exp/regexp/syntax: compiled form

R=r, sam.thorogood, kevlar
CC=golang-dev, rsc
https://golang.org/cl/4636046

src/pkg/exp/regexp/syntax/Makefile

@@ -6,8 +6,10 @@ include ../../../../Make.inc
 
 TARG=exp/regexp/syntax
 GOFILES=\
+	compile.go\
 	parse.go\
 	perl_groups.go\
+	prog.go\
 	regexp.go\
 
 include ../../../../Make.pkg

src/pkg/exp/regexp/syntax/compile.go

+package syntax
+
+import (
+	"os"
+	"unicode"
+)
+
+// A patchList is a list of instruction pointers that need to be filled in (patched).
+// Because the pointers haven't been filled in yet, we can reuse their storage
+// to hold the list.  It's kind of sleazy, but works well in practice.
+// See http://swtch.com/~rsc/regexp/regexp1.html for inspiration.
+// 
+// These aren't really pointers: they're integers, so we can reinterpret them
+// this way without using package unsafe.  A value l denotes
+// p.inst[l>>1].Out (l&1==0) or .Arg (l&1==1). 
+// l == 0 denotes the empty list, okay because we start every program
+// with a fail instruction, so we'll never want to point at its output link.
+type patchList uint32
+
+func (l patchList) next(p *Prog) patchList {
+	i := &p.Inst[l>>1]
+	if l&1 == 0 {
+		return patchList(i.Out)
+	}
+	return patchList(i.Arg)
+}
+
+func (l patchList) patch(p *Prog, val uint32) {
+	for l != 0 {
+		i := &p.Inst[l>>1]
+		if l&1 == 0 {
+			l = patchList(i.Out)
+			i.Out = val
+		} else {
+			l = patchList(i.Arg)
+			i.Arg = val
+		}
+	}
+}
+
+func (l1 patchList) append(p *Prog, l2 patchList) patchList {
+	if l1 == 0 {
+		return l2
+	}
+	if l2 == 0 {
+		return l1
+	}
+
+	last := l1
+	for {
+		next := last.next(p)
+		if next == 0 {
+			break
+		}
+		last = next
+	}
+
+	i := &p.Inst[last>>1]
+	if last&1 == 0 {
+		i.Out = uint32(l2)
+	} else {
+		i.Arg = uint32(l2)
+	}
+	return l1
+}
+
+// A frag represents a compiled program fragment.
+type frag struct {
+	i   uint32    // index of first instruction
+	out patchList // where to record end instruction
+}
+
+type compiler struct {
+	p *Prog
+}
+
+// Compile compiles the regexp into a program to be executed.
+func Compile(re *Regexp) (*Prog, os.Error) {
+	var c compiler
+	c.init()
+	f := c.compile(re)
+	f.out.patch(c.p, c.inst(InstMatch).i)
+	c.p.Start = int(f.i)
+	return c.p, nil
+}
+
+func (c *compiler) init() {
+	c.p = new(Prog)
+	c.inst(InstFail)
+}
+
+var anyRuneNotNL = []int{0, '\n' - 1, '\n' - 1, unicode.MaxRune}
+var anyRune = []int{0, unicode.MaxRune}
+
+func (c *compiler) compile(re *Regexp) frag {
+	switch re.Op {
+	case OpNoMatch:
+		return c.fail()
+	case OpEmptyMatch:
+		return c.nop()
+	case OpLiteral:
+		if len(re.Rune) == 0 {
+			return c.nop()
+		}
+		var f frag
+		for j := range re.Rune {
+			f1 := c.rune(re.Rune[j : j+1])
+			if j == 0 {
+				f = f1
+			} else {
+				f = c.cat(f, f1)
+			}
+		}
+		return f
+	case OpCharClass:
+		return c.rune(re.Rune)
+	case OpAnyCharNotNL:
+		return c.rune(anyRuneNotNL)
+	case OpAnyChar:
+		return c.rune(anyRune)
+	case OpBeginLine:
+		return c.empty(EmptyBeginLine)
+	case OpEndLine:
+		return c.empty(EmptyEndLine)
+	case OpBeginText:
+		return c.empty(EmptyBeginText)
+	case OpEndText:
+		return c.empty(EmptyEndText)
+	case OpWordBoundary:
+		return c.empty(EmptyWordBoundary)
+	case OpNoWordBoundary:
+		return c.empty(EmptyNoWordBoundary)
+	case OpCapture:
+		bra := c.cap(uint32(re.Cap << 1))
+		sub := c.compile(re.Sub[0])
+		ket := c.cap(uint32(re.Cap<<1 | 1))
+		return c.cat(c.cat(bra, sub), ket)
+	case OpStar:
+		return c.star(c.compile(re.Sub[0]), re.Flags&NonGreedy != 0)
+	case OpPlus:
+		return c.plus(c.compile(re.Sub[0]), re.Flags&NonGreedy != 0)
+	case OpQuest:
+		return c.quest(c.compile(re.Sub[0]), re.Flags&NonGreedy != 0)
+	case OpConcat:
+		if len(re.Sub) == 0 {
+			return c.nop()
+		}
+		var f frag
+		for i, sub := range re.Sub {
+			if i == 0 {
+				f = c.compile(sub)
+			} else {
+				f = c.cat(f, c.compile(sub))
+			}
+		}
+		return f
+	case OpAlternate:
+		var f frag
+		for _, sub := range re.Sub {
+			f = c.alt(f, c.compile(sub))
+		}
+		return f
+	}
+	panic("regexp: unhandled case in compile")
+}
+
+func (c *compiler) inst(op InstOp) frag {
+	// TODO: impose length limit
+	f := frag{i: uint32(len(c.p.Inst))}
+	c.p.Inst = append(c.p.Inst, Inst{Op: op})
+	return f
+}
+
+func (c *compiler) nop() frag {
+	f := c.inst(InstNop)
+	f.out = patchList(f.i << 1)
+	return f
+}
+
+func (c *compiler) fail() frag {
+	return frag{}
+}
+
+func (c *compiler) cap(arg uint32) frag {
+	f := c.inst(InstCapture)
+	f.out = patchList(f.i << 1)
+	c.p.Inst[f.i].Arg = arg
+	return f
+}
+
+func (c *compiler) cat(f1, f2 frag) frag {
+	// concat of failure is failure
+	if f1.i == 0 || f2.i == 0 {
+		return frag{}
+	}
+
+	// TODO: elide nop
+
+	f1.out.patch(c.p, f2.i)
+	return frag{f1.i, f2.out}
+}
+
+func (c *compiler) alt(f1, f2 frag) frag {
+	// alt of failure is other
+	if f1.i == 0 {
+		return f2
+	}
+	if f2.i == 0 {
+		return f1
+	}
+
+	f := c.inst(InstAlt)
+	i := &c.p.Inst[f.i]
+	i.Out = f1.i
+	i.Arg = f2.i
+	f.out = f1.out.append(c.p, f2.out)
+	return f
+}
+
+func (c *compiler) quest(f1 frag, nongreedy bool) frag {
+	f := c.inst(InstAlt)
+	i := &c.p.Inst[f.i]
+	if nongreedy {
+		i.Arg = f1.i
+		f.out = patchList(f.i << 1)
+	} else {
+		i.Out = f1.i
+		f.out = patchList(f.i<<1 | 1)
+	}
+	f.out = f.out.append(c.p, f1.out)
+	return f
+}
+
+func (c *compiler) star(f1 frag, nongreedy bool) frag {
+	f := c.inst(InstAlt)
+	i := &c.p.Inst[f.i]
+	if nongreedy {
+		i.Arg = f1.i
+		f.out = patchList(f.i << 1)
+	} else {
+		i.Out = f1.i
+		f.out = patchList(f.i<<1 | 1)
+	}
+	f1.out.patch(c.p, f.i)
+	return f
+}
+
+func (c *compiler) plus(f1 frag, nongreedy bool) frag {
+	return frag{f1.i, c.star(f1, nongreedy).out}
+}
+
+func (c *compiler) empty(op EmptyOp) frag {
+	f := c.inst(InstEmptyWidth)
+	c.p.Inst[f.i].Arg = uint32(op)
+	f.out = patchList(f.i << 1)
+	return f
+}
+
+func (c *compiler) rune(rune []int) frag {
+	f := c.inst(InstRune)
+	c.p.Inst[f.i].Rune = rune
+	f.out = patchList(f.i << 1)
+	return f
+}

src/pkg/exp/regexp/syntax/prog.go

+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
+}
+
+// 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()
+}
+
+// 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))
+	}
+}

src/pkg/exp/regexp/syntax/prog_test.go

+package syntax
+
+import (
+	"testing"
+)
+
+var compileTests = []struct {
+	Regexp string
+	Prog   string
+}{
+	{"a", `  0	fail
+  1*	rune "a" -> 2
+  2	match
+`},
+	{"[A-M][n-z]", `  0	fail
+  1*	rune "AM" -> 2
+  2	rune "nz" -> 3
+  3	match
+`},
+	{"", `  0	fail
+  1*	nop -> 2
+  2	match
+`},
+	{"a?", `  0	fail
+  1	rune "a" -> 3
+  2*	alt -> 1, 3
+  3	match
+`},
+	{"a??", `  0	fail
+  1	rune "a" -> 3
+  2*	alt -> 3, 1
+  3	match
+`},
+	{"a+", `  0	fail
+  1*	rune "a" -> 2
+  2	alt -> 1, 3
+  3	match
+`},
+	{"a+?", `  0	fail
+  1*	rune "a" -> 2
+  2	alt -> 3, 1
+  3	match
+`},
+	{"a*", `  0	fail
+  1	rune "a" -> 2
+  2*	alt -> 1, 3
+  3	match
+`},
+	{"a*?", `  0	fail
+  1	rune "a" -> 2
+  2*	alt -> 3, 1
+  3	match
+`},
+	{"a+b+", `  0	fail
+  1*	rune "a" -> 2
+  2	alt -> 1, 3
+  3	rune "b" -> 4
+  4	alt -> 3, 5
+  5	match
+`},
+	{"(a+)(b+)", `  0	fail
+  1*	cap 2 -> 2
+  2	rune "a" -> 3
+  3	alt -> 2, 4
+  4	cap 3 -> 5
+  5	cap 4 -> 6
+  6	rune "b" -> 7
+  7	alt -> 6, 8
+  8	cap 5 -> 9
+  9	match
+`},
+	{"a+|b+", `  0	fail
+  1	rune "a" -> 2
+  2	alt -> 1, 6
+  3	rune "b" -> 4
+  4	alt -> 3, 6
+  5*	alt -> 1, 3
+  6	match
+`},
+}
+
+func TestCompile(t *testing.T) {
+	for _, tt := range compileTests {
+		re, _ := Parse(tt.Regexp, Perl)
+		p, _ := Compile(re)
+		s := p.String()
+		if s != tt.Prog {
+			t.Errorf("compiled %#q:\n--- have\n%s---\n--- want\n%s---", tt.Regexp, s, tt.Prog)
+		}
+	}
+}