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// 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"
)
// 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
// cached inputs, to avoid allocation
inputBytes inputBytes
inputString inputString
inputReader inputReader
}
func (m *machine) newInputBytes(b []byte) input {
m.inputBytes.str = b
return &m.inputBytes
}
func (m *machine) newInputString(s string) input {
m.inputString.str = s
return &m.inputString
}
func (m *machine) newInputReader(r io.RuneReader) input {
m.inputReader.r = r
m.inputReader.atEOT = false
m.inputReader.pos = 0
return &m.inputReader
}
// 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
}
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
}
// free returns t to the free pool.
func (m *machine) free(t *thread) {
m.inputBytes.str = nil
m.inputString.str = ""
m.inputReader.r = nil
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
r, r1 := endOfText, endOfText
width, width1 := 0, 0
r, width = i.step(pos)
if r != endOfText {
r1, width1 = i.step(pos + width)
}
var flag syntax.EmptyOp
if pos == 0 {
flag = syntax.EmptyOpContext(-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 = syntax.EmptyOpContext(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.free(d.t)
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 syntax.EmptyOp) {
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.free(t)
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.free(d.t)
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.free(t)
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 syntax.EmptyOp, t *thread) *thread {
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)
t = m.add(q, i.Arg, pos, cap, cond, t)
case syntax.InstEmptyWidth:
if syntax.EmptyOp(i.Arg)&^cond == 0 {
t = m.add(q, i.Out, pos, cap, cond, t)
}
case syntax.InstNop:
t = m.add(q, i.Out, pos, cap, cond, t)
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 {
t = m.add(q, i.Out, pos, cap, cond, t)
}
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
}
// 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(r io.RuneReader, b []byte, s string, pos int, ncap int) []int {
m := re.get()
var i input
if r != nil {
i = m.newInputReader(r)
} else if b != nil {
i = m.newInputBytes(b)
} else {
i = m.newInputString(s)
}
m.init(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
}