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