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-rw-r--r--src/pkg/regexp/exec.go345
1 files changed, 345 insertions, 0 deletions
diff --git a/src/pkg/regexp/exec.go b/src/pkg/regexp/exec.go
new file mode 100644
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--- /dev/null
+++ b/src/pkg/regexp/exec.go
@@ -0,0 +1,345 @@
+// 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
+}
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