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-rw-r--r--src/regexp/onepass.go507
1 files changed, 507 insertions, 0 deletions
diff --git a/src/regexp/onepass.go b/src/regexp/onepass.go
new file mode 100644
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--- /dev/null
+++ b/src/regexp/onepass.go
@@ -0,0 +1,507 @@
+// Copyright 2014 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 (
+ "regexp/syntax"
+ "sort"
+ "strings"
+ "unicode"
+ "unicode/utf8"
+)
+
+// "One-pass" regexp execution.
+// Some regexps can be analyzed to determine that they never need
+// backtracking: they are guaranteed to run in one pass over the string
+// without bothering to save all the usual NFA state.
+// Detect those and execute them more quickly.
+
+// A onePassProg is a compiled one-pass regular expression program.
+// It is the same as syntax.Prog except for the use of onePassInst.
+type onePassProg struct {
+ Inst []onePassInst
+ Start int // index of start instruction
+ NumCap int // number of InstCapture insts in re
+}
+
+// A onePassInst is a single instruction in a one-pass regular expression program.
+// It is the same as syntax.Inst except for the new 'Next' field.
+type onePassInst struct {
+ syntax.Inst
+ Next []uint32
+}
+
+// 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 strings.Builder
+ for iop(i) == syntax.InstRune && len(i.Rune) == 1 && syntax.Flags(i.Arg)&syntax.FoldCase == 0 && i.Rune[0] != utf8.RuneError {
+ 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
+}
+
+// OnePassNext selects the next actionable state of the prog, based on the input character.
+// It should only be called when i.Op == InstAlt or InstAltMatch, and from the one-pass machine.
+// One of the alternates may ultimately lead without input to end of line. If the instruction
+// is InstAltMatch the path to the InstMatch is in i.Out, the normal node in i.Next.
+func onePassNext(i *onePassInst, r rune) uint32 {
+ next := i.MatchRunePos(r)
+ if next >= 0 {
+ return i.Next[next]
+ }
+ if i.Op == syntax.InstAltMatch {
+ return i.Out
+ }
+ return 0
+}
+
+func iop(i *syntax.Inst) syntax.InstOp {
+ op := i.Op
+ switch op {
+ case syntax.InstRune1, syntax.InstRuneAny, syntax.InstRuneAnyNotNL:
+ op = syntax.InstRune
+ }
+ return op
+}
+
+// Sparse Array implementation is used as a queueOnePass.
+type queueOnePass struct {
+ sparse []uint32
+ dense []uint32
+ size, nextIndex uint32
+}
+
+func (q *queueOnePass) empty() bool {
+ return q.nextIndex >= q.size
+}
+
+func (q *queueOnePass) next() (n uint32) {
+ n = q.dense[q.nextIndex]
+ q.nextIndex++
+ return
+}
+
+func (q *queueOnePass) clear() {
+ q.size = 0
+ q.nextIndex = 0
+}
+
+func (q *queueOnePass) contains(u uint32) bool {
+ if u >= uint32(len(q.sparse)) {
+ return false
+ }
+ return q.sparse[u] < q.size && q.dense[q.sparse[u]] == u
+}
+
+func (q *queueOnePass) insert(u uint32) {
+ if !q.contains(u) {
+ q.insertNew(u)
+ }
+}
+
+func (q *queueOnePass) insertNew(u uint32) {
+ if u >= uint32(len(q.sparse)) {
+ return
+ }
+ q.sparse[u] = q.size
+ q.dense[q.size] = u
+ q.size++
+}
+
+func newQueue(size int) (q *queueOnePass) {
+ return &queueOnePass{
+ sparse: make([]uint32, size),
+ dense: make([]uint32, size),
+ }
+}
+
+// mergeRuneSets merges two non-intersecting runesets, and returns the merged result,
+// and a NextIp array. The idea is that if a rune matches the OnePassRunes at index
+// i, NextIp[i/2] is the target. If the input sets intersect, an empty runeset and a
+// NextIp array with the single element mergeFailed is returned.
+// The code assumes that both inputs contain ordered and non-intersecting rune pairs.
+const mergeFailed = uint32(0xffffffff)
+
+var (
+ noRune = []rune{}
+ noNext = []uint32{mergeFailed}
+)
+
+func mergeRuneSets(leftRunes, rightRunes *[]rune, leftPC, rightPC uint32) ([]rune, []uint32) {
+ leftLen := len(*leftRunes)
+ rightLen := len(*rightRunes)
+ if leftLen&0x1 != 0 || rightLen&0x1 != 0 {
+ panic("mergeRuneSets odd length []rune")
+ }
+ var (
+ lx, rx int
+ )
+ merged := make([]rune, 0)
+ next := make([]uint32, 0)
+ ok := true
+ defer func() {
+ if !ok {
+ merged = nil
+ next = nil
+ }
+ }()
+
+ ix := -1
+ extend := func(newLow *int, newArray *[]rune, pc uint32) bool {
+ if ix > 0 && (*newArray)[*newLow] <= merged[ix] {
+ return false
+ }
+ merged = append(merged, (*newArray)[*newLow], (*newArray)[*newLow+1])
+ *newLow += 2
+ ix += 2
+ next = append(next, pc)
+ return true
+ }
+
+ for lx < leftLen || rx < rightLen {
+ switch {
+ case rx >= rightLen:
+ ok = extend(&lx, leftRunes, leftPC)
+ case lx >= leftLen:
+ ok = extend(&rx, rightRunes, rightPC)
+ case (*rightRunes)[rx] < (*leftRunes)[lx]:
+ ok = extend(&rx, rightRunes, rightPC)
+ default:
+ ok = extend(&lx, leftRunes, leftPC)
+ }
+ if !ok {
+ return noRune, noNext
+ }
+ }
+ return merged, next
+}
+
+// cleanupOnePass drops working memory, and restores certain shortcut instructions.
+func cleanupOnePass(prog *onePassProg, original *syntax.Prog) {
+ for ix, instOriginal := range original.Inst {
+ switch instOriginal.Op {
+ case syntax.InstAlt, syntax.InstAltMatch, syntax.InstRune:
+ case syntax.InstCapture, syntax.InstEmptyWidth, syntax.InstNop, syntax.InstMatch, syntax.InstFail:
+ prog.Inst[ix].Next = nil
+ case syntax.InstRune1, syntax.InstRuneAny, syntax.InstRuneAnyNotNL:
+ prog.Inst[ix].Next = nil
+ prog.Inst[ix] = onePassInst{Inst: instOriginal}
+ }
+ }
+}
+
+// onePassCopy creates a copy of the original Prog, as we'll be modifying it
+func onePassCopy(prog *syntax.Prog) *onePassProg {
+ p := &onePassProg{
+ Start: prog.Start,
+ NumCap: prog.NumCap,
+ Inst: make([]onePassInst, len(prog.Inst)),
+ }
+ for i, inst := range prog.Inst {
+ p.Inst[i] = onePassInst{Inst: inst}
+ }
+
+ // rewrites one or more common Prog constructs that enable some otherwise
+ // non-onepass Progs to be onepass. A:BD (for example) means an InstAlt at
+ // ip A, that points to ips B & C.
+ // A:BC + B:DA => A:BC + B:CD
+ // A:BC + B:DC => A:DC + B:DC
+ for pc := range p.Inst {
+ switch p.Inst[pc].Op {
+ default:
+ continue
+ case syntax.InstAlt, syntax.InstAltMatch:
+ // A:Bx + B:Ay
+ p_A_Other := &p.Inst[pc].Out
+ p_A_Alt := &p.Inst[pc].Arg
+ // make sure a target is another Alt
+ instAlt := p.Inst[*p_A_Alt]
+ if !(instAlt.Op == syntax.InstAlt || instAlt.Op == syntax.InstAltMatch) {
+ p_A_Alt, p_A_Other = p_A_Other, p_A_Alt
+ instAlt = p.Inst[*p_A_Alt]
+ if !(instAlt.Op == syntax.InstAlt || instAlt.Op == syntax.InstAltMatch) {
+ continue
+ }
+ }
+ instOther := p.Inst[*p_A_Other]
+ // Analyzing both legs pointing to Alts is for another day
+ if instOther.Op == syntax.InstAlt || instOther.Op == syntax.InstAltMatch {
+ // too complicated
+ continue
+ }
+ // simple empty transition loop
+ // A:BC + B:DA => A:BC + B:DC
+ p_B_Alt := &p.Inst[*p_A_Alt].Out
+ p_B_Other := &p.Inst[*p_A_Alt].Arg
+ patch := false
+ if instAlt.Out == uint32(pc) {
+ patch = true
+ } else if instAlt.Arg == uint32(pc) {
+ patch = true
+ p_B_Alt, p_B_Other = p_B_Other, p_B_Alt
+ }
+ if patch {
+ *p_B_Alt = *p_A_Other
+ }
+
+ // empty transition to common target
+ // A:BC + B:DC => A:DC + B:DC
+ if *p_A_Other == *p_B_Alt {
+ *p_A_Alt = *p_B_Other
+ }
+ }
+ }
+ return p
+}
+
+// runeSlice exists to permit sorting the case-folded rune sets.
+type runeSlice []rune
+
+func (p runeSlice) Len() int { return len(p) }
+func (p runeSlice) Less(i, j int) bool { return p[i] < p[j] }
+func (p runeSlice) Swap(i, j int) { p[i], p[j] = p[j], p[i] }
+
+var anyRuneNotNL = []rune{0, '\n' - 1, '\n' + 1, unicode.MaxRune}
+var anyRune = []rune{0, unicode.MaxRune}
+
+// makeOnePass creates a onepass Prog, if possible. It is possible if at any alt,
+// the match engine can always tell which branch to take. The routine may modify
+// p if it is turned into a onepass Prog. If it isn't possible for this to be a
+// onepass Prog, the Prog nil is returned. makeOnePass is recursive
+// to the size of the Prog.
+func makeOnePass(p *onePassProg) *onePassProg {
+ // If the machine is very long, it's not worth the time to check if we can use one pass.
+ if len(p.Inst) >= 1000 {
+ return nil
+ }
+
+ var (
+ instQueue = newQueue(len(p.Inst))
+ visitQueue = newQueue(len(p.Inst))
+ check func(uint32, []bool) bool
+ onePassRunes = make([][]rune, len(p.Inst))
+ )
+
+ // check that paths from Alt instructions are unambiguous, and rebuild the new
+ // program as a onepass program
+ check = func(pc uint32, m []bool) (ok bool) {
+ ok = true
+ inst := &p.Inst[pc]
+ if visitQueue.contains(pc) {
+ return
+ }
+ visitQueue.insert(pc)
+ switch inst.Op {
+ case syntax.InstAlt, syntax.InstAltMatch:
+ ok = check(inst.Out, m) && check(inst.Arg, m)
+ // check no-input paths to InstMatch
+ matchOut := m[inst.Out]
+ matchArg := m[inst.Arg]
+ if matchOut && matchArg {
+ ok = false
+ break
+ }
+ // Match on empty goes in inst.Out
+ if matchArg {
+ inst.Out, inst.Arg = inst.Arg, inst.Out
+ matchOut, matchArg = matchArg, matchOut
+ }
+ if matchOut {
+ m[pc] = true
+ inst.Op = syntax.InstAltMatch
+ }
+
+ // build a dispatch operator from the two legs of the alt.
+ onePassRunes[pc], inst.Next = mergeRuneSets(
+ &onePassRunes[inst.Out], &onePassRunes[inst.Arg], inst.Out, inst.Arg)
+ if len(inst.Next) > 0 && inst.Next[0] == mergeFailed {
+ ok = false
+ break
+ }
+ case syntax.InstCapture, syntax.InstNop:
+ ok = check(inst.Out, m)
+ m[pc] = m[inst.Out]
+ // pass matching runes back through these no-ops.
+ onePassRunes[pc] = append([]rune{}, onePassRunes[inst.Out]...)
+ inst.Next = make([]uint32, len(onePassRunes[pc])/2+1)
+ for i := range inst.Next {
+ inst.Next[i] = inst.Out
+ }
+ case syntax.InstEmptyWidth:
+ ok = check(inst.Out, m)
+ m[pc] = m[inst.Out]
+ onePassRunes[pc] = append([]rune{}, onePassRunes[inst.Out]...)
+ inst.Next = make([]uint32, len(onePassRunes[pc])/2+1)
+ for i := range inst.Next {
+ inst.Next[i] = inst.Out
+ }
+ case syntax.InstMatch, syntax.InstFail:
+ m[pc] = inst.Op == syntax.InstMatch
+ case syntax.InstRune:
+ m[pc] = false
+ if len(inst.Next) > 0 {
+ break
+ }
+ instQueue.insert(inst.Out)
+ if len(inst.Rune) == 0 {
+ onePassRunes[pc] = []rune{}
+ inst.Next = []uint32{inst.Out}
+ break
+ }
+ runes := make([]rune, 0)
+ if len(inst.Rune) == 1 && syntax.Flags(inst.Arg)&syntax.FoldCase != 0 {
+ r0 := inst.Rune[0]
+ runes = append(runes, r0, r0)
+ for r1 := unicode.SimpleFold(r0); r1 != r0; r1 = unicode.SimpleFold(r1) {
+ runes = append(runes, r1, r1)
+ }
+ sort.Sort(runeSlice(runes))
+ } else {
+ runes = append(runes, inst.Rune...)
+ }
+ onePassRunes[pc] = runes
+ inst.Next = make([]uint32, len(onePassRunes[pc])/2+1)
+ for i := range inst.Next {
+ inst.Next[i] = inst.Out
+ }
+ inst.Op = syntax.InstRune
+ case syntax.InstRune1:
+ m[pc] = false
+ if len(inst.Next) > 0 {
+ break
+ }
+ instQueue.insert(inst.Out)
+ runes := []rune{}
+ // expand case-folded runes
+ if syntax.Flags(inst.Arg)&syntax.FoldCase != 0 {
+ r0 := inst.Rune[0]
+ runes = append(runes, r0, r0)
+ for r1 := unicode.SimpleFold(r0); r1 != r0; r1 = unicode.SimpleFold(r1) {
+ runes = append(runes, r1, r1)
+ }
+ sort.Sort(runeSlice(runes))
+ } else {
+ runes = append(runes, inst.Rune[0], inst.Rune[0])
+ }
+ onePassRunes[pc] = runes
+ inst.Next = make([]uint32, len(onePassRunes[pc])/2+1)
+ for i := range inst.Next {
+ inst.Next[i] = inst.Out
+ }
+ inst.Op = syntax.InstRune
+ case syntax.InstRuneAny:
+ m[pc] = false
+ if len(inst.Next) > 0 {
+ break
+ }
+ instQueue.insert(inst.Out)
+ onePassRunes[pc] = append([]rune{}, anyRune...)
+ inst.Next = []uint32{inst.Out}
+ case syntax.InstRuneAnyNotNL:
+ m[pc] = false
+ if len(inst.Next) > 0 {
+ break
+ }
+ instQueue.insert(inst.Out)
+ onePassRunes[pc] = append([]rune{}, anyRuneNotNL...)
+ inst.Next = make([]uint32, len(onePassRunes[pc])/2+1)
+ for i := range inst.Next {
+ inst.Next[i] = inst.Out
+ }
+ }
+ return
+ }
+
+ instQueue.clear()
+ instQueue.insert(uint32(p.Start))
+ m := make([]bool, len(p.Inst))
+ for !instQueue.empty() {
+ visitQueue.clear()
+ pc := instQueue.next()
+ if !check(pc, m) {
+ p = nil
+ break
+ }
+ }
+ if p != nil {
+ for i := range p.Inst {
+ p.Inst[i].Rune = onePassRunes[i]
+ }
+ }
+ return p
+}
+
+// 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.nil 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 nil
+ }
+ // onepass regexp is anchored
+ if prog.Inst[prog.Start].Op != syntax.InstEmptyWidth ||
+ syntax.EmptyOp(prog.Inst[prog.Start].Arg)&syntax.EmptyBeginText != syntax.EmptyBeginText {
+ return nil
+ }
+ // 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 nil
+ }
+ case syntax.InstAlt, syntax.InstAltMatch:
+ if opOut == syntax.InstMatch || prog.Inst[inst.Arg].Op == syntax.InstMatch {
+ return nil
+ }
+ case syntax.InstEmptyWidth:
+ if opOut == syntax.InstMatch {
+ if syntax.EmptyOp(inst.Arg)&syntax.EmptyEndText == syntax.EmptyEndText {
+ continue
+ }
+ return nil
+ }
+ }
+ }
+ // 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 != nil {
+ cleanupOnePass(p, prog)
+ }
+ return p
+}
generated by cgit v1.2.3 (git 2.39.1) at 2024-11-19 11:25:47 +0000