d8f412571f
From-SVN: r180552
307 lines
6.7 KiB
Go
307 lines
6.7 KiB
Go
package syntax
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import (
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"bytes"
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"strconv"
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"unicode"
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)
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// Compiled program.
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// May not belong in this package, but convenient for now.
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// A Prog is a compiled regular expression program.
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type Prog struct {
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Inst []Inst
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Start int // index of start instruction
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NumCap int // number of InstCapture insts in re
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}
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// An InstOp is an instruction opcode.
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type InstOp uint8
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const (
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InstAlt InstOp = iota
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InstAltMatch
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InstCapture
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InstEmptyWidth
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InstMatch
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InstFail
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InstNop
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InstRune
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InstRune1
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InstRuneAny
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InstRuneAnyNotNL
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)
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// An EmptyOp specifies a kind or mixture of zero-width assertions.
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type EmptyOp uint8
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const (
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EmptyBeginLine EmptyOp = 1 << iota
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EmptyEndLine
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EmptyBeginText
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EmptyEndText
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EmptyWordBoundary
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EmptyNoWordBoundary
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)
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// EmptyOpContext returns the zero-width assertions
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// satisfied at the position between the runes r1 and r2.
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// Passing r1 == -1 indicates that the position is
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// at the beginning of the text.
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// Passing r2 == -1 indicates that the position is
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// at the end of the text.
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func EmptyOpContext(r1, r2 int) EmptyOp {
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var op EmptyOp
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if r1 < 0 {
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op |= EmptyBeginText | EmptyBeginLine
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}
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if r1 == '\n' {
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op |= EmptyBeginLine
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}
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if r2 < 0 {
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op |= EmptyEndText | EmptyEndLine
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}
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if r2 == '\n' {
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op |= EmptyEndLine
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}
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if IsWordChar(r1) != IsWordChar(r2) {
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op |= EmptyWordBoundary
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} else {
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op |= EmptyNoWordBoundary
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}
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return op
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}
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// IsWordChar reports whether r is consider a ``word character''
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// during the evaluation of the \b and \B zero-width assertions.
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// These assertions are ASCII-only: the word characters are [A-Za-z0-9_].
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func IsWordChar(r int) bool {
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return 'A' <= r && r <= 'Z' || 'a' <= r && r <= 'z' || '0' <= r && r <= '9' || r == '_'
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}
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// An Inst is a single instruction in a regular expression program.
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type Inst struct {
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Op InstOp
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Out uint32 // all but InstMatch, InstFail
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Arg uint32 // InstAlt, InstAltMatch, InstCapture, InstEmptyWidth
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Rune []int
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}
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func (p *Prog) String() string {
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var b bytes.Buffer
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dumpProg(&b, p)
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return b.String()
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}
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// skipNop follows any no-op or capturing instructions
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// and returns the resulting pc.
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func (p *Prog) skipNop(pc uint32) *Inst {
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i := &p.Inst[pc]
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for i.Op == InstNop || i.Op == InstCapture {
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pc = i.Out
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i = &p.Inst[pc]
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}
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return i
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}
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// op returns i.Op but merges all the Rune special cases into InstRune
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func (i *Inst) op() InstOp {
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op := i.Op
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switch op {
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case InstRune1, InstRuneAny, InstRuneAnyNotNL:
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op = InstRune
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}
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return op
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}
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// Prefix returns a literal string that all matches for the
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// regexp must start with. Complete is true if the prefix
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// is the entire match.
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func (p *Prog) Prefix() (prefix string, complete bool) {
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i := p.skipNop(uint32(p.Start))
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// Avoid allocation of buffer if prefix is empty.
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if i.op() != InstRune || len(i.Rune) != 1 {
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return "", i.Op == InstMatch
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}
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// Have prefix; gather characters.
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var buf bytes.Buffer
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for i.op() == InstRune && len(i.Rune) == 1 && Flags(i.Arg)&FoldCase == 0 {
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buf.WriteRune(i.Rune[0])
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i = p.skipNop(i.Out)
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}
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return buf.String(), i.Op == InstMatch
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}
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// StartCond returns the leading empty-width conditions that must
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// be true in any match. It returns ^EmptyOp(0) if no matches are possible.
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func (p *Prog) StartCond() EmptyOp {
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var flag EmptyOp
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pc := uint32(p.Start)
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i := &p.Inst[pc]
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Loop:
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for {
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switch i.Op {
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case InstEmptyWidth:
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flag |= EmptyOp(i.Arg)
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case InstFail:
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return ^EmptyOp(0)
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case InstCapture, InstNop:
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// skip
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default:
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break Loop
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}
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pc = i.Out
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i = &p.Inst[pc]
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}
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return flag
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}
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// MatchRune returns true if the instruction matches (and consumes) r.
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// It should only be called when i.Op == InstRune.
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func (i *Inst) MatchRune(r int) bool {
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rune := i.Rune
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// Special case: single-rune slice is from literal string, not char class.
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if len(rune) == 1 {
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r0 := rune[0]
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if r == r0 {
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return true
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}
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if Flags(i.Arg)&FoldCase != 0 {
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for r1 := unicode.SimpleFold(r0); r1 != r0; r1 = unicode.SimpleFold(r1) {
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if r == r1 {
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return true
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}
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}
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}
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return false
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}
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// Peek at the first few pairs.
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// Should handle ASCII well.
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for j := 0; j < len(rune) && j <= 8; j += 2 {
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if r < rune[j] {
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return false
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}
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if r <= rune[j+1] {
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return true
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}
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}
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// Otherwise binary search.
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lo := 0
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hi := len(rune) / 2
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for lo < hi {
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m := lo + (hi-lo)/2
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if c := rune[2*m]; c <= r {
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if r <= rune[2*m+1] {
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return true
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}
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lo = m + 1
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} else {
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hi = m
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}
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}
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return false
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}
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// As per re2's Prog::IsWordChar. Determines whether rune is an ASCII word char.
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// Since we act on runes, it would be easy to support Unicode here.
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func wordRune(rune int) bool {
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return rune == '_' ||
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('A' <= rune && rune <= 'Z') ||
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('a' <= rune && rune <= 'z') ||
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('0' <= rune && rune <= '9')
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}
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// MatchEmptyWidth returns true if the instruction matches
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// an empty string between the runes before and after.
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// It should only be called when i.Op == InstEmptyWidth.
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func (i *Inst) MatchEmptyWidth(before int, after int) bool {
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switch EmptyOp(i.Arg) {
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case EmptyBeginLine:
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return before == '\n' || before == -1
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case EmptyEndLine:
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return after == '\n' || after == -1
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case EmptyBeginText:
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return before == -1
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case EmptyEndText:
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return after == -1
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case EmptyWordBoundary:
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return wordRune(before) != wordRune(after)
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case EmptyNoWordBoundary:
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return wordRune(before) == wordRune(after)
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}
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panic("unknown empty width arg")
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}
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func (i *Inst) String() string {
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var b bytes.Buffer
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dumpInst(&b, i)
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return b.String()
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}
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func bw(b *bytes.Buffer, args ...string) {
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for _, s := range args {
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b.WriteString(s)
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}
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}
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func dumpProg(b *bytes.Buffer, p *Prog) {
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for j := range p.Inst {
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i := &p.Inst[j]
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pc := strconv.Itoa(j)
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if len(pc) < 3 {
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b.WriteString(" "[len(pc):])
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}
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if j == p.Start {
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pc += "*"
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}
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bw(b, pc, "\t")
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dumpInst(b, i)
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bw(b, "\n")
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}
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}
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func u32(i uint32) string {
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return strconv.Uitoa64(uint64(i))
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}
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func dumpInst(b *bytes.Buffer, i *Inst) {
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switch i.Op {
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case InstAlt:
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bw(b, "alt -> ", u32(i.Out), ", ", u32(i.Arg))
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case InstAltMatch:
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bw(b, "altmatch -> ", u32(i.Out), ", ", u32(i.Arg))
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case InstCapture:
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bw(b, "cap ", u32(i.Arg), " -> ", u32(i.Out))
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case InstEmptyWidth:
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bw(b, "empty ", u32(i.Arg), " -> ", u32(i.Out))
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case InstMatch:
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bw(b, "match")
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case InstFail:
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bw(b, "fail")
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case InstNop:
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bw(b, "nop -> ", u32(i.Out))
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case InstRune:
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if i.Rune == nil {
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// shouldn't happen
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bw(b, "rune <nil>")
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}
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bw(b, "rune ", strconv.QuoteToASCII(string(i.Rune)))
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if Flags(i.Arg)&FoldCase != 0 {
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bw(b, "/i")
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}
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bw(b, " -> ", u32(i.Out))
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case InstRune1:
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bw(b, "rune1 ", strconv.QuoteToASCII(string(i.Rune)), " -> ", u32(i.Out))
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case InstRuneAny:
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bw(b, "any -> ", u32(i.Out))
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case InstRuneAnyNotNL:
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bw(b, "anynotnl -> ", u32(i.Out))
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}
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}
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