Imported Upstream version 60upstream/60

1 files changed, 1488 insertions, 0 deletions

diff --git a/src/pkg/regexp/regexp.go b/src/pkg/regexp/regexp.go
new file mode 100644
index 000000000..e8d4c087c
--- /dev/null
+++ b/src/pkg/regexp/regexp.go
@@ -0,0 +1,1488 @@
+// Use of this source code is governed by a BSD-style
+// license that can be found in the LICENSE file.
+
+// Package regexp implements a simple regular expression library.
+//
+// The syntax of the regular expressions accepted is:
+//
+//	regexp:
+//		concatenation { '|' concatenation }
+//	concatenation:
+//		{ closure }
+//	closure:
+//		term [ '*' | '+' | '?' ]
+//	term:
+//		'^'
+//		'$'
+//		'.'
+//		character
+//		'[' [ '^' ] { character-range } ']'
+//		'(' regexp ')'
+//	character-range:
+//		character [ '-' character ]
+//
+// All characters are UTF-8-encoded code points.  Backslashes escape special
+// characters, including inside character classes.  The standard Go character
+// escapes are also recognized: \a \b \f \n \r \t \v.
+//
+// There are 16 methods of Regexp that match a regular expression and identify
+// the matched text.  Their names are matched by this regular expression:
+//
+//	Find(All)?(String)?(Submatch)?(Index)?
+//
+// If 'All' is present, the routine matches successive non-overlapping
+// matches of the entire expression.  Empty matches abutting a preceding
+// match are ignored.  The return value is a slice containing the successive
+// return values of the corresponding non-'All' routine.  These routines take
+// an extra integer argument, n; if n >= 0, the function returns at most n
+// matches/submatches.
+//
+// If 'String' is present, the argument is a string; otherwise it is a slice
+// of bytes; return values are adjusted as appropriate.
+//
+// If 'Submatch' is present, the return value is a slice identifying the
+// successive submatches of the expression.  Submatches are matches of
+// parenthesized subexpressions within the regular expression, numbered from
+// left to right in order of opening parenthesis.  Submatch 0 is the match of
+// the entire expression, submatch 1 the match of the first parenthesized
+// subexpression, and so on.
+//
+// If 'Index' is present, matches and submatches are identified by byte index
+// pairs within the input string: result[2*n:2*n+1] identifies the indexes of
+// the nth submatch.  The pair for n==0 identifies the match of the entire
+// expression.  If 'Index' is not present, the match is identified by the
+// text of the match/submatch.  If an index is negative, it means that
+// subexpression did not match any string in the input.
+//
+// There is also a subset of the methods that can be applied to text read
+// from a RuneReader:
+//
+//	MatchReader, FindReaderIndex, FindReaderSubmatchIndex
+//
+// This set may grow.  Note that regular expression matches may need to
+// examine text beyond the text returned by a match, so the methods that
+// match text from a RuneReader may read arbitrarily far into the input
+// before returning.
+//
+// (There are a few other methods that do not match this pattern.)
+//
+package regexp
+
+import (
+	"bytes"
+	"io"
+	"os"
+	"strings"
+	"utf8"
+)
+
+var debug = false
+
+// Error is the local type for a parsing error.
+type Error string
+
+func (e Error) String() string {
+	return string(e)
+}
+
+// Error codes returned by failures to parse an expression.
+var (
+	ErrInternal            = Error("regexp: internal error")
+	ErrUnmatchedLpar       = Error("regexp: unmatched '('")
+	ErrUnmatchedRpar       = Error("regexp: unmatched ')'")
+	ErrUnmatchedLbkt       = Error("regexp: unmatched '['")
+	ErrUnmatchedRbkt       = Error("regexp: unmatched ']'")
+	ErrBadRange            = Error("regexp: bad range in character class")
+	ErrExtraneousBackslash = Error("regexp: extraneous backslash")
+	ErrBadClosure          = Error("regexp: repeated closure (**, ++, etc.)")
+	ErrBareClosure         = Error("regexp: closure applies to nothing")
+	ErrBadBackslash        = Error("regexp: illegal backslash escape")
+)
+
+const (
+	iStart     = iota // beginning of program
+	iEnd              // end of program: success
+	iBOT              // '^' beginning of text
+	iEOT              // '$' end of text
+	iChar             // 'a' regular character
+	iCharClass        // [a-z] character class
+	iAny              // '.' any character including newline
+	iNotNL            // [^\n] special case: any character but newline
+	iBra              // '(' parenthesized expression: 2*braNum for left, 2*braNum+1 for right
+	iAlt              // '|' alternation
+	iNop              // do nothing; makes it easy to link without patching
+)
+
+// An instruction executed by the NFA
+type instr struct {
+	kind  int    // the type of this instruction: iChar, iAny, etc.
+	index int    // used only in debugging; could be eliminated
+	next  *instr // the instruction to execute after this one
+	// Special fields valid only for some items.
+	char   int        // iChar
+	braNum int        // iBra, iEbra
+	cclass *charClass // iCharClass
+	left   *instr     // iAlt, other branch
+}
+
+func (i *instr) print() {
+	switch i.kind {
+	case iStart:
+		print("start")
+	case iEnd:
+		print("end")
+	case iBOT:
+		print("bot")
+	case iEOT:
+		print("eot")
+	case iChar:
+		print("char ", string(i.char))
+	case iCharClass:
+		i.cclass.print()
+	case iAny:
+		print("any")
+	case iNotNL:
+		print("notnl")
+	case iBra:
+		if i.braNum&1 == 0 {
+			print("bra", i.braNum/2)
+		} else {
+			print("ebra", i.braNum/2)
+		}
+	case iAlt:
+		print("alt(", i.left.index, ")")
+	case iNop:
+		print("nop")
+	}
+}
+
+// Regexp is the representation of a compiled regular expression.
+// The public interface is entirely through methods.
+// A Regexp is safe for concurrent use by multiple goroutines.
+type Regexp struct {
+	expr        string // the original expression
+	prefix      string // initial plain text string
+	prefixBytes []byte // initial plain text bytes
+	inst        []*instr
+	start       *instr // first instruction of machine
+	prefixStart *instr // where to start if there is a prefix
+	nbra        int    // number of brackets in expression, for subexpressions
+}
+
+type charClass struct {
+	negate bool // is character class negated? ([^a-z])
+	// slice of int, stored pairwise: [a-z] is (a,z); x is (x,x):
+	ranges     []int
+	cmin, cmax int
+}
+
+func (cclass *charClass) print() {
+	print("charclass")
+	if cclass.negate {
+		print(" (negated)")
+	}
+	for i := 0; i < len(cclass.ranges); i += 2 {
+		l := cclass.ranges[i]
+		r := cclass.ranges[i+1]
+		if l == r {
+			print(" [", string(l), "]")
+		} else {
+			print(" [", string(l), "-", string(r), "]")
+		}
+	}
+}
+
+func (cclass *charClass) addRange(a, b int) {
+	// range is a through b inclusive
+	cclass.ranges = append(cclass.ranges, a, b)
+	if a < cclass.cmin {
+		cclass.cmin = a
+	}
+	if b > cclass.cmax {
+		cclass.cmax = b
+	}
+}
+
+func (cclass *charClass) matches(c int) bool {
+	if c < cclass.cmin || c > cclass.cmax {
+		return cclass.negate
+	}
+	ranges := cclass.ranges
+	for i := 0; i < len(ranges); i = i + 2 {
+		if ranges[i] <= c && c <= ranges[i+1] {
+			return !cclass.negate
+		}
+	}
+	return cclass.negate
+}
+
+func newCharClass() *instr {
+	i := &instr{kind: iCharClass}
+	i.cclass = new(charClass)
+	i.cclass.ranges = make([]int, 0, 4)
+	i.cclass.cmin = 0x10FFFF + 1 // MaxRune + 1
+	i.cclass.cmax = -1
+	return i
+}
+
+func (re *Regexp) add(i *instr) *instr {
+	i.index = len(re.inst)
+	re.inst = append(re.inst, i)
+	return i
+}
+
+type parser struct {
+	re    *Regexp
+	nlpar int // number of unclosed lpars
+	pos   int
+	ch    int
+}
+
+func (p *parser) error(err Error) {
+	panic(err)
+}
+
+const endOfText = -1
+
+func (p *parser) c() int { return p.ch }
+
+func (p *parser) nextc() int {
+	if p.pos >= len(p.re.expr) {
+		p.ch = endOfText
+	} else {
+		c, w := utf8.DecodeRuneInString(p.re.expr[p.pos:])
+		p.ch = c
+		p.pos += w
+	}
+	return p.ch
+}
+
+func newParser(re *Regexp) *parser {
+	p := new(parser)
+	p.re = re
+	p.nextc() // load p.ch
+	return p
+}
+
+func special(c int) bool {
+	for _, r := range `\.+*?()|[]^$` {
+		if c == r {
+			return true
+		}
+	}
+	return false
+}
+
+func ispunct(c int) bool {
+	for _, r := range "!\"#$%&'()*+,-./:;<=>?@[\\]^_`{|}~" {
+		if c == r {
+			return true
+		}
+	}
+	return false
+}
+
+var escapes = []byte("abfnrtv")
+var escaped = []byte("\a\b\f\n\r\t\v")
+
+func escape(c int) int {
+	for i, b := range escapes {
+		if int(b) == c {
+			return i
+		}
+	}
+	return -1
+}
+
+func (p *parser) checkBackslash() int {
+	c := p.c()
+	if c == '\\' {
+		c = p.nextc()
+		switch {
+		case c == endOfText:
+			p.error(ErrExtraneousBackslash)
+		case ispunct(c):
+			// c is as delivered
+		case escape(c) >= 0:
+			c = int(escaped[escape(c)])
+		default:
+			p.error(ErrBadBackslash)
+		}
+	}
+	return c
+}
+
+func (p *parser) charClass() *instr {
+	i := newCharClass()
+	cc := i.cclass
+	if p.c() == '^' {
+		cc.negate = true
+		p.nextc()
+	}
+	left := -1
+	for {
+		switch c := p.c(); c {
+		case ']', endOfText:
+			if left >= 0 {
+				p.error(ErrBadRange)
+			}
+			// Is it [^\n]?
+			if cc.negate && len(cc.ranges) == 2 &&
+				cc.ranges[0] == '\n' && cc.ranges[1] == '\n' {
+				nl := &instr{kind: iNotNL}
+				p.re.add(nl)
+				return nl
+			}
+			// Special common case: "[a]" -> "a"
+			if !cc.negate && len(cc.ranges) == 2 && cc.ranges[0] == cc.ranges[1] {
+				c := &instr{kind: iChar, char: cc.ranges[0]}
+				p.re.add(c)
+				return c
+			}
+			p.re.add(i)
+			return i
+		case '-': // do this before backslash processing
+			p.error(ErrBadRange)
+		default:
+			c = p.checkBackslash()
+			p.nextc()
+			switch {
+			case left < 0: // first of pair
+				if p.c() == '-' { // range
+					p.nextc()
+					left = c
+				} else { // single char
+					cc.addRange(c, c)
+				}
+			case left <= c: // second of pair
+				cc.addRange(left, c)
+				left = -1
+			default:
+				p.error(ErrBadRange)
+			}
+		}
+	}
+	panic("unreachable")
+}
+
+func (p *parser) term() (start, end *instr) {
+	switch c := p.c(); c {
+	case '|', endOfText:
+		return nil, nil
+	case '*', '+', '?':
+		p.error(ErrBareClosure)
+	case ')':
+		if p.nlpar == 0 {
+			p.error(ErrUnmatchedRpar)
+		}
+		return nil, nil
+	case ']':
+		p.error(ErrUnmatchedRbkt)
+	case '^':
+		p.nextc()
+		start = p.re.add(&instr{kind: iBOT})
+		return start, start
+	case '$':
+		p.nextc()
+		start = p.re.add(&instr{kind: iEOT})
+		return start, start
+	case '.':
+		p.nextc()
+		start = p.re.add(&instr{kind: iAny})
+		return start, start
+	case '[':
+		p.nextc()
+		start = p.charClass()
+		if p.c() != ']' {
+			p.error(ErrUnmatchedLbkt)
+		}
+		p.nextc()
+		return start, start
+	case '(':
+		p.nextc()
+		p.nlpar++
+		p.re.nbra++ // increment first so first subexpr is \1
+		nbra := p.re.nbra
+		start, end = p.regexp()
+		if p.c() != ')' {
+			p.error(ErrUnmatchedLpar)
+		}
+		p.nlpar--
+		p.nextc()
+		bra := &instr{kind: iBra, braNum: 2 * nbra}
+		p.re.add(bra)
+		ebra := &instr{kind: iBra, braNum: 2*nbra + 1}
+		p.re.add(ebra)
+		if start == nil {
+			if end == nil {
+				p.error(ErrInternal)
+				return
+			}
+			start = ebra
+		} else {
+			end.next = ebra
+		}
+		bra.next = start
+		return bra, ebra
+	default:
+		c = p.checkBackslash()
+		p.nextc()
+		start = &instr{kind: iChar, char: c}
+		p.re.add(start)
+		return start, start
+	}
+	panic("unreachable")
+}
+
+func (p *parser) closure() (start, end *instr) {
+	start, end = p.term()
+	if start == nil {
+		return
+	}
+	switch p.c() {
+	case '*':
+		// (start,end)*:
+		alt := &instr{kind: iAlt}
+		p.re.add(alt)
+		end.next = alt   // after end, do alt
+		alt.left = start // alternate brach: return to start
+		start = alt      // alt becomes new (start, end)
+		end = alt
+	case '+':
+		// (start,end)+:
+		alt := &instr{kind: iAlt}
+		p.re.add(alt)
+		end.next = alt   // after end, do alt
+		alt.left = start // alternate brach: return to start
+		end = alt        // start is unchanged; end is alt
+	case '?':
+		// (start,end)?:
+		alt := &instr{kind: iAlt}
+		p.re.add(alt)
+		nop := &instr{kind: iNop}
+		p.re.add(nop)
+		alt.left = start // alternate branch is start
+		alt.next = nop   // follow on to nop
+		end.next = nop   // after end, go to nop
+		start = alt      // start is now alt
+		end = nop        // end is nop pointed to by both branches
+	default:
+		return
+	}
+	switch p.nextc() {
+	case '*', '+', '?':
+		p.error(ErrBadClosure)
+	}
+	return
+}
+
+func (p *parser) concatenation() (start, end *instr) {
+	for {
+		nstart, nend := p.closure()
+		switch {
+		case nstart == nil: // end of this concatenation
+			if start == nil { // this is the empty string
+				nop := p.re.add(&instr{kind: iNop})
+				return nop, nop
+			}
+			return
+		case start == nil: // this is first element of concatenation
+			start, end = nstart, nend
+		default:
+			end.next = nstart
+			end = nend
+		}
+	}
+	panic("unreachable")
+}
+
+func (p *parser) regexp() (start, end *instr) {
+	start, end = p.concatenation()
+	for {
+		switch p.c() {
+		default:
+			return
+		case '|':
+			p.nextc()
+			nstart, nend := p.concatenation()
+			alt := &instr{kind: iAlt}
+			p.re.add(alt)
+			alt.left = start
+			alt.next = nstart
+			nop := &instr{kind: iNop}
+			p.re.add(nop)
+			end.next = nop
+			nend.next = nop
+			start, end = alt, nop
+		}
+	}
+	panic("unreachable")
+}
+
+func unNop(i *instr) *instr {
+	for i.kind == iNop {
+		i = i.next
+	}
+	return i
+}
+
+func (re *Regexp) eliminateNops() {
+	for _, inst := range re.inst {
+		if inst.kind == iEnd {
+			continue
+		}
+		inst.next = unNop(inst.next)
+		if inst.kind == iAlt {
+			inst.left = unNop(inst.left)
+		}
+	}
+}
+
+func (re *Regexp) dump() {
+	print("prefix <", re.prefix, ">\n")
+	for _, inst := range re.inst {
+		print(inst.index, ": ")
+		inst.print()
+		if inst.kind != iEnd {
+			print(" -> ", inst.next.index)
+		}
+		print("\n")
+	}
+}
+
+func (re *Regexp) doParse() {
+	p := newParser(re)
+	start := &instr{kind: iStart}
+	re.add(start)
+	s, e := p.regexp()
+	start.next = s
+	re.start = start
+	e.next = re.add(&instr{kind: iEnd})
+
+	if debug {
+		re.dump()
+		println()
+	}
+
+	re.eliminateNops()
+	if debug {
+		re.dump()
+		println()
+	}
+	re.setPrefix()
+	if debug {
+		re.dump()
+		println()
+	}
+}
+
+// Extract regular text from the beginning of the pattern,
+// possibly after a leading iBOT.
+// That text can be used by doExecute to speed up matching.
+func (re *Regexp) setPrefix() {
+	var b []byte
+	var utf = make([]byte, utf8.UTFMax)
+	var inst *instr
+	// First instruction is start; skip that.  Also skip any initial iBOT.
+	inst = re.inst[0].next
+	for inst.kind == iBOT {
+		inst = inst.next
+	}
+Loop:
+	for ; inst.kind != iEnd; inst = inst.next {
+		// stop if this is not a char
+		if inst.kind != iChar {
+			break
+		}
+		// stop if this char can be followed by a match for an empty string,
+		// which includes closures, ^, and $.
+		switch inst.next.kind {
+		case iBOT, iEOT, iAlt:
+			break Loop
+		}
+		n := utf8.EncodeRune(utf, inst.char)
+		b = append(b, utf[0:n]...)
+	}
+	// point prefixStart instruction to first non-CHAR after prefix
+	re.prefixStart = inst
+	re.prefixBytes = b
+	re.prefix = string(b)
+}
+
+// String returns the source text used to compile the regular expression.
+func (re *Regexp) String() string {
+	return re.expr
+}
+
+// Compile parses a regular expression and returns, if successful, a Regexp
+// object that can be used to match against text.
+func Compile(str string) (regexp *Regexp, error os.Error) {
+	regexp = new(Regexp)
+	// doParse will panic if there is a parse error.
+	defer func() {
+		if e := recover(); e != nil {
+			regexp = nil
+			error = e.(Error) // Will re-panic if error was not an Error, e.g. nil-pointer exception
+		}
+	}()
+	regexp.expr = str
+	regexp.inst = make([]*instr, 0, 10)
+	regexp.doParse()
+	return
+}
+
+// MustCompile is like Compile but panics if the expression cannot be parsed.
+// It simplifies safe initialization of global variables holding compiled regular
+// expressions.
+func MustCompile(str string) *Regexp {
+	regexp, error := Compile(str)
+	if error != nil {
+		panic(`regexp: compiling "` + str + `": ` + error.String())
+	}
+	return regexp
+}
+
+// NumSubexp returns the number of parenthesized subexpressions in this Regexp.
+func (re *Regexp) NumSubexp() int { return re.nbra }
+
+// The match arena allows us to reduce the garbage generated by tossing
+// match vectors away as we execute.  Matches are ref counted and returned
+// to a free list when no longer active.  Increases a simple benchmark by 22X.
+type matchArena struct {
+	head  *matchVec
+	len   int // length of match vector
+	pos   int
+	atBOT bool // whether we're at beginning of text
+	atEOT bool // whether we're at end of text
+}
+
+type matchVec struct {
+	m    []int // pairs of bracketing submatches. 0th is start,end
+	ref  int
+	next *matchVec
+}
+
+func (a *matchArena) new() *matchVec {
+	if a.head == nil {
+		const N = 10
+		block := make([]matchVec, N)
+		for i := 0; i < N; i++ {
+			b := &block[i]
+			b.next = a.head
+			a.head = b
+		}
+	}
+	m := a.head
+	a.head = m.next
+	m.ref = 0
+	if m.m == nil {
+		m.m = make([]int, a.len)
+	}
+	return m
+}
+
+func (a *matchArena) free(m *matchVec) {
+	m.ref--
+	if m.ref == 0 {
+		m.next = a.head
+		a.head = m
+	}
+}
+
+func (a *matchArena) copy(m *matchVec) *matchVec {
+	m1 := a.new()
+	copy(m1.m, m.m)
+	return m1
+}
+
+func (a *matchArena) noMatch() *matchVec {
+	m := a.new()
+	for i := range m.m {
+		m.m[i] = -1 // no match seen; catches cases like "a(b)?c" on "ac"
+	}
+	m.ref = 1
+	return m
+}
+
+type state struct {
+	inst     *instr // next instruction to execute
+	prefixed bool   // this match began with a fixed prefix
+	match    *matchVec
+}
+
+// Append new state to to-do list.  Leftmost-longest wins so avoid
+// adding a state that's already active.  The matchVec will be inc-ref'ed
+// if it is assigned to a state.
+func (a *matchArena) addState(s []state, inst *instr, prefixed bool, match *matchVec) []state {
+	switch inst.kind {
+	case iBOT:
+		if a.atBOT {
+			s = a.addState(s, inst.next, prefixed, match)
+		}
+		return s
+	case iEOT:
+		if a.atEOT {
+			s = a.addState(s, inst.next, prefixed, match)
+		}
+		return s
+	case iBra:
+		match.m[inst.braNum] = a.pos
+		s = a.addState(s, inst.next, prefixed, match)
+		return s
+	}
+	l := len(s)
+	// States are inserted in order so it's sufficient to see if we have the same
+	// instruction; no need to see if existing match is earlier (it is).
+	for i := 0; i < l; i++ {
+		if s[i].inst == inst {
+			return s
+		}
+	}
+	s = append(s, state{inst, prefixed, match})
+	match.ref++
+	if inst.kind == iAlt {
+		s = a.addState(s, inst.left, prefixed, a.copy(match))
+		// give other branch a copy of this match vector
+		s = a.addState(s, inst.next, prefixed, a.copy(match))
+	}
+	return s
+}
+
+// input abstracts different representations of the input text. It provides
+// one-character lookahead.
+type input interface {
+	step(pos int) (rune int, width int) // advance one rune
+	canCheckPrefix() bool               // can we look ahead without losing info?
+	hasPrefix(re *Regexp) bool
+	index(re *Regexp, pos int) int
+}
+
+// inputString scans a string.
+type inputString struct {
+	str string
+}
+
+func newInputString(str string) *inputString {
+	return &inputString{str: str}
+}
+
+func (i *inputString) step(pos int) (int, int) {
+	if pos < len(i.str) {
+		return utf8.DecodeRuneInString(i.str[pos:len(i.str)])
+	}
+	return endOfText, 0
+}
+
+func (i *inputString) canCheckPrefix() bool {
+	return true
+}
+
+func (i *inputString) hasPrefix(re *Regexp) bool {
+	return strings.HasPrefix(i.str, re.prefix)
+}
+
+func (i *inputString) index(re *Regexp, pos int) int {
+	return strings.Index(i.str[pos:], re.prefix)
+}
+
+// inputBytes scans a byte slice.
+type inputBytes struct {
+	str []byte
+}
+
+func newInputBytes(str []byte) *inputBytes {
+	return &inputBytes{str: str}
+}
+
+func (i *inputBytes) step(pos int) (int, int) {
+	if pos < len(i.str) {
+		return utf8.DecodeRune(i.str[pos:len(i.str)])
+	}
+	return endOfText, 0
+}
+
+func (i *inputBytes) canCheckPrefix() bool {
+	return true
+}
+
+func (i *inputBytes) hasPrefix(re *Regexp) bool {
+	return bytes.HasPrefix(i.str, re.prefixBytes)
+}
+
+func (i *inputBytes) index(re *Regexp, pos int) int {
+	return bytes.Index(i.str[pos:], re.prefixBytes)
+}
+
+// inputReader scans a RuneReader.
+type inputReader struct {
+	r     io.RuneReader
+	atEOT bool
+	pos   int
+}
+
+func newInputReader(r io.RuneReader) *inputReader {
+	return &inputReader{r: r}
+}
+
+func (i *inputReader) step(pos int) (int, int) {
+	if !i.atEOT && pos != i.pos {
+		return endOfText, 0
+
+	}
+	r, w, err := i.r.ReadRune()
+	if err != nil {
+		i.atEOT = true
+		return endOfText, 0
+	}
+	i.pos += w
+	return r, w
+}
+
+func (i *inputReader) canCheckPrefix() bool {
+	return false
+}
+
+func (i *inputReader) hasPrefix(re *Regexp) bool {
+	return false
+}
+
+func (i *inputReader) index(re *Regexp, pos int) int {
+	return -1
+}
+
+// Search match starting from pos bytes into the input.
+func (re *Regexp) doExecute(i input, pos int) []int {
+	var s [2][]state
+	s[0] = make([]state, 0, 10)
+	s[1] = make([]state, 0, 10)
+	in, out := 0, 1
+	var final state
+	found := false
+	anchored := re.inst[0].next.kind == iBOT
+	if anchored && pos > 0 {
+		return nil
+	}
+	// fast check for initial plain substring
+	if i.canCheckPrefix() && re.prefix != "" {
+		advance := 0
+		if anchored {
+			if !i.hasPrefix(re) {
+				return nil
+			}
+		} else {
+			advance = i.index(re, pos)
+			if advance == -1 {
+				return nil
+			}
+		}
+		pos += advance
+	}
+	// We look one character ahead so we can match $, which checks whether
+	// we are at EOT.
+	nextChar, nextWidth := i.step(pos)
+	arena := &matchArena{
+		len:   2 * (re.nbra + 1),
+		pos:   pos,
+		atBOT: pos == 0,
+		atEOT: nextChar == endOfText,
+	}
+	for c, startPos := 0, pos; c != endOfText; {
+		if !found && (pos == startPos || !anchored) {
+			// prime the pump if we haven't seen a match yet
+			match := arena.noMatch()
+			match.m[0] = pos
+			s[out] = arena.addState(s[out], re.start.next, false, match)
+			arena.free(match) // if addState saved it, ref was incremented
+		} else if len(s[out]) == 0 {
+			// machine has completed
+			break
+		}
+		in, out = out, in // old out state is new in state
+		// clear out old state
+		old := s[out]
+		for _, state := range old {
+			arena.free(state.match)
+		}
+		s[out] = old[0:0] // truncate state vector
+		c = nextChar
+		thisPos := pos
+		pos += nextWidth
+		nextChar, nextWidth = i.step(pos)
+		arena.atEOT = nextChar == endOfText
+		arena.atBOT = false
+		arena.pos = pos
+		for _, st := range s[in] {
+			switch st.inst.kind {
+			case iBOT:
+			case iEOT:
+			case iChar:
+				if c == st.inst.char {
+					s[out] = arena.addState(s[out], st.inst.next, st.prefixed, st.match)
+				}
+			case iCharClass:
+				if st.inst.cclass.matches(c) {
+					s[out] = arena.addState(s[out], st.inst.next, st.prefixed, st.match)
+				}
+			case iAny:
+				if c != endOfText {
+					s[out] = arena.addState(s[out], st.inst.next, st.prefixed, st.match)
+				}
+			case iNotNL:
+				if c != endOfText && c != '\n' {
+					s[out] = arena.addState(s[out], st.inst.next, st.prefixed, st.match)
+				}
+			case iBra:
+			case iAlt:
+			case iEnd:
+				// choose leftmost longest
+				if !found || // first
+					st.match.m[0] < final.match.m[0] || // leftmost
+					(st.match.m[0] == final.match.m[0] && thisPos > final.match.m[1]) { // longest
+					if final.match != nil {
+						arena.free(final.match)
+					}
+					final = st
+					final.match.ref++
+					final.match.m[1] = thisPos
+				}
+				found = true
+			default:
+				st.inst.print()
+				panic("unknown instruction in execute")
+			}
+		}
+	}
+	if final.match == nil {
+		return nil
+	}
+	// if match found, back up start of match by width of prefix.
+	if final.prefixed && len(final.match.m) > 0 {
+		final.match.m[0] -= len(re.prefix)
+	}
+	return final.match.m
+}
+
+// LiteralPrefix returns a literal string that must begin any match
+// of the regular expression re.  It returns the boolean true if the
+// literal string comprises the entire regular expression.
+func (re *Regexp) LiteralPrefix() (prefix string, complete bool) {
+	c := make([]int, len(re.inst)-2) // minus start and end.
+	// First instruction is start; skip that.
+	i := 0
+	for inst := re.inst[0].next; inst.kind != iEnd; inst = inst.next {
+		// stop if this is not a char
+		if inst.kind != iChar {
+			return string(c[:i]), false
+		}
+		c[i] = inst.char
+		i++
+	}
+	return string(c[:i]), true
+}
+
+// MatchReader returns whether the Regexp matches the text read by the
+// RuneReader.  The return value is a boolean: true for match, false for no
+// match.
+func (re *Regexp) MatchReader(r io.RuneReader) bool {
+	return len(re.doExecute(newInputReader(r), 0)) > 0
+}
+
+// MatchString returns whether the Regexp matches the string s.
+// The return value is a boolean: true for match, false for no match.
+func (re *Regexp) MatchString(s string) bool { return len(re.doExecute(newInputString(s), 0)) > 0 }
+
+// Match returns whether the Regexp matches the byte slice b.
+// The return value is a boolean: true for match, false for no match.
+func (re *Regexp) Match(b []byte) bool { return len(re.doExecute(newInputBytes(b), 0)) > 0 }
+
+// MatchReader checks whether a textual regular expression matches the text
+// read by the RuneReader.  More complicated queries need to use Compile and
+// the full Regexp interface.
+func MatchReader(pattern string, r io.RuneReader) (matched bool, error os.Error) {
+	re, err := Compile(pattern)
+	if err != nil {
+		return false, err
+	}
+	return re.MatchReader(r), nil
+}
+
+// MatchString checks whether a textual regular expression
+// matches a string.  More complicated queries need
+// to use Compile and the full Regexp interface.
+func MatchString(pattern string, s string) (matched bool, error os.Error) {
+	re, err := Compile(pattern)
+	if err != nil {
+		return false, err
+	}
+	return re.MatchString(s), nil
+}
+
+// Match checks whether a textual regular expression
+// matches a byte slice.  More complicated queries need
+// to use Compile and the full Regexp interface.
+func Match(pattern string, b []byte) (matched bool, error os.Error) {
+	re, err := Compile(pattern)
+	if err != nil {
+		return false, err
+	}
+	return re.Match(b), nil
+}
+
+// ReplaceAllString returns a copy of src in which all matches for the Regexp
+// have been replaced by repl.  No support is provided for expressions
+// (e.g. \1 or $1) in the replacement string.
+func (re *Regexp) ReplaceAllString(src, repl string) string {
+	return re.ReplaceAllStringFunc(src, func(string) string { return repl })
+}
+
+// ReplaceAllStringFunc returns a copy of src in which all matches for the
+// Regexp have been replaced by the return value of of function repl (whose
+// first argument is the matched string).  No support is provided for
+// expressions (e.g. \1 or $1) in the replacement string.
+func (re *Regexp) ReplaceAllStringFunc(src string, repl func(string) string) string {
+	lastMatchEnd := 0 // end position of the most recent match
+	searchPos := 0    // position where we next look for a match
+	buf := new(bytes.Buffer)
+	for searchPos <= len(src) {
+		a := re.doExecute(newInputString(src), searchPos)
+		if len(a) == 0 {
+			break // no more matches
+		}
+
+		// Copy the unmatched characters before this match.
+		io.WriteString(buf, src[lastMatchEnd:a[0]])
+
+		// Now insert a copy of the replacement string, but not for a
+		// match of the empty string immediately after another match.
+		// (Otherwise, we get double replacement for patterns that
+		// match both empty and nonempty strings.)
+		if a[1] > lastMatchEnd || a[0] == 0 {
+			io.WriteString(buf, repl(src[a[0]:a[1]]))
+		}
+		lastMatchEnd = a[1]
+
+		// Advance past this match; always advance at least one character.
+		_, width := utf8.DecodeRuneInString(src[searchPos:])
+		if searchPos+width > a[1] {
+			searchPos += width
+		} else if searchPos+1 > a[1] {
+			// This clause is only needed at the end of the input
+			// string.  In that case, DecodeRuneInString returns width=0.
+			searchPos++
+		} else {
+			searchPos = a[1]
+		}
+	}
+
+	// Copy the unmatched characters after the last match.
+	io.WriteString(buf, src[lastMatchEnd:])
+
+	return buf.String()
+}
+
+// ReplaceAll returns a copy of src in which all matches for the Regexp
+// have been replaced by repl.  No support is provided for expressions
+// (e.g. \1 or $1) in the replacement text.
+func (re *Regexp) ReplaceAll(src, repl []byte) []byte {
+	return re.ReplaceAllFunc(src, func([]byte) []byte { return repl })
+}
+
+// ReplaceAllFunc returns a copy of src in which all matches for the
+// Regexp have been replaced by the return value of of function repl (whose
+// first argument is the matched []byte).  No support is provided for
+// expressions (e.g. \1 or $1) in the replacement string.
+func (re *Regexp) ReplaceAllFunc(src []byte, repl func([]byte) []byte) []byte {
+	lastMatchEnd := 0 // end position of the most recent match
+	searchPos := 0    // position where we next look for a match
+	buf := new(bytes.Buffer)
+	for searchPos <= len(src) {
+		a := re.doExecute(newInputBytes(src), searchPos)
+		if len(a) == 0 {
+			break // no more matches
+		}
+
+		// Copy the unmatched characters before this match.
+		buf.Write(src[lastMatchEnd:a[0]])
+
+		// Now insert a copy of the replacement string, but not for a
+		// match of the empty string immediately after another match.
+		// (Otherwise, we get double replacement for patterns that
+		// match both empty and nonempty strings.)
+		if a[1] > lastMatchEnd || a[0] == 0 {
+			buf.Write(repl(src[a[0]:a[1]]))
+		}
+		lastMatchEnd = a[1]
+
+		// Advance past this match; always advance at least one character.
+		_, width := utf8.DecodeRune(src[searchPos:])
+		if searchPos+width > a[1] {
+			searchPos += width
+		} else if searchPos+1 > a[1] {
+			// This clause is only needed at the end of the input
+			// string.  In that case, DecodeRuneInString returns width=0.
+			searchPos++
+		} else {
+			searchPos = a[1]
+		}
+	}
+
+	// Copy the unmatched characters after the last match.
+	buf.Write(src[lastMatchEnd:])
+
+	return buf.Bytes()
+}
+
+// QuoteMeta returns a string that quotes all regular expression metacharacters
+// inside the argument text; the returned string is a regular expression matching
+// the literal text.  For example, QuoteMeta(`[foo]`) returns `\[foo\]`.
+func QuoteMeta(s string) string {
+	b := make([]byte, 2*len(s))
+
+	// A byte loop is correct because all metacharacters are ASCII.
+	j := 0
+	for i := 0; i < len(s); i++ {
+		if special(int(s[i])) {
+			b[j] = '\\'
+			j++
+		}
+		b[j] = s[i]
+		j++
+	}
+	return string(b[0:j])
+}
+
+// Find matches in slice b if b is non-nil, otherwise find matches in string s.
+func (re *Regexp) allMatches(s string, b []byte, n int, deliver func([]int)) {
+	var end int
+	if b == nil {
+		end = len(s)
+	} else {
+		end = len(b)
+	}
+
+	for pos, i, prevMatchEnd := 0, 0, -1; i < n && pos <= end; {
+		var in input
+		if b == nil {
+			in = newInputString(s)
+		} else {
+			in = newInputBytes(b)
+		}
+		matches := re.doExecute(in, pos)
+		if len(matches) == 0 {
+			break
+		}
+
+		accept := true
+		if matches[1] == pos {
+			// We've found an empty match.
+			if matches[0] == prevMatchEnd {
+				// We don't allow an empty match right
+				// after a previous match, so ignore it.
+				accept = false
+			}
+			var width int
+			// TODO: use step()
+			if b == nil {
+				_, width = utf8.DecodeRuneInString(s[pos:end])
+			} else {
+				_, width = utf8.DecodeRune(b[pos:end])
+			}
+			if width > 0 {
+				pos += width
+			} else {
+				pos = end + 1
+			}
+		} else {
+			pos = matches[1]
+		}
+		prevMatchEnd = matches[1]
+
+		if accept {
+			deliver(matches)
+			i++
+		}
+	}
+}
+
+// Find returns a slice holding the text of the leftmost match in b of the regular expression.
+// A return value of nil indicates no match.
+func (re *Regexp) Find(b []byte) []byte {
+	a := re.doExecute(newInputBytes(b), 0)
+	if a == nil {
+		return nil
+	}
+	return b[a[0]:a[1]]
+}
+
+// FindIndex returns a two-element slice of integers defining the location of
+// the leftmost match in b of the regular expression.  The match itself is at
+// b[loc[0]:loc[1]].
+// A return value of nil indicates no match.
+func (re *Regexp) FindIndex(b []byte) (loc []int) {
+	a := re.doExecute(newInputBytes(b), 0)
+	if a == nil {
+		return nil
+	}
+	return a[0:2]
+}
+
+// FindString returns a string holding the text of the leftmost match in s of the regular
+// expression.  If there is no match, the return value is an empty string,
+// but it will also be empty if the regular expression successfully matches
+// an empty string.  Use FindStringIndex or FindStringSubmatch if it is
+// necessary to distinguish these cases.
+func (re *Regexp) FindString(s string) string {
+	a := re.doExecute(newInputString(s), 0)
+	if a == nil {
+		return ""
+	}
+	return s[a[0]:a[1]]
+}
+
+// FindStringIndex returns a two-element slice of integers defining the
+// location of the leftmost match in s of the regular expression.  The match
+// itself is at s[loc[0]:loc[1]].
+// A return value of nil indicates no match.
+func (re *Regexp) FindStringIndex(s string) []int {
+	a := re.doExecute(newInputString(s), 0)
+	if a == nil {
+		return nil
+	}
+	return a[0:2]
+}
+
+// FindReaderIndex returns a two-element slice of integers defining the
+// location of the leftmost match of the regular expression in text read from
+// the RuneReader.  The match itself is at s[loc[0]:loc[1]].  A return
+// value of nil indicates no match.
+func (re *Regexp) FindReaderIndex(r io.RuneReader) []int {
+	a := re.doExecute(newInputReader(r), 0)
+	if a == nil {
+		return nil
+	}
+	return a[0:2]
+}
+
+// FindSubmatch returns a slice of slices holding the text of the leftmost
+// match of the regular expression in b and the matches, if any, of its
+// subexpressions, as defined by the 'Submatch' descriptions in the package
+// comment.
+// A return value of nil indicates no match.
+func (re *Regexp) FindSubmatch(b []byte) [][]byte {
+	a := re.doExecute(newInputBytes(b), 0)
+	if a == nil {
+		return nil
+	}
+	ret := make([][]byte, len(a)/2)
+	for i := range ret {
+		if a[2*i] >= 0 {
+			ret[i] = b[a[2*i]:a[2*i+1]]
+		}
+	}
+	return ret
+}
+
+// FindSubmatchIndex returns a slice holding the index pairs identifying the
+// leftmost match of the regular expression in b and the matches, if any, of
+// its subexpressions, as defined by the 'Submatch' and 'Index' descriptions
+// in the package comment.
+// A return value of nil indicates no match.
+func (re *Regexp) FindSubmatchIndex(b []byte) []int {
+	return re.doExecute(newInputBytes(b), 0)
+}
+
+// FindStringSubmatch returns a slice of strings holding the text of the
+// leftmost match of the regular expression in s and the matches, if any, of
+// its subexpressions, as defined by the 'Submatch' description in the
+// package comment.
+// A return value of nil indicates no match.
+func (re *Regexp) FindStringSubmatch(s string) []string {
+	a := re.doExecute(newInputString(s), 0)
+	if a == nil {
+		return nil
+	}
+	ret := make([]string, len(a)/2)
+	for i := range ret {
+		if a[2*i] >= 0 {
+			ret[i] = s[a[2*i]:a[2*i+1]]
+		}
+	}
+	return ret
+}
+
+// FindStringSubmatchIndex returns a slice holding the index pairs
+// identifying the leftmost match of the regular expression in s and the
+// matches, if any, of its subexpressions, as defined by the 'Submatch' and
+// 'Index' descriptions in the package comment.
+// A return value of nil indicates no match.
+func (re *Regexp) FindStringSubmatchIndex(s string) []int {
+	return re.doExecute(newInputString(s), 0)
+}
+
+// FindReaderSubmatchIndex returns a slice holding the index pairs
+// identifying the leftmost match of the regular expression of text read by
+// the RuneReader, and the matches, if any, of its subexpressions, as defined
+// by the 'Submatch' and 'Index' descriptions in the package comment.  A
+// return value of nil indicates no match.
+func (re *Regexp) FindReaderSubmatchIndex(r io.RuneReader) []int {
+	return re.doExecute(newInputReader(r), 0)
+}
+
+const startSize = 10 // The size at which to start a slice in the 'All' routines.
+
+// FindAll is the 'All' version of Find; it returns a slice of all successive
+// matches of the expression, as defined by the 'All' description in the
+// package comment.
+// A return value of nil indicates no match.
+func (re *Regexp) FindAll(b []byte, n int) [][]byte {
+	if n < 0 {
+		n = len(b) + 1
+	}
+	result := make([][]byte, 0, startSize)
+	re.allMatches("", b, n, func(match []int) {
+		result = append(result, b[match[0]:match[1]])
+	})
+	if len(result) == 0 {
+		return nil
+	}
+	return result
+}
+
+// FindAllIndex is the 'All' version of FindIndex; it returns a slice of all
+// successive matches of the expression, as defined by the 'All' description
+// in the package comment.
+// A return value of nil indicates no match.
+func (re *Regexp) FindAllIndex(b []byte, n int) [][]int {
+	if n < 0 {
+		n = len(b) + 1
+	}
+	result := make([][]int, 0, startSize)
+	re.allMatches("", b, n, func(match []int) {
+		result = append(result, match[0:2])
+	})
+	if len(result) == 0 {
+		return nil
+	}
+	return result
+}
+
+// FindAllString is the 'All' version of FindString; it returns a slice of all
+// successive matches of the expression, as defined by the 'All' description
+// in the package comment.
+// A return value of nil indicates no match.
+func (re *Regexp) FindAllString(s string, n int) []string {
+	if n < 0 {
+		n = len(s) + 1
+	}
+	result := make([]string, 0, startSize)
+	re.allMatches(s, nil, n, func(match []int) {
+		result = append(result, s[match[0]:match[1]])
+	})
+	if len(result) == 0 {
+		return nil
+	}
+	return result
+}
+
+// FindAllStringIndex is the 'All' version of FindStringIndex; it returns a
+// slice of all successive matches of the expression, as defined by the 'All'
+// description in the package comment.
+// A return value of nil indicates no match.
+func (re *Regexp) FindAllStringIndex(s string, n int) [][]int {
+	if n < 0 {
+		n = len(s) + 1
+	}
+	result := make([][]int, 0, startSize)
+	re.allMatches(s, nil, n, func(match []int) {
+		result = append(result, match[0:2])
+	})
+	if len(result) == 0 {
+		return nil
+	}
+	return result
+}
+
+// FindAllSubmatch is the 'All' version of FindSubmatch; it returns a slice
+// of all successive matches of the expression, as defined by the 'All'
+// description in the package comment.
+// A return value of nil indicates no match.
+func (re *Regexp) FindAllSubmatch(b []byte, n int) [][][]byte {
+	if n < 0 {
+		n = len(b) + 1
+	}
+	result := make([][][]byte, 0, startSize)
+	re.allMatches("", b, n, func(match []int) {
+		slice := make([][]byte, len(match)/2)
+		for j := range slice {
+			if match[2*j] >= 0 {
+				slice[j] = b[match[2*j]:match[2*j+1]]
+			}
+		}
+		result = append(result, slice)
+	})
+	if len(result) == 0 {
+		return nil
+	}
+	return result
+}
+
+// FindAllSubmatchIndex is the 'All' version of FindSubmatchIndex; it returns
+// a slice of all successive matches of the expression, as defined by the
+// 'All' description in the package comment.
+// A return value of nil indicates no match.
+func (re *Regexp) FindAllSubmatchIndex(b []byte, n int) [][]int {
+	if n < 0 {
+		n = len(b) + 1
+	}
+	result := make([][]int, 0, startSize)
+	re.allMatches("", b, n, func(match []int) {
+		result = append(result, match)
+	})
+	if len(result) == 0 {
+		return nil
+	}
+	return result
+}
+
+// FindAllStringSubmatch is the 'All' version of FindStringSubmatch; it
+// returns a slice of all successive matches of the expression, as defined by
+// the 'All' description in the package comment.
+// A return value of nil indicates no match.
+func (re *Regexp) FindAllStringSubmatch(s string, n int) [][]string {
+	if n < 0 {
+		n = len(s) + 1
+	}
+	result := make([][]string, 0, startSize)
+	re.allMatches(s, nil, n, func(match []int) {
+		slice := make([]string, len(match)/2)
+		for j := range slice {
+			if match[2*j] >= 0 {
+				slice[j] = s[match[2*j]:match[2*j+1]]
+			}
+		}
+		result = append(result, slice)
+	})
+	if len(result) == 0 {
+		return nil
+	}
+	return result
+}
+
+// FindAllStringSubmatchIndex is the 'All' version of
+// FindStringSubmatchIndex; it returns a slice of all successive matches of
+// the expression, as defined by the 'All' description in the package
+// comment.
+// A return value of nil indicates no match.
+func (re *Regexp) FindAllStringSubmatchIndex(s string, n int) [][]int {
+	if n < 0 {
+		n = len(s) + 1
+	}
+	result := make([][]int, 0, startSize)
+	re.allMatches(s, nil, n, func(match []int) {
+		result = append(result, match)
+	})
+	if len(result) == 0 {
+		return nil
+	}
+	return result
+}