// OnePassPrefix returns a literal string that all matches for the
// regexp must start with. Complete is true if the prefix
// is the entire match. Pc is the index of the last rune instruction
// in the string. The OnePassPrefix skips over the mandatory
// EmptyBeginText
func onePassPrefix(p *syntax.Prog) (prefix string, complete bool, pc uint32) {
i := &p.Inst[p.Start]
if i.Op != syntax.InstEmptyWidth || (syntax.EmptyOp(i.Arg))&syntax.EmptyBeginText == 0 {
return "", i.Op == syntax.InstMatch, uint32(p.Start)
}
pc = i.Out
i = &p.Inst[pc]
for i.Op == syntax.InstNop {
pc = i.Out
i = &p.Inst[pc]
}
// Avoid allocation of buffer if prefix is empty.
if iop(i) != syntax.InstRune || len(i.Rune) != 1 {
return "", i.Op == syntax.InstMatch, uint32(p.Start)
}
// Have prefix; gather characters.
var buf bytes.Buffer
for iop(i) == syntax.InstRune && len(i.Rune) == 1 && syntax.Flags(i.Arg)&syntax.FoldCase == 0 {
buf.WriteRune(i.Rune[0])
pc, i = i.Out, &p.Inst[i.Out]
}
if i.Op == syntax.InstEmptyWidth &&
syntax.EmptyOp(i.Arg)&syntax.EmptyEndText != 0 &&
p.Inst[i.Out].Op == syntax.InstMatch {
complete = true
}
return buf.String(), complete, pc
}
// backtrack runs a backtracking search of prog on the input starting at pos.
func (m *machine) backtrack(i input, pos int, end int, ncap int) bool {
if !i.canCheckPrefix() {
panic("backtrack called for a RuneReader")
}
startCond := m.re.cond
if startCond == ^syntax.EmptyOp(0) { // impossible
return false
}
if startCond&syntax.EmptyBeginText != 0 && pos != 0 {
// Anchored match, past beginning of text.
return false
}
b := m.b
b.reset(end, ncap)
m.matchcap = m.matchcap[:ncap]
for i := range m.matchcap {
m.matchcap[i] = -1
}
// Anchored search must start at the beginning of the input
if startCond&syntax.EmptyBeginText != 0 {
if len(b.cap) > 0 {
b.cap[0] = pos
}
return m.tryBacktrack(b, i, uint32(m.p.Start), pos)
}
// Unanchored search, starting from each possible text position.
// Notice that we have to try the empty string at the end of
// the text, so the loop condition is pos <= end, not pos < end.
// This looks like it's quadratic in the size of the text,
// but we are not clearing visited between calls to TrySearch,
// so no work is duplicated and it ends up still being linear.
width := -1
for ; pos <= end && width != 0; pos += width {
if len(m.re.prefix) > 0 {
// Match requires literal prefix; fast search for it.
advance := i.index(m.re, pos)
if advance < 0 {
return false
}
pos += advance
}
if len(b.cap) > 0 {
b.cap[0] = pos
}
if m.tryBacktrack(b, i, uint32(m.p.Start), pos) {
// Match must be leftmost; done.
return true
}
_, width = i.step(pos)
}
return false
}
// compileOnePass returns a new *syntax.Prog suitable for onePass execution if the original Prog
// can be recharacterized as a one-pass regexp program, or syntax.notOnePass if the
// Prog cannot be converted. For a one pass prog, the fundamental condition that must
// be true is: at any InstAlt, there must be no ambiguity about what branch to take.
func compileOnePass(prog *syntax.Prog) (p *onePassProg) {
if prog.Start == 0 {
return notOnePass
}
// onepass regexp is anchored
if prog.Inst[prog.Start].Op != syntax.InstEmptyWidth ||
syntax.EmptyOp(prog.Inst[prog.Start].Arg)&syntax.EmptyBeginText != syntax.EmptyBeginText {
return notOnePass
}
// every instruction leading to InstMatch must be EmptyEndText
for _, inst := range prog.Inst {
opOut := prog.Inst[inst.Out].Op
switch inst.Op {
default:
if opOut == syntax.InstMatch {
return notOnePass
}
case syntax.InstAlt, syntax.InstAltMatch:
if opOut == syntax.InstMatch || prog.Inst[inst.Arg].Op == syntax.InstMatch {
return notOnePass
}
case syntax.InstEmptyWidth:
if opOut == syntax.InstMatch {
if syntax.EmptyOp(inst.Arg)&syntax.EmptyEndText == syntax.EmptyEndText {
continue
}
return notOnePass
}
}
}
// Creates a slightly optimized copy of the original Prog
// that cleans up some Prog idioms that block valid onepass programs
p = onePassCopy(prog)
// checkAmbiguity on InstAlts, build onepass Prog if possible
p = makeOnePass(p)
if p != notOnePass {
cleanupOnePass(p, prog)
}
return p
}
// 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
}
// onepass 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) onepass(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
}
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)
}
pc := m.op.Start
inst := m.op.Inst[pc]
// If there is a simple literal prefix, skip over it.
if pos == 0 && syntax.EmptyOp(inst.Arg)&^flag == 0 &&
len(m.re.prefix) > 0 && i.canCheckPrefix() {
// Match requires literal prefix; fast search for it.
if i.hasPrefix(m.re) {
pos += len(m.re.prefix)
r, width = i.step(pos)
r1, width1 = i.step(pos + width)
flag = i.context(pos)
pc = int(m.re.prefixEnd)
} else {
return m.matched
}
}
for {
inst = m.op.Inst[pc]
pc = int(inst.Out)
switch inst.Op {
default:
panic("bad inst")
case syntax.InstMatch:
m.matched = true
if len(m.matchcap) > 0 {
m.matchcap[0] = 0
m.matchcap[1] = pos
}
return m.matched
case syntax.InstRune:
if !inst.MatchRune(r) {
return m.matched
}
case syntax.InstRune1:
if r != inst.Rune[0] {
return m.matched
}
case syntax.InstRuneAny:
// Nothing
case syntax.InstRuneAnyNotNL:
if r == '\n' {
return m.matched
}
// 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:
return m.matched
case syntax.InstNop:
continue
case syntax.InstEmptyWidth:
if syntax.EmptyOp(inst.Arg)&^flag != 0 {
return m.matched
}
continue
case syntax.InstCapture:
if int(inst.Arg) < len(m.matchcap) {
m.matchcap[inst.Arg] = pos
}
continue
}
if width == 0 {
break
}
flag = syntax.EmptyOpContext(r, r1)
pos += width
r, width = r1, width1
if r != endOfText {
r1, width1 = i.step(pos + width)
}
}
return m.matched
}
// 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
}
// tryBacktrack runs a backtracking search starting at pos.
func (m *machine) tryBacktrack(b *bitState, i input, pc uint32, pos int) bool {
longest := m.re.longest
m.matched = false
b.push(pc, pos, 0)
for len(b.jobs) > 0 {
l := len(b.jobs) - 1
// Pop job off the stack.
pc := b.jobs[l].pc
pos := b.jobs[l].pos
arg := b.jobs[l].arg
b.jobs = b.jobs[:l]
// Optimization: rather than push and pop,
// code that is going to Push and continue
// the loop simply updates ip, p, and arg
// and jumps to CheckAndLoop. We have to
// do the ShouldVisit check that Push
// would have, but we avoid the stack
// manipulation.
goto Skip
CheckAndLoop:
if !b.shouldVisit(pc, pos) {
continue
}
Skip:
inst := b.prog.Inst[pc]
switch inst.Op {
default:
panic("bad inst")
case syntax.InstFail:
panic("unexpected InstFail")
case syntax.InstAlt:
// Cannot just
// b.push(inst.Out, pos, 0)
// b.push(inst.Arg, pos, 0)
// If during the processing of inst.Out, we encounter
// inst.Arg via another path, we want to process it then.
// Pushing it here will inhibit that. Instead, re-push
// inst with arg==1 as a reminder to push inst.Arg out
// later.
switch arg {
case 0:
b.push(pc, pos, 1)
pc = inst.Out
goto CheckAndLoop
case 1:
// Finished inst.Out; try inst.Arg.
arg = 0
pc = inst.Arg
goto CheckAndLoop
}
panic("bad arg in InstAlt")
case syntax.InstAltMatch:
// One opcode consumes runes; the other leads to match.
switch b.prog.Inst[inst.Out].Op {
case syntax.InstRune, syntax.InstRune1, syntax.InstRuneAny, syntax.InstRuneAnyNotNL:
// inst.Arg is the match.
b.push(inst.Arg, pos, 0)
pc = inst.Arg
pos = b.end
goto CheckAndLoop
}
// inst.Out is the match - non-greedy
b.push(inst.Out, b.end, 0)
pc = inst.Out
goto CheckAndLoop
case syntax.InstRune:
r, width := i.step(pos)
if !inst.MatchRune(r) {
continue
}
pos += width
pc = inst.Out
goto CheckAndLoop
case syntax.InstRune1:
r, width := i.step(pos)
if r != inst.Rune[0] {
continue
}
pos += width
pc = inst.Out
goto CheckAndLoop
case syntax.InstRuneAnyNotNL:
r, width := i.step(pos)
if r == '\n' || r == endOfText {
continue
}
pos += width
pc = inst.Out
goto CheckAndLoop
case syntax.InstRuneAny:
r, width := i.step(pos)
if r == endOfText {
continue
}
pos += width
pc = inst.Out
goto CheckAndLoop
case syntax.InstCapture:
switch arg {
case 0:
if 0 <= inst.Arg && inst.Arg < uint32(len(b.cap)) {
// Capture pos to register, but save old value.
b.push(pc, b.cap[inst.Arg], 1) // come back when we're done.
b.cap[inst.Arg] = pos
}
pc = inst.Out
goto CheckAndLoop
case 1:
// Finished inst.Out; restore the old value.
b.cap[inst.Arg] = pos
continue
}
panic("bad arg in InstCapture")
continue
case syntax.InstEmptyWidth:
if syntax.EmptyOp(inst.Arg)&^i.context(pos) != 0 {
continue
}
pc = inst.Out
goto CheckAndLoop
case syntax.InstNop:
pc = inst.Out
goto CheckAndLoop
case syntax.InstMatch:
// We found a match. If the caller doesn't care
// where the match is, no point going further.
if len(b.cap) == 0 {
m.matched = true
return m.matched
}
// Record best match so far.
// Only need to check end point, because this entire
// call is only considering one start position.
if len(b.cap) > 1 {
b.cap[1] = pos
}
if !m.matched || (longest && pos > 0 && pos > m.matchcap[1]) {
copy(m.matchcap, b.cap)
}
m.matched = true
// If going for first match, we're done.
if !longest {
return m.matched
}
// If we used the entire text, no longer match is possible.
if pos == b.end {
return m.matched
}
// Otherwise, continue on in hope of a longer match.
continue
}
panic("unreachable")
}
return m.matched
}
