Source: composition.go in package golang.org/x/text/unicode/norm


package norm

import "unicode/utf8"

const (

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

Indicates a rune was successfully added to the segment.

Indicates a rune starts a new segment and should not be added.

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

first inserts the first rune of a segment. It is a faster version of next if it is known p represents the first rune in a segment.

func (ss *streamSafe) first(p Properties) {
	*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 = streamSafe(p.nTrailingNonStarters())
		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
}

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

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)
	}

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 {

As the streamSafe accounting already handles the counting for modifiers, we don't have to call next. However, we do need to keep the accounting intact when flushing the buffer.

	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.

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 https://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 https://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
		}

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 &&

11xx plus 116x to LV

				rb.assignRune(s, hangulBase+
					(l-jamoLBase)*jamoVTCount+(v-jamoVBase)*jamoTCount)
			case hangulBase <= l && l < hangulEnd &&
				jamoTBase < v && v < jamoTEnd &&

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.

Lazily load the map used by the combine func below, but do it outside of the loop.

	recompMapOnce.Do(buildRecompMap)

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++ {

Redo from start in Hangul mode. Necessary to support U+320E..U+321E in NFKC mode.

			rb.combineHangul(s, i, k)
			return
		}

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