unicode/norm/composition.go - text - Git at Google

 // Copyright 2011 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 norm

 import "unicode/utf8"

 const (
 	maxNonStarters = 30
 	// The maximum number of characters needed for a buffer is
 	// maxNonStarters + 1 for the starter + 1 for the GCJ
 	maxBufferSize    = maxNonStarters + 2
 	maxNFCExpansion  = 3  // NFC(0x1D160)
 	maxNFKCExpansion = 18 // NFKC(0xFDFA)

 	maxByteBufferSize = utf8.UTFMax * maxBufferSize // 128
 )

 // ssState is used for reporting the segment state after inserting a rune.
 // It is returned by streamSafe.next.
 type ssState int

 const (
 	// Indicates a rune was successfully added to the segment.
 	ssSuccess ssState = iota
 	// Indicates a rune starts a new segment and should not be added.
 	ssStarter
 	// Indicates a rune caused a segment overflow and a CGJ should be inserted.
 	ssOverflow
 )

 // streamSafe implements the policy of when a CGJ should be inserted.
 type streamSafe uint8

 // mkStreamSafe is a shorthand for declaring a streamSafe var and calling
 // first on it.
 func mkStreamSafe(p Properties) streamSafe {
 	return streamSafe(p.nTrailingNonStarters())
 }

 // first inserts the first rune of a segment.
 func (ss *streamSafe) first(p Properties) {
 	if *ss != 0 {
 		panic("!= 0")
 	}
 	*ss = streamSafe(p.nTrailingNonStarters())
 }

 // insert returns a ssState value to indicate whether a rune represented by p
 // can be inserted.
 func (ss *streamSafe) next(p Properties) ssState {
 	if *ss > maxNonStarters {
 		panic("streamSafe was not reset")
 	}
 	n := p.nLeadingNonStarters()
 	if *ss += streamSafe(n); *ss > maxNonStarters {
 		*ss = 0
 		return ssOverflow
 	}
 	// The Stream-Safe Text Processing prescribes that the counting can stop
 	// as soon as a starter is encountered. However, there are some starters,
 	// like Jamo V and T, that can combine with other runes, leaving their
 	// successive non-starters appended to the previous, possibly causing an
 	// overflow. We will therefore consider any rune with a non-zero nLead to
 	// be a non-starter. Note that it always hold that if nLead > 0 then
 	// nLead == nTrail.
 	if n == 0 {
 		*ss = 0
 		return ssStarter
 	}
 	return ssSuccess
 }

 // backwards is used for checking for overflow and segment starts
 // when traversing a string backwards. Users do not need to call first
 // for the first rune. The state of the streamSafe retains the count of
 // the non-starters loaded.
 func (ss *streamSafe) backwards(p Properties) ssState {
 	if *ss > maxNonStarters {
 		panic("streamSafe was not reset")
 	}
 	c := *ss + streamSafe(p.nTrailingNonStarters())
 	if c > maxNonStarters {
 		return ssOverflow
 	}
 	*ss = c
 	if p.nLeadingNonStarters() == 0 {
 		return ssStarter
 	}
 	return ssSuccess
 }

 func (ss streamSafe) isMax() bool {
 	return ss == maxNonStarters
 }

 // GraphemeJoiner is inserted after maxNonStarters non-starter runes.
 const GraphemeJoiner = "\u034F"

 // reorderBuffer is used to normalize a single segment.  Characters inserted with
 // insert are decomposed and reordered based on CCC. The compose method can
 // be used to recombine characters.  Note that the byte buffer does not hold
 // the UTF-8 characters in order.  Only the rune array is maintained in sorted
 // order. flush writes the resulting segment to a byte array.
 type reorderBuffer struct {
 	rune  [maxBufferSize]Properties // Per character info.
 	byte  [maxByteBufferSize]byte   // UTF-8 buffer. Referenced by runeInfo.pos.
 	nbyte uint8                     // Number or bytes.
 	ss    streamSafe                // For limiting length of non-starter sequence.
 	nrune int                       // Number of runeInfos.
 	f     formInfo

 	src      input
 	nsrc     int
 	tmpBytes input

 	out    []byte
 	flushF func(*reorderBuffer) bool
 }

 func (rb *reorderBuffer) init(f Form, src []byte) {
 	rb.f = *formTable[f]
 	rb.src.setBytes(src)
 	rb.nsrc = len(src)
 	rb.ss = 0
 }

 func (rb *reorderBuffer) initString(f Form, src string) {
 	rb.f = *formTable[f]
 	rb.src.setString(src)
 	rb.nsrc = len(src)
 	rb.ss = 0
 }

 func (rb *reorderBuffer) setFlusher(out []byte, f func(*reorderBuffer) bool) {
 	rb.out = out
 	rb.flushF = f
 }

 // reset discards all characters from the buffer.
 func (rb *reorderBuffer) reset() {
 	rb.nrune = 0
 	rb.nbyte = 0
 	rb.ss = 0
 }

 func (rb *reorderBuffer) doFlush() bool {
 	if rb.f.composing {
 		rb.compose()
 	}
 	res := rb.flushF(rb)
 	rb.reset()
 	return res
 }

 // appendFlush appends the normalized segment to rb.out.
 func appendFlush(rb *reorderBuffer) bool {
 	for i := 0; i < rb.nrune; i++ {
 		start := rb.rune[i].pos
 		end := start + rb.rune[i].size
 		rb.out = append(rb.out, rb.byte[start:end]...)
 	}
 	return true
 }

 // flush appends the normalized segment to out and resets rb.
 func (rb *reorderBuffer) flush(out []byte) []byte {
 	for i := 0; i < rb.nrune; i++ {
 		start := rb.rune[i].pos
 		end := start + rb.rune[i].size
 		out = append(out, rb.byte[start:end]...)
 	}
 	rb.reset()
 	return out
 }

 // flushCopy copies the normalized segment to buf and resets rb.
 // It returns the number of bytes written to buf.
 func (rb *reorderBuffer) flushCopy(buf []byte) int {
 	p := 0
 	for i := 0; i < rb.nrune; i++ {
 		runep := rb.rune[i]
 		p += copy(buf[p:], rb.byte[runep.pos:runep.pos+runep.size])
 	}
 	rb.reset()
 	return p
 }

 // insertOrdered inserts a rune in the buffer, ordered by Canonical Combining Class.
 // It returns false if the buffer is not large enough to hold the rune.
 // It is used internally by insert and insertString only.
 func (rb *reorderBuffer) insertOrdered(info Properties) {
 	n := rb.nrune
 	b := rb.rune[:]
 	cc := info.ccc
 	if cc > 0 {
 		// Find insertion position + move elements to make room.
 		for ; n > 0; n-- {
 			if b[n-1].ccc <= cc {
 				break
 			}
 			b[n] = b[n-1]
 		}
 	}
 	rb.nrune += 1
 	pos := uint8(rb.nbyte)
 	rb.nbyte += utf8.UTFMax
 	info.pos = pos
 	b[n] = info
 }

 // insertErr is an error code returned by insert. Using this type instead
 // of error improves performance up to 20% for many of the benchmarks.
 type insertErr int

 const (
 	iSuccess insertErr = -iota
 	iShortDst
 	iShortSrc
 )

 // insertFlush inserts the given rune in the buffer ordered by CCC.
 // If a decomposition with multiple segments are encountered, they leading
 // ones are flushed.
 // It returns a non-zero error code if the rune was not inserted.
 func (rb *reorderBuffer) insertFlush(src input, i int, info Properties) insertErr {
 	if rune := src.hangul(i); rune != 0 {
 		rb.decomposeHangul(rune)
 		return iSuccess
 	}
 	if info.hasDecomposition() {
 		return rb.insertDecomposed(info.Decomposition())
 	}
 	rb.insertSingle(src, i, info)
 	return iSuccess
 }

 // insertUnsafe inserts the given rune in the buffer ordered by CCC.
 // It is assumed there is sufficient space to hold the runes. It is the
 // responsibility of the caller to ensure this. This can be done by checking
 // the state returned by the streamSafe type.
 func (rb *reorderBuffer) insertUnsafe(src input, i int, info Properties) {
 	if rune := src.hangul(i); rune != 0 {
 		rb.decomposeHangul(rune)
 	}
 	if info.hasDecomposition() {
 		// TODO: inline.
 		rb.insertDecomposed(info.Decomposition())
 	} else {
 		rb.insertSingle(src, i, info)
 	}
 }

 // insertDecomposed inserts an entry in to the reorderBuffer for each rune
 // in dcomp. dcomp must be a sequence of decomposed UTF-8-encoded runes.
 // It flushes the buffer on each new segment start.
 func (rb *reorderBuffer) insertDecomposed(dcomp []byte) insertErr {
 	rb.tmpBytes.setBytes(dcomp)
 	for i := 0; i < len(dcomp); {
 		info := rb.f.info(rb.tmpBytes, i)
 		if info.BoundaryBefore() && rb.nrune > 0 && !rb.doFlush() {
 			return iShortDst
 		}
 		i += copy(rb.byte[rb.nbyte:], dcomp[i:i+int(info.size)])
 		rb.insertOrdered(info)
 	}
 	return iSuccess
 }

 // insertSingle inserts an entry in the reorderBuffer for the rune at
 // position i. info is the runeInfo for the rune at position i.
 func (rb *reorderBuffer) insertSingle(src input, i int, info Properties) {
 	src.copySlice(rb.byte[rb.nbyte:], i, i+int(info.size))
 	rb.insertOrdered(info)
 }

 // insertCGJ inserts a Combining Grapheme Joiner (0x034f) into rb.
 func (rb *reorderBuffer) insertCGJ() {
 	rb.insertSingle(input{str: GraphemeJoiner}, 0, Properties{size: uint8(len(GraphemeJoiner))})
 }

 // appendRune inserts a rune at the end of the buffer. It is used for Hangul.
 func (rb *reorderBuffer) appendRune(r rune) {
 	bn := rb.nbyte
 	sz := utf8.EncodeRune(rb.byte[bn:], rune(r))
 	rb.nbyte += utf8.UTFMax
 	rb.rune[rb.nrune] = Properties{pos: bn, size: uint8(sz)}
 	rb.nrune++
 }

 // assignRune sets a rune at position pos. It is used for Hangul and recomposition.
 func (rb *reorderBuffer) assignRune(pos int, r rune) {
 	bn := rb.rune[pos].pos
 	sz := utf8.EncodeRune(rb.byte[bn:], rune(r))
 	rb.rune[pos] = Properties{pos: bn, size: uint8(sz)}
 }

 // runeAt returns the rune at position n. It is used for Hangul and recomposition.
 func (rb *reorderBuffer) runeAt(n int) rune {
 	inf := rb.rune[n]
 	r, _ := utf8.DecodeRune(rb.byte[inf.pos : inf.pos+inf.size])
 	return r
 }

 // bytesAt returns the UTF-8 encoding of the rune at position n.
 // It is used for Hangul and recomposition.
 func (rb *reorderBuffer) bytesAt(n int) []byte {
 	inf := rb.rune[n]
 	return rb.byte[inf.pos : int(inf.pos)+int(inf.size)]
 }

 // For Hangul we combine algorithmically, instead of using tables.
 const (
 	hangulBase  = 0xAC00 // UTF-8(hangulBase) -> EA B0 80
 	hangulBase0 = 0xEA
 	hangulBase1 = 0xB0
 	hangulBase2 = 0x80

 	hangulEnd  = hangulBase + jamoLVTCount // UTF-8(0xD7A4) -> ED 9E A4
 	hangulEnd0 = 0xED
 	hangulEnd1 = 0x9E
 	hangulEnd2 = 0xA4

 	jamoLBase  = 0x1100 // UTF-8(jamoLBase) -> E1 84 00
 	jamoLBase0 = 0xE1
 	jamoLBase1 = 0x84
 	jamoLEnd   = 0x1113
 	jamoVBase  = 0x1161
 	jamoVEnd   = 0x1176
 	jamoTBase  = 0x11A7
 	jamoTEnd   = 0x11C3

 	jamoTCount   = 28
 	jamoVCount   = 21
 	jamoVTCount  = 21 * 28
 	jamoLVTCount = 19 * 21 * 28
 )

 const hangulUTF8Size = 3

 func isHangul(b []byte) bool {
 	if len(b) < hangulUTF8Size {
 		return false
 	}
 	b0 := b[0]
 	if b0 < hangulBase0 {
 		return false
 	}
 	b1 := b[1]
 	switch {
 	case b0 == hangulBase0:
 		return b1 >= hangulBase1
 	case b0 < hangulEnd0:
 		return true
 	case b0 > hangulEnd0:
 		return false
 	case b1 < hangulEnd1:
 		return true
 	}
 	return b1 == hangulEnd1 && b[2] < hangulEnd2
 }

 func isHangulString(b string) bool {
 	if len(b) < hangulUTF8Size {
 		return false
 	}
 	b0 := b[0]
 	if b0 < hangulBase0 {
 		return false
 	}
 	b1 := b[1]
 	switch {
 	case b0 == hangulBase0:
 		return b1 >= hangulBase1
 	case b0 < hangulEnd0:
 		return true
 	case b0 > hangulEnd0:
 		return false
 	case b1 < hangulEnd1:
 		return true
 	}
 	return b1 == hangulEnd1 && b[2] < hangulEnd2
 }

 // Caller must ensure len(b) >= 2.
 func isJamoVT(b []byte) bool {
 	// True if (rune & 0xff00) == jamoLBase
 	return b[0] == jamoLBase0 && (b[1]&0xFC) == jamoLBase1
 }

 func isHangulWithoutJamoT(b []byte) bool {
 	c, _ := utf8.DecodeRune(b)
 	c -= hangulBase
 	return c < jamoLVTCount && c%jamoTCount == 0
 }

 // decomposeHangul writes the decomposed Hangul to buf and returns the number
 // of bytes written.  len(buf) should be at least 9.
 func decomposeHangul(buf []byte, r rune) int {
 	const JamoUTF8Len = 3
 	r -= hangulBase
 	x := r % jamoTCount
 	r /= jamoTCount
 	utf8.EncodeRune(buf, jamoLBase+r/jamoVCount)
 	utf8.EncodeRune(buf[JamoUTF8Len:], jamoVBase+r%jamoVCount)
 	if x != 0 {
 		utf8.EncodeRune(buf[2*JamoUTF8Len:], jamoTBase+x)
 		return 3 * JamoUTF8Len
 	}
 	return 2 * JamoUTF8Len
 }

 // decomposeHangul algorithmically decomposes a Hangul rune into
 // its Jamo components.
 // See http://unicode.org/reports/tr15/#Hangul for details on decomposing Hangul.
 func (rb *reorderBuffer) decomposeHangul(r rune) {
 	r -= hangulBase
 	x := r % jamoTCount
 	r /= jamoTCount
 	rb.appendRune(jamoLBase + r/jamoVCount)
 	rb.appendRune(jamoVBase + r%jamoVCount)
 	if x != 0 {
 		rb.appendRune(jamoTBase + x)
 	}
 }

 // combineHangul algorithmically combines Jamo character components into Hangul.
 // See http://unicode.org/reports/tr15/#Hangul for details on combining Hangul.
 func (rb *reorderBuffer) combineHangul(s, i, k int) {
 	b := rb.rune[:]
 	bn := rb.nrune
 	for ; i < bn; i++ {
 		cccB := b[k-1].ccc
 		cccC := b[i].ccc
 		if cccB == 0 {
 			s = k - 1
 		}
 		if s != k-1 && cccB >= cccC {
 			// b[i] is blocked by greater-equal cccX below it
 			b[k] = b[i]
 			k++
 		} else {
 			l := rb.runeAt(s) // also used to compare to hangulBase
 			v := rb.runeAt(i) // also used to compare to jamoT
 			switch {
 			case jamoLBase <= l && l < jamoLEnd &&
 				jamoVBase <= v && v < jamoVEnd:
 				// 11xx plus 116x to LV
 				rb.assignRune(s, hangulBase+
 					(l-jamoLBase)*jamoVTCount+(v-jamoVBase)*jamoTCount)
 			case hangulBase <= l && l < hangulEnd &&
 				jamoTBase < v && v < jamoTEnd &&
 				((l-hangulBase)%jamoTCount) == 0:
 				// ACxx plus 11Ax to LVT
 				rb.assignRune(s, l+v-jamoTBase)
 			default:
 				b[k] = b[i]
 				k++
 			}
 		}
 	}
 	rb.nrune = k
 }

 // compose recombines the runes in the buffer.
 // It should only be used to recompose a single segment, as it will not
 // handle alternations between Hangul and non-Hangul characters correctly.
 func (rb *reorderBuffer) compose() {
 	// UAX #15, section X5 , including Corrigendum #5
 	// "In any character sequence beginning with starter S, a character C is
 	//  blocked from S if and only if there is some character B between S
 	//  and C, and either B is a starter or it has the same or higher
 	//  combining class as C."
 	bn := rb.nrune
 	if bn == 0 {
 		return
 	}
 	k := 1
 	b := rb.rune[:]
 	for s, i := 0, 1; i < bn; i++ {
 		if isJamoVT(rb.bytesAt(i)) {
 			// Redo from start in Hangul mode. Necessary to support
 			// U+320E..U+321E in NFKC mode.
 			rb.combineHangul(s, i, k)
 			return
 		}
 		ii := b[i]
 		// We can only use combineForward as a filter if we later
 		// get the info for the combined character. This is more
 		// expensive than using the filter. Using combinesBackward()
 		// is safe.
 		if ii.combinesBackward() {
 			cccB := b[k-1].ccc
 			cccC := ii.ccc
 			blocked := false // b[i] blocked by starter or greater or equal CCC?
 			if cccB == 0 {
 				s = k - 1
 			} else {
 				blocked = s != k-1 && cccB >= cccC
 			}
 			if !blocked {
 				combined := combine(rb.runeAt(s), rb.runeAt(i))
 				if combined != 0 {
 					rb.assignRune(s, combined)
 					continue
 				}
 			}
 		}
 		b[k] = b[i]
 		k++
 	}
 	rb.nrune = k
 }
	// Copyright 2011 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 norm

	import "unicode/utf8"

	const (
	maxNonStarters = 30
	// The maximum number of characters needed for a buffer is
	// maxNonStarters + 1 for the starter + 1 for the GCJ
	maxBufferSize = maxNonStarters + 2
	maxNFCExpansion = 3 // NFC(0x1D160)
	maxNFKCExpansion = 18 // NFKC(0xFDFA)

	maxByteBufferSize = utf8.UTFMax * maxBufferSize // 128
	)

	// ssState is used for reporting the segment state after inserting a rune.
	// It is returned by streamSafe.next.
	type ssState int

	const (
	// Indicates a rune was successfully added to the segment.
	ssSuccess ssState = iota
	// Indicates a rune starts a new segment and should not be added.
	ssStarter
	// Indicates a rune caused a segment overflow and a CGJ should be inserted.
	ssOverflow
	)

	// streamSafe implements the policy of when a CGJ should be inserted.
	type streamSafe uint8

	// mkStreamSafe is a shorthand for declaring a streamSafe var and calling
	// first on it.
	func mkStreamSafe(p Properties) streamSafe {
	return streamSafe(p.nTrailingNonStarters())
	}

	// first inserts the first rune of a segment.
	func (ss *streamSafe) first(p Properties) {
	if *ss != 0 {
	panic("!= 0")
	}
	*ss = streamSafe(p.nTrailingNonStarters())
	}

	// insert returns a ssState value to indicate whether a rune represented by p
	// can be inserted.
	func (ss *streamSafe) next(p Properties) ssState {
	if *ss > maxNonStarters {
	panic("streamSafe was not reset")
	}
	n := p.nLeadingNonStarters()
	if ss += streamSafe(n); ss > maxNonStarters {
	*ss = 0
	return ssOverflow
	}
	// The Stream-Safe Text Processing prescribes that the counting can stop
	// as soon as a starter is encountered. However, there are some starters,
	// like Jamo V and T, that can combine with other runes, leaving their
	// successive non-starters appended to the previous, possibly causing an
	// overflow. We will therefore consider any rune with a non-zero nLead to
	// be a non-starter. Note that it always hold that if nLead > 0 then
	// nLead == nTrail.
	if n == 0 {
	*ss = 0
	return ssStarter
	}
	return ssSuccess
	}

	// backwards is used for checking for overflow and segment starts
	// when traversing a string backwards. Users do not need to call first
	// for the first rune. The state of the streamSafe retains the count of
	// the non-starters loaded.
	func (ss *streamSafe) backwards(p Properties) ssState {
	if *ss > maxNonStarters {
	panic("streamSafe was not reset")
	}
	c := *ss + streamSafe(p.nTrailingNonStarters())
	if c > maxNonStarters {
	return ssOverflow
	}
	*ss = c
	if p.nLeadingNonStarters() == 0 {
	return ssStarter
	}
	return ssSuccess
	}

	func (ss streamSafe) isMax() bool {
	return ss == maxNonStarters
	}

	// GraphemeJoiner is inserted after maxNonStarters non-starter runes.
	const GraphemeJoiner = "\u034F"

	// reorderBuffer is used to normalize a single segment. Characters inserted with
	// insert are decomposed and reordered based on CCC. The compose method can
	// be used to recombine characters. Note that the byte buffer does not hold
	// the UTF-8 characters in order. Only the rune array is maintained in sorted
	// order. flush writes the resulting segment to a byte array.
	type reorderBuffer struct {
	rune [maxBufferSize]Properties // Per character info.
	byte [maxByteBufferSize]byte // UTF-8 buffer. Referenced by runeInfo.pos.
	nbyte uint8 // Number or bytes.
	ss streamSafe // For limiting length of non-starter sequence.
	nrune int // Number of runeInfos.
	f formInfo

	src input
	nsrc int
	tmpBytes input

	out []byte
	flushF func(*reorderBuffer) bool
	}

	func (rb *reorderBuffer) init(f Form, src []byte) {
	rb.f = *formTable[f]
	rb.src.setBytes(src)
	rb.nsrc = len(src)
	rb.ss = 0
	}

	func (rb *reorderBuffer) initString(f Form, src string) {
	rb.f = *formTable[f]
	rb.src.setString(src)
	rb.nsrc = len(src)
	rb.ss = 0
	}

	func (rb reorderBuffer) setFlusher(out []byte, f func(reorderBuffer) bool) {
	rb.out = out
	rb.flushF = f
	}

	// reset discards all characters from the buffer.
	func (rb *reorderBuffer) reset() {
	rb.nrune = 0
	rb.nbyte = 0
	rb.ss = 0
	}

	func (rb *reorderBuffer) doFlush() bool {
	if rb.f.composing {
	rb.compose()
	}
	res := rb.flushF(rb)
	rb.reset()
	return res
	}

	// appendFlush appends the normalized segment to rb.out.
	func appendFlush(rb *reorderBuffer) bool {
	for i := 0; i < rb.nrune; i++ {
	start := rb.rune[i].pos
	end := start + rb.rune[i].size
	rb.out = append(rb.out, rb.byte[start:end]...)
	}
	return true
	}

	// flush appends the normalized segment to out and resets rb.
	func (rb *reorderBuffer) flush(out []byte) []byte {
	for i := 0; i < rb.nrune; i++ {
	start := rb.rune[i].pos
	end := start + rb.rune[i].size
	out = append(out, rb.byte[start:end]...)
	}
	rb.reset()
	return out
	}

	// flushCopy copies the normalized segment to buf and resets rb.
	// It returns the number of bytes written to buf.
	func (rb *reorderBuffer) flushCopy(buf []byte) int {
	p := 0
	for i := 0; i < rb.nrune; i++ {
	runep := rb.rune[i]
	p += copy(buf[p:], rb.byte[runep.pos:runep.pos+runep.size])
	}
	rb.reset()
	return p
	}

	// insertOrdered inserts a rune in the buffer, ordered by Canonical Combining Class.
	// It returns false if the buffer is not large enough to hold the rune.
	// It is used internally by insert and insertString only.
	func (rb *reorderBuffer) insertOrdered(info Properties) {
	n := rb.nrune
	b := rb.rune[:]
	cc := info.ccc
	if cc > 0 {
	// Find insertion position + move elements to make room.
	for ; n > 0; n-- {
	if b[n-1].ccc <= cc {
	break
	}
	b[n] = b[n-1]
	}
	}
	rb.nrune += 1
	pos := uint8(rb.nbyte)
	rb.nbyte += utf8.UTFMax
	info.pos = pos
	b[n] = info
	}

	// insertErr is an error code returned by insert. Using this type instead
	// of error improves performance up to 20% for many of the benchmarks.
	type insertErr int

	const (
	iSuccess insertErr = -iota
	iShortDst
	iShortSrc
	)

	// insertFlush inserts the given rune in the buffer ordered by CCC.
	// If a decomposition with multiple segments are encountered, they leading
	// ones are flushed.
	// It returns a non-zero error code if the rune was not inserted.
	func (rb *reorderBuffer) insertFlush(src input, i int, info Properties) insertErr {
	if rune := src.hangul(i); rune != 0 {
	rb.decomposeHangul(rune)
	return iSuccess
	}
	if info.hasDecomposition() {
	return rb.insertDecomposed(info.Decomposition())
	}
	rb.insertSingle(src, i, info)
	return iSuccess
	}

	// insertUnsafe inserts the given rune in the buffer ordered by CCC.
	// It is assumed there is sufficient space to hold the runes. It is the
	// responsibility of the caller to ensure this. This can be done by checking
	// the state returned by the streamSafe type.
	func (rb *reorderBuffer) insertUnsafe(src input, i int, info Properties) {
	if rune := src.hangul(i); rune != 0 {
	rb.decomposeHangul(rune)
	}
	if info.hasDecomposition() {
	// TODO: inline.
	rb.insertDecomposed(info.Decomposition())
	} else {
	rb.insertSingle(src, i, info)
	}
	}

	// insertDecomposed inserts an entry in to the reorderBuffer for each rune
	// in dcomp. dcomp must be a sequence of decomposed UTF-8-encoded runes.
	// It flushes the buffer on each new segment start.
	func (rb *reorderBuffer) insertDecomposed(dcomp []byte) insertErr {
	rb.tmpBytes.setBytes(dcomp)
	for i := 0; i < len(dcomp); {
	info := rb.f.info(rb.tmpBytes, i)
	if info.BoundaryBefore() && rb.nrune > 0 && !rb.doFlush() {
	return iShortDst
	}
	i += copy(rb.byte[rb.nbyte:], dcomp[i:i+int(info.size)])
	rb.insertOrdered(info)
	}
	return iSuccess
	}

	// insertSingle inserts an entry in the reorderBuffer for the rune at
	// position i. info is the runeInfo for the rune at position i.
	func (rb *reorderBuffer) insertSingle(src input, i int, info Properties) {
	src.copySlice(rb.byte[rb.nbyte:], i, i+int(info.size))
	rb.insertOrdered(info)
	}

	// insertCGJ inserts a Combining Grapheme Joiner (0x034f) into rb.
	func (rb *reorderBuffer) insertCGJ() {
	rb.insertSingle(input{str: GraphemeJoiner}, 0, Properties{size: uint8(len(GraphemeJoiner))})
	}

	// appendRune inserts a rune at the end of the buffer. It is used for Hangul.
	func (rb *reorderBuffer) appendRune(r rune) {
	bn := rb.nbyte
	sz := utf8.EncodeRune(rb.byte[bn:], rune(r))
	rb.nbyte += utf8.UTFMax
	rb.rune[rb.nrune] = Properties{pos: bn, size: uint8(sz)}
	rb.nrune++
	}

	// assignRune sets a rune at position pos. It is used for Hangul and recomposition.
	func (rb *reorderBuffer) assignRune(pos int, r rune) {
	bn := rb.rune[pos].pos
	sz := utf8.EncodeRune(rb.byte[bn:], rune(r))
	rb.rune[pos] = Properties{pos: bn, size: uint8(sz)}
	}

	// runeAt returns the rune at position n. It is used for Hangul and recomposition.
	func (rb *reorderBuffer) runeAt(n int) rune {
	inf := rb.rune[n]
	r, _ := utf8.DecodeRune(rb.byte[inf.pos : inf.pos+inf.size])
	return r
	}

	// bytesAt returns the UTF-8 encoding of the rune at position n.
	// It is used for Hangul and recomposition.
	func (rb *reorderBuffer) bytesAt(n int) []byte {
	inf := rb.rune[n]
	return rb.byte[inf.pos : int(inf.pos)+int(inf.size)]
	}

	// For Hangul we combine algorithmically, instead of using tables.
	const (
	hangulBase = 0xAC00 // UTF-8(hangulBase) -> EA B0 80
	hangulBase0 = 0xEA
	hangulBase1 = 0xB0
	hangulBase2 = 0x80

	hangulEnd = hangulBase + jamoLVTCount // UTF-8(0xD7A4) -> ED 9E A4
	hangulEnd0 = 0xED
	hangulEnd1 = 0x9E
	hangulEnd2 = 0xA4

	jamoLBase = 0x1100 // UTF-8(jamoLBase) -> E1 84 00
	jamoLBase0 = 0xE1
	jamoLBase1 = 0x84
	jamoLEnd = 0x1113
	jamoVBase = 0x1161
	jamoVEnd = 0x1176
	jamoTBase = 0x11A7
	jamoTEnd = 0x11C3

	jamoTCount = 28
	jamoVCount = 21
	jamoVTCount = 21 * 28
	jamoLVTCount = 19 * 21 * 28
	)

	const hangulUTF8Size = 3

	func isHangul(b []byte) bool {
	if len(b) < hangulUTF8Size {
	return false
	}
	b0 := b[0]
	if b0 < hangulBase0 {
	return false
	}
	b1 := b[1]
	switch {
	case b0 == hangulBase0:
	return b1 >= hangulBase1
	case b0 < hangulEnd0:
	return true
	case b0 > hangulEnd0:
	return false
	case b1 < hangulEnd1:
	return true
	}
	return b1 == hangulEnd1 && b[2] < hangulEnd2
	}

	func isHangulString(b string) bool {
	if len(b) < hangulUTF8Size {
	return false
	}
	b0 := b[0]
	if b0 < hangulBase0 {
	return false
	}
	b1 := b[1]
	switch {
	case b0 == hangulBase0:
	return b1 >= hangulBase1
	case b0 < hangulEnd0:
	return true
	case b0 > hangulEnd0:
	return false
	case b1 < hangulEnd1:
	return true
	}
	return b1 == hangulEnd1 && b[2] < hangulEnd2
	}

	// Caller must ensure len(b) >= 2.
	func isJamoVT(b []byte) bool {
	// True if (rune & 0xff00) == jamoLBase
	return b[0] == jamoLBase0 && (b[1]&0xFC) == jamoLBase1
	}

	func isHangulWithoutJamoT(b []byte) bool {
	c, _ := utf8.DecodeRune(b)
	c -= hangulBase
	return c < jamoLVTCount && c%jamoTCount == 0
	}

	// decomposeHangul writes the decomposed Hangul to buf and returns the number
	// of bytes written. len(buf) should be at least 9.
	func decomposeHangul(buf []byte, r rune) int {
	const JamoUTF8Len = 3
	r -= hangulBase
	x := r % jamoTCount
	r /= jamoTCount
	utf8.EncodeRune(buf, jamoLBase+r/jamoVCount)
	utf8.EncodeRune(buf[JamoUTF8Len:], jamoVBase+r%jamoVCount)
	if x != 0 {
	utf8.EncodeRune(buf[2*JamoUTF8Len:], jamoTBase+x)
	return 3 * JamoUTF8Len
	}
	return 2 * JamoUTF8Len
	}

	// decomposeHangul algorithmically decomposes a Hangul rune into
	// its Jamo components.
	// See http://unicode.org/reports/tr15/#Hangul for details on decomposing Hangul.
	func (rb *reorderBuffer) decomposeHangul(r rune) {
	r -= hangulBase
	x := r % jamoTCount
	r /= jamoTCount
	rb.appendRune(jamoLBase + r/jamoVCount)
	rb.appendRune(jamoVBase + r%jamoVCount)
	if x != 0 {
	rb.appendRune(jamoTBase + x)
	}
	}

	// combineHangul algorithmically combines Jamo character components into Hangul.
	// See http://unicode.org/reports/tr15/#Hangul for details on combining Hangul.
	func (rb *reorderBuffer) combineHangul(s, i, k int) {
	b := rb.rune[:]
	bn := rb.nrune
	for ; i < bn; i++ {
	cccB := b[k-1].ccc
	cccC := b[i].ccc
	if cccB == 0 {
	s = k - 1
	}
	if s != k-1 && cccB >= cccC {
	// b[i] is blocked by greater-equal cccX below it
	b[k] = b[i]
	k++
	} else {
	l := rb.runeAt(s) // also used to compare to hangulBase
	v := rb.runeAt(i) // also used to compare to jamoT
	switch {
	case jamoLBase <= l && l < jamoLEnd &&
	jamoVBase <= v && v < jamoVEnd:
	// 11xx plus 116x to LV
	rb.assignRune(s, hangulBase+
	(l-jamoLBase)jamoVTCount+(v-jamoVBase)jamoTCount)
	case hangulBase <= l && l < hangulEnd &&
	jamoTBase < v && v < jamoTEnd &&
	((l-hangulBase)%jamoTCount) == 0:
	// ACxx plus 11Ax to LVT
	rb.assignRune(s, l+v-jamoTBase)
	default:
	b[k] = b[i]
	k++
	}
	}
	}
	rb.nrune = k
	}

	// compose recombines the runes in the buffer.
	// It should only be used to recompose a single segment, as it will not
	// handle alternations between Hangul and non-Hangul characters correctly.
	func (rb *reorderBuffer) compose() {
	// UAX #15, section X5 , including Corrigendum #5
	// "In any character sequence beginning with starter S, a character C is
	// blocked from S if and only if there is some character B between S
	// and C, and either B is a starter or it has the same or higher
	// combining class as C."
	bn := rb.nrune
	if bn == 0 {
	return
	}
	k := 1
	b := rb.rune[:]
	for s, i := 0, 1; i < bn; i++ {
	if isJamoVT(rb.bytesAt(i)) {
	// Redo from start in Hangul mode. Necessary to support
	// U+320E..U+321E in NFKC mode.
	rb.combineHangul(s, i, k)
	return
	}
	ii := b[i]
	// We can only use combineForward as a filter if we later
	// get the info for the combined character. This is more
	// expensive than using the filter. Using combinesBackward()
	// is safe.
	if ii.combinesBackward() {
	cccB := b[k-1].ccc
	cccC := ii.ccc
	blocked := false // b[i] blocked by starter or greater or equal CCC?
	if cccB == 0 {
	s = k - 1
	} else {
	blocked = s != k-1 && cccB >= cccC
	}
	if !blocked {
	combined := combine(rb.runeAt(s), rb.runeAt(i))
	if combined != 0 {
	rb.assignRune(s, combined)
	continue
	}
	}
	}
	b[k] = b[i]
	k++
	}
	rb.nrune = k
	}