// Copyright 2011 The Go Authors. All rights reserved.
// Use of this source code is governed by a BSD-style
// license that can be found in the LICENSE file.
package regexp
import (
"io"
"regexp/syntax"
"sync"
)
// A queue is a 'sparse array' holding pending threads of execution.
// See https://research.swtch.com/2008/03/using-uninitialized-memory-for-fun-and.html
type queue struct {
sparse []uint32
dense []entry
}
// An 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 https://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
inputs inputs
}
type inputs struct {
// cached inputs, to avoid allocation
bytes inputBytes
string inputString
reader inputReader
}
func (i *inputs) newBytes(b []byte) input {
i.bytes.str = b
return &i.bytes
}
func (i *inputs) newString(s string) input {
i.string.str = s
return &i.string
}
func (i *inputs) newReader(r io.RuneReader) input {
i.reader.r = r
i.reader.atEOT = false
i.reader.pos = 0
return &i.reader
}
func (i *inputs) clear() {
// We need to clear 1 of these.
// Avoid the expense of clearing the others (pointer write barrier).
if i.bytes.str != nil {
i.bytes.str = nil
} else if i.reader.r != nil {
i.reader.r = nil
} else {
i.string.str = ""
}
}
func (i *inputs) init(r io.RuneReader, b []byte, s string) (input, int) {
if r != nil {
return i.newReader(r), 0
}
if b != nil {
return i.newBytes(b), len(b)
}
return i.newString(s), len(s)
}
func (m *machine) init(ncap int) {
for _, t := range m.pool {
t.cap = t.cap[:ncap]
}
m.matchcap = m.matchcap[:ncap]
}
// 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, len(m.matchcap), cap(m.matchcap))
}
t.inst = i
return t
}
// A lazyFlag is a lazily-evaluated syntax.EmptyOp,
// for checking zero-width flags like ^ $ \A \z \B \b.
// It records the pair of relevant runes and does not
// determine the implied flags until absolutely necessary
// (most of the time, that means never).
type lazyFlag uint64
func newLazyFlag(r1, r2 rune) lazyFlag {
return lazyFlag(uint64(r1)<<32 | uint64(uint32(r2)))
}
func (f lazyFlag) match(op syntax.EmptyOp) bool {
if op == 0 {
return true
}
r1 := rune(f >> 32)
if op&syntax.EmptyBeginLine != 0 {
if r1 != '\n' && r1 >= 0 {
return false
}
op &^= syntax.EmptyBeginLine
}
if op&syntax.EmptyBeginText != 0 {
if r1 >= 0 {
return false
}
op &^= syntax.EmptyBeginText
}
if op == 0 {
return true
}
r2 := rune(f)
if op&syntax.EmptyEndLine != 0 {
if r2 != '\n' && r2 >= 0 {
return false
}
op &^= syntax.EmptyEndLine
}
if op&syntax.EmptyEndText != 0 {
if r2 >= 0 {
return false
}
op &^= syntax.EmptyEndText
}
if op == 0 {
return true
}
if syntax.IsWordChar(r1) != syntax.IsWordChar(r2) {
op &^= syntax.EmptyWordBoundary
} else {
op &^= syntax.EmptyNoWordBoundary
}
return op == 0
}
// 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
r, r1 := endOfText, endOfText
width, width1 := 0, 0
r, width = i.step(pos)
if r != endOfText {
r1, width1 = i.step(pos + width)
}
var flag lazyFlag
if pos == 0 {
flag = newLazyFlag(-1, r)
} else {
flag = i.context(pos)
}
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 && r1 != 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
r, width = i.step(pos)
r1, 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, nil)
}
flag = newLazyFlag(r, r1)
m.step(runq, nextq, pos, pos+width, r, &flag)
if width == 0 {
break
}
if len(m.matchcap) == 0 && m.matched {
// Found a match and not paying attention
// to where it is, so any match will do.
break
}
pos += width
r, width = r1, width1
if r != endOfText {
r1, 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.pool = append(m.pool, 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 int, c rune, nextCond *lazyFlag) {
longest := m.re.longest
for j := 0; j < len(runq.dense); j++ {
d := &runq.dense[j]
t := d.t
if t == nil {
continue
}
if longest && m.matched && len(t.cap) > 0 && m.matchcap[0] < t.cap[0] {
m.pool = append(m.pool, t)
continue
}
i := t.inst
add := false
switch i.Op {
default:
panic("bad inst")
case syntax.InstMatch:
if len(t.cap) > 0 && (!longest || !m.matched || m.matchcap[1] < pos) {
t.cap[1] = pos
copy(m.matchcap, t.cap)
}
if !longest {
// First-match mode: cut off all lower-priority threads.
for _, d := range runq.dense[j+1:] {
if d.t != nil {
m.pool = append(m.pool, d.t)
}
}
runq.dense = runq.dense[:0]
}
m.matched = true
case syntax.InstRune:
add = i.MatchRune(c)
case syntax.InstRune1:
add = c == i.Rune[0]
case syntax.InstRuneAny:
add = true
case syntax.InstRuneAnyNotNL:
add = c != '\n'
}
if add {
t = m.add(nextq, i.Out, nextPos, t.cap, nextCond, t)
}
if t != nil {
m.pool = append(m.pool, 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 *lazyFlag, t *thread) *thread {
Again:
if pc == 0 {
return t
}
if j := q.sparse[pc]; j < uint32(len(q.dense)) && q.dense[j].pc == pc {
return t
}
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:
t = m.add(q, i.Out, pos, cap, cond, t)
pc = i.Arg
goto Again
case syntax.InstEmptyWidth:
if cond.match(syntax.EmptyOp(i.Arg)) {
pc = i.Out
goto Again
}
case syntax.InstNop:
pc = i.Out
goto Again
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, nil)
cap[i.Arg] = opos
} else {
pc = i.Out
goto Again
}
case syntax.InstMatch, syntax.InstRune, syntax.InstRune1, syntax.InstRuneAny, syntax.InstRuneAnyNotNL:
if t == nil {
t = m.alloc(i)
} else {
t.inst = i
}
if len(cap) > 0 && &t.cap[0] != &cap[0] {
copy(t.cap, cap)
}
d.t = t
t = nil
}
return t
}
type onePassMachine struct {
inputs inputs
matchcap []int
}
var onePassPool sync.Pool
func newOnePassMachine() *onePassMachine {
m, ok := onePassPool.Get().(*onePassMachine)
if !ok {
m = new(onePassMachine)
}
return m
}
func freeOnePassMachine(m *onePassMachine) {
m.inputs.clear()
onePassPool.Put(m)
}
// doOnePass implements r.doExecute using the one-pass execution engine.
func (re *Regexp) doOnePass(ir io.RuneReader, ib []byte, is string, pos, ncap int, dstCap []int) []int {
startCond := re.cond
if startCond == ^syntax.EmptyOp(0) { // impossible
return nil
}
m := newOnePassMachine()
if cap(m.matchcap) < ncap {
m.matchcap = make([]int, ncap)
} else {
m.matchcap = m.matchcap[:ncap]
}
matched := false
for i := range m.matchcap {
m.matchcap[i] = -1
}
i, _ := m.inputs.init(ir, ib, is)
r, r1 := endOfText, endOfText
width, width1 := 0, 0
r, width = i.step(pos)
if r != endOfText {
r1, width1 = i.step(pos + width)
}
var flag lazyFlag
if pos == 0 {
flag = newLazyFlag(-1, r)
} else {
flag = i.context(pos)
}
pc := re.onepass.Start
inst := re.onepass.Inst[pc]
// If there is a simple literal prefix, skip over it.
if pos == 0 && flag.match(syntax.EmptyOp(inst.Arg)) &&
len(re.prefix) > 0 && i.canCheckPrefix() {
// Match requires literal prefix; fast search for it.
if !i.hasPrefix(re) {
goto Return
}
pos += len(re.prefix)
r, width = i.step(pos)
r1, width1 = i.step(pos + width)
flag = i.context(pos)
pc = int(re.prefixEnd)
}
for {
inst = re.onepass.Inst[pc]
pc = int(inst.Out)
switch inst.Op {
default:
panic("bad inst")
case syntax.InstMatch:
matched = true
if len(m.matchcap) > 0 {
m.matchcap[0] = 0
m.matchcap[1] = pos
}
goto Return
case syntax.InstRune:
if !inst.MatchRune(r) {
goto Return
}
case syntax.InstRune1:
if r != inst.Rune[0] {
goto Return
}
case syntax.InstRuneAny:
// Nothing
case syntax.InstRuneAnyNotNL:
if r == '\n' {
goto Return
}
// peek at the input rune to see which branch of the Alt to take
case syntax.InstAlt, syntax.InstAltMatch:
pc = int(onePassNext(&inst, r))
continue
case syntax.InstFail:
goto Return
case syntax.InstNop:
continue
case syntax.InstEmptyWidth:
if !flag.match(syntax.EmptyOp(inst.Arg)) {
goto Return
}
continue
case syntax.InstCapture:
if int(inst.Arg) < len(m.matchcap) {
m.matchcap[inst.Arg] = pos
}
continue
}
if width == 0 {
break
}
flag = newLazyFlag(r, r1)
pos += width
r, width = r1, width1
if r != endOfText {
r1, width1 = i.step(pos + width)
}
}
Return:
if !matched {
freeOnePassMachine(m)
return nil
}
dstCap = append(dstCap, m.matchcap...)
freeOnePassMachine(m)
return dstCap
}
// doMatch reports whether either r, b or s match the regexp.
func (re *Regexp) doMatch(r io.RuneReader, b []byte, s string) bool {
return re.doExecute(r, b, s, 0, 0, nil) != nil
}
// doExecute finds the leftmost match in the input, appends the position
// of its subexpressions to dstCap and returns dstCap.
//
// nil is returned if no matches are found and non-nil if matches are found.
func (re *Regexp) doExecute(r io.RuneReader, b []byte, s string, pos int, ncap int, dstCap []int) []int {
if dstCap == nil {
// Make sure 'return dstCap' is non-nil.
dstCap = arrayNoInts[:0:0]
}
if r == nil && len(b)+len(s) < re.minInputLen {
return nil
}
if re.onepass != nil {
return re.doOnePass(r, b, s, pos, ncap, dstCap)
}
if r == nil && len(b)+len(s) < re.maxBitStateLen {
return re.backtrack(b, s, pos, ncap, dstCap)
}
m := re.get()
i, _ := m.inputs.init(r, b, s)
m.init(ncap)
if !m.match(i, pos) {
re.put(m)
return nil
}
dstCap = append(dstCap, m.matchcap...)
re.put(m)
return dstCap
}
// arrayNoInts is returned by doExecute match if nil dstCap is passed
// to it with ncap=0.
var arrayNoInts [0]int
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