input {
    62  	i.string.str = s
    63  	return &i.string
    64  }
    65  
    66  func (i *inputs) newReader(r io.RuneReader) input {
    67  	i.reader.r = r
    68  	i.reader.atEOT = false
    69  	i.reader.pos = 0
    70  	return &i.reader
    71  }
    72  
    73  func (i *inputs) clear() {
    74  	// We need to clear 1 of these.
    75  	// Avoid the expense of clearing the others (pointer write barrier).
    76  	if i.bytes.str != nil {
    77  		i.bytes.str = nil
    78  	} else if i.reader.r != nil {
    79  		i.reader.r = nil
    80  	} else {
    81  		i.string.str = ""
    82  	}
    83  }
    84  
    85  func (i *inputs) init(r io.RuneReader, b []byte, s string) (input, int) {
    86  	if r != nil {
    87  		return i.newReader(r), 0
    88  	}
    89  	if b != nil {
    90  		return i.newBytes(b), len(b)
    91  	}
    92  	return i.newString(s), len(s)
    93  }
    94  
    95  func (m *machine) init(ncap int) {
    96  	for _, t := range m.pool {
    97  		t.cap = t.cap[:ncap]
    98  	}
    99  	m.matchcap = m.matchcap[:ncap]
   100  }
   101  
   102  // alloc allocates a new thread with the given instruction.
   103  // It uses the free pool if possible.
   104  func (m *machine) alloc(i *syntax.Inst) *thread {
   105  	var t *thread
   106  	if n := len(m.pool); n > 0 {
   107  		t = m.pool[n-1]
   108  		m.pool = m.pool[:n-1]
   109  	} else {
   110  		t = new(thread)
   111  		t.cap = make([]int, len(m.matchcap), cap(m.matchcap))
   112  	}
   113  	t.inst = i
   114  	return t
   115  }
   116  
   117  // A lazyFlag is a lazily-evaluated syntax.EmptyOp,
   118  // for checking zero-width flags like ^ $ \A \z \B \b.
   119  // It records the pair of relevant runes and does not
   120  // determine the implied flags until absolutely necessary
   121  // (most of the time, that means never).
   122  type lazyFlag uint64
   123  
   124  func newLazyFlag(r1, r2 rune) lazyFlag {
   125  	return lazyFlag(uint64(r1)<<32 | uint64(uint32(r2)))
   126  }
   127  
   128  func (f lazyFlag) match(op syntax.EmptyOp) bool {
   129  	if op == 0 {
   130  		return true
   131  	}
   132  	r1 := rune(f >> 32)
   133  	if op&syntax.EmptyBeginLine != 0 {
   134  		if r1 != '\n' && r1 >= 0 {
   135  			return false
   136  		}
   137  		op &^= syntax.EmptyBeginLine
   138  	}
   139  	if op&syntax.EmptyBeginText != 0 {
   140  		if r1 >= 0 {
   141  			return false
   142  		}
   143  		op &^= syntax.EmptyBeginText
   144  	}
   145  	if op == 0 {
   146  		return true
   147  	}
   148  	r2 := rune(f)
   149  	if op&syntax.EmptyEndLine != 0 {
   150  		if r2 != '\n' && r2 >= 0 {
   151  			return false
   152  		}
   153  		op &^= syntax.EmptyEndLine
   154  	}
   155  	if op&syntax.EmptyEndText != 0 {
   156  		if r2 >= 0 {
   157  			return false
   158  		}
   159  		op &^= syntax.EmptyEndText
   160  	}
   161  	if op == 0 {
   162  		return true
   163  	}
   164  	if syntax.IsWordChar(r1) != syntax.IsWordChar(r2) {
   165  		op &^= syntax.EmptyWordBoundary
   166  	} else {
   167  		op &^= syntax.EmptyNoWordBoundary
   168  	}
   169  	return op == 0
   170  }
   171  
   172  // match runs the machine over the input starting at pos.
   173  // It reports whether a match was found.
   174  // If so, m.matchcap holds the submatch information.
   175  func (m *machine) match(i input, pos int) bool {
   176  	startCond := m.re.cond
   177  	if startCond == ^syntax.EmptyOp(0) { // impossible
   178  		return false
   179  	}
   180  	m.matched = false
   181  	for i := range m.matchcap {
   182  		m.matchcap[i] = -1
   183  	}
   184  	runq, nextq := &m.q0, &m.q1
   185  	r, r1 := endOfText, endOfText
   186  	width, width1 := 0, 0
   187  	r, width = i.step(pos)
   188  	if r != endOfText {
   189  		r1, width1 = i.step(pos + width)
   190  	}
   191  	var flag lazyFlag
   192  	if pos == 0 {
   193  		flag = newLazyFlag(-1, r)
   194  	} else {
   195  		flag = i.context(pos)
   196  	}
   197  	for {
   198  		if len(runq.dense) == 0 {
   199  			if startCond&syntax.EmptyBeginText != 0 && pos != 0 {
   200  				// Anchored match, past beginning of text.
   201  				break
   202  			}
   203  			if m.matched {
   204  				// Have match; finished exploring alternatives.
   205  				break
   206  			}
   207  			if len(m.re.prefix) > 0 && r1 != m.re.prefixRune && i.canCheckPrefix() {
   208  				// Match requires literal prefix; fast search for it.
   209  				advance := i.index(m.re, pos)
   210  				if advance < 0 {
   211  					break
   212  				}
   213  				pos += advance
   214  				r, width = i.step(pos)
   215  				r1, width1 = i.step(pos + width)
   216  			}
   217  		}
   218  		if !m.matched {
   219  			if len(m.matchcap) > 0 {
   220  				m.matchcap[0] = pos
   221  			}
   222  			m.add(runq, uint32(m.p.Start), pos, m.matchcap, &flag, nil)
   223  		}
   224  		flag = newLazyFlag(r, r1)
   225  		m.step(runq, nextq, pos, pos+width, r, &flag)
   226  		if width == 0 {
   227  			break
   228  		}
   229  		if len(m.matchcap) == 0 && m.matched {
   230  			// Found a match and not paying attention
   231  			// to where it is, so any match will do.
   232  			break
   233  		}
   234  		pos += width
   235  		r, width = r1, width1
   236  		if r != endOfText {
   237  			r1, width1 = i.step(pos + width)
   238  		}
   239  		runq, nextq = nextq, runq
   240  	}
   241  	m.clear(nextq)
   242  	return m.matched
   243  }
   244  
   245  // clear frees all threads on the thread queue.
   246  func (m *machine) clear(q *queue) {
   247  	for _, d := range q.dense {
   248  		if d.t != nil {
   249  			m.pool = append(m.pool, d.t)
   250  		}
   251  	}
   252  	q.dense = q.dense[:0]
   253  }
   254  
   255  // step executes one step of the machine, running each of the threads
   256  // on runq and appending new threads to nextq.
   257  // The step processes the rune c (which may be endOfText),
   258  // which starts at position pos and ends at nextPos.
   259  // nextCond gives the setting for the empty-width flags after c.
   260  func (m *machine) step(runq, nextq *queue, pos, nextPos int, c rune, nextCond *lazyFlag) {
   261  	longest := m.re.longest
   262  	for j := 0; j < len(runq.dense); j++ {
   263  		d := &runq.dense[j]
   264  		t := d.t
   265  		if t == nil {
   266  			continue
   267  		}
   268  		if longest && m.matched && len(t.cap) > 0 && m.matchcap[0] < t.cap[0] {
   269  			m.pool = append(m.pool, t)
   270  			continue
   271  		}
   272  		i := t.inst
   273  		add := false
   274  		switch i.Op {
   275  		default:
   276  			panic("bad inst")
   277  
   278  		case syntax.InstMatch:
   279  			if len(t.cap) > 0 && (!longest || !m.matched || m.matchcap[1] < pos) {
   280  				t.cap[1] = pos
   281  				copy(m.matchcap, t.cap)
   282  			}
   283  			if !longest {
   284  				// First-match mode: cut off all lower-priority threads.
   285  				for _, d := range runq.dense[j+1:] {
   286  					if d.t != nil {
   287  						m.pool = append(m.pool, d.t)
   288  					}
   289  				}
   290  				runq.dense = runq.dense[:0]
   291  			}
   292  			m.matched = true
   293  
   294  		case syntax.InstRune:
   295  			add = i.MatchRune(c)
   296  		case syntax.InstRune1:
   297  			add = c == i.Rune[0]
   298  		case syntax.InstRuneAny:
   299  			add = true
   300  		case syntax.InstRuneAnyNotNL:
   301  			add = c != '\n'
   302  		}
   303  		if add {
   304  			t = m.add(nextq, i.Out, nextPos, t.cap, nextCond, t)
   305  		}
   306  		if t != nil {
   307  			m.pool = append(m.pool, t)
   308  		}
   309  	}
   310  	runq.dense = runq.dense[:0]
   311  }
   312  
   313  // add adds an entry to q for pc, unless the q already has such an entry.
   314  // It also recursively adds an entry for all instructions reachable from pc by following
   315  // empty-width conditions satisfied by cond.  pos gives the current position
   316  // in the input.
   317  func (m *machine) add(q *queue, pc uint32, pos int, cap []int, cond *lazyFlag, t *thread) *thread {
   318  Again:
   319  	if pc == 0 {
   320  		return t
   321  	}
   322  	if j := q.sparse[pc]; j < uint32(len(q.dense)) && q.dense[j].pc == pc {
   323  		return t
   324  	}
   325  
   326  	j := len(q.dense)
   327  	q.dense = q.dense[:j+1]
   328  	d := &q.dense[j]
   329  	d.t = nil
   330  	d.pc = pc
   331  	q.sparse[pc] = uint32(j)
   332  
   333  	i := &m.p.Inst[pc]
   334  	switch i.Op {
   335  	default:
   336  		panic("unhandled")
   337  	case syntax.InstFail:
   338  		// nothing
   339  	case syntax.InstAlt, syntax.InstAltMatch:
   340  		t = m.add(q, i.Out, pos, cap, cond, t)
   341  		pc = i.Arg
   342  		goto Again
   343  	case syntax.InstEmptyWidth:
   344  		if cond.match(syntax.EmptyOp(i.Arg)) {
   345  			pc = i.Out
   346  			goto Again
   347  		}
   348  	case syntax.InstNop:
   349  		pc = i.Out
   350  		goto Again
   351  	case syntax.InstCapture:
   352  		if int(i.Arg) < len(cap) {
   353  			opos := cap[i.Arg]
   354  			cap[i.Arg] = pos
   355  			m.add(q, i.Out, pos, cap, cond, nil)
   356  			cap[i.Arg] = opos
   357  		} else {
   358  			pc = i.Out
   359  			goto Again
   360  		}
   361  	case syntax.InstMatch, syntax.InstRune, syntax.InstRune1, syntax.InstRuneAny, syntax.InstRuneAnyNotNL:
   362  		if t == nil {
   363  			t = m.alloc(i)
   364  		} else {
   365  			t.inst = i
   366  		}
   367  		if len(cap) > 0 && &t.cap[0] != &cap[0] {
   368  			copy(t.cap, cap)
   369  		}
   370  		d.t = t
   371  		t = nil
   372  	}
   373  	return t
   374  }
   375  
   376  type onePassMachine struct {
   377  	inputs   inputs
   378  	matchcap []int
   379  }
   380  
   381  var onePassPool sync.Pool
   382  
   383  func newOnePassMachine() *onePassMachine {
   384  	m, ok := onePassPool.Get().(*onePassMachine)
   385  	if !ok {
   386  		m = new(onePassMachine)
   387  	}
   388  	return m
   389  }
   390  
   391  func freeOnePassMachine(m *onePassMachine) {
   392  	m.inputs.clear()
   393  	onePassPool.Put(m)
   394  }
   395  
   396  // doOnePass implements r.doExecute using the one-pass execution engine.
   397  func (re *Regexp) doOnePass(ir io.RuneReader, ib []byte, is string, pos, ncap int, dstCap []int) []int {
   398  	startCond := re.cond
   399  	if startCond == ^syntax.EmptyOp(0) { // impossible
   400  		return nil
   401  	}
   402  
   403  	m := newOnePassMachine()
   404  	if cap(m.matchcap) < ncap {
   405  		m.matchcap = make([]int, ncap)
   406  	} else {
   407  		m.matchcap = m.matchcap[:ncap]
   408  	}
   409  
   410  	matched := false
   411  	for i := range m.matchcap {
   412  		m.matchcap[i] = -1
   413  	}
   414  
   415  	i, _ := m.inputs.init(ir, ib, is)
   416  
   417  	r, r1 := endOfText, endOfText
   418  	width, width1 := 0, 0
   419  	r, width = i.step(pos)
   420  	if r != endOfText {
   421  		r1, width1 = i.step(pos + width)
   422  	}
   423  	var flag lazyFlag
   424  	if pos == 0 {
   425  		flag = newLazyFlag(-1, r)
   426  	} else {
   427  		flag = i.context(pos)
   428  	}
   429  	pc := re.onepass.Start
   430  	inst := re.onepass.Inst[pc]
   431  	// If there is a simple literal prefix, skip over it.
   432  	if pos == 0 && flag.match(syntax.EmptyOp(inst.Arg)) &&
   433  		len(re.prefix) > 0 && i.canCheckPrefix() {
   434  		// Match requires literal prefix; fast search for it.
   435  		if !i.hasPrefix(re) {
   436  			goto Return
   437  		}
   438  		pos += len(re.prefix)
   439  		r, width = i.step(pos)
   440  		r1, width1 = i.step(pos + width)
   441  		flag = i.context(pos)
   442  		pc = int(re.prefixEnd)
   443  	}
   444  	for {
   445  		inst = re.onepass.Inst[pc]
   446  		pc = int(inst.Out)
   447  		switch inst.Op {
   448  		default:
   449  			panic("bad inst")
   450  		case syntax.InstMatch:
   451  			matched = true
   452  			if len(m.matchcap) > 0 {
   453  				m.matchcap[0] = 0
   454  				m.matchcap[1] = pos
   455  			}
   456  			goto Return
   457  		case syntax.InstRune:
   458  			if !inst.MatchRune(r) {
   459  				goto Return
   460  			}
   461  		case syntax.InstRune1:
   462  			if r != inst.Rune[0] {
   463  				goto Return
   464  			}
   465  		case syntax.InstRuneAny:
   466  			// Nothing
   467  		case syntax.InstRuneAnyNotNL:
   468  			if r == '\n' {
   469  				goto Return
   470  			}
   471  		// peek at the input rune to see which branch of the Alt to take
   472  		case syntax.InstAlt, syntax.InstAltMatch:
   473  			pc = int(onePassNext(&inst, r))
   474  			continue
   475  		case syntax.InstFail:
   476  			goto Return
   477  		case syntax.InstNop:
   478  			continue
   479  		case syntax.InstEmptyWidth:
   480  			if !flag.match(syntax.EmptyOp(inst.Arg)) {
   481  				goto Return
   482  			}
   483  			continue
   484  		case syntax.InstCapture:
   485  			if int(inst.Arg) < len(m.matchcap) {
   486  				m.matchcap[inst.Arg] = pos
   487  			}
   488  			continue
   489  		}
   490  		if width == 0 {
   491  			break
   492  		}
   493  		flag = newLazyFlag(r, r1)
   494  		pos += width
   495  		r, width = r1, width1
   496  		if r != endOfText {
   497  			r1, width1 = i.step(pos + width)
   498  		}
   499  	}
   500  
   501  Return:
   502  	if !matched {
   503  		freeOnePassMachine(m)
   504  		return nil
   505  	}
   506  
   507  	dstCap = append(dstCap, m.matchcap...)
   508  	freeOnePassMachine(m)
   509  	return dstCap
   510  }
   511  
   512  // doMatch reports whether either r, b or s match the regexp.
   513  func (re *Regexp) doMatch(r io.RuneReader, b []byte, s string) bool {
   514  	return re.doExecute(r, b, s, 0, 0, nil) != nil
   515  }
   516  
   517  // doExecute finds the leftmost match in the input, appends the position
   518  // of its subexpressions to dstCap and returns dstCap.
   519  //
   520  // nil is returned if no matches are found and non-nil if matches are found.
   521  func (re *Regexp) doExecute(r io.RuneReader, b []byte, s string, pos int, ncap int, dstCap []int) []int {
   522  	if dstCap == nil {
   523  		// Make sure 'return dstCap' is non-nil.
   524  		dstCap = arrayNoInts[:0:0]
   525  	}
   526  
   527  	if re.onepass != nil {
   528  		return re.doOnePass(r, b, s, pos, ncap, dstCap)
   529  	}
   530  	if r == nil && len(b)+len(s) < re.maxBitStateLen {
   531  		return re.backtrack(b, s, pos, ncap, dstCap)
   532  	}
   533  
   534  	m := re.get()
   535  	i, _ := m.inputs.init(r, b, s)
   536  
   537  	m.init(ncap)
   538  	if !m.match(i, pos) {
   539  		re.put(m)
   540  		return nil
   541  	}
   542  
   543  	dstCap = append(dstCap, m.matchcap...)
   544  	re.put(m)
   545  	return dstCap
   546  }
   547  
   548  // arrayNoInts is returned by doExecute match if nil dstCap is passed
   549  // to it with ncap=0.
   550  var arrayNoInts [0]int
   551  

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