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243 lines
9.5 KiB
Go
243 lines
9.5 KiB
Go
package uniseg
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import "unicode/utf8"
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// The bit masks used to extract boundary information returned by [Step].
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const (
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MaskLine = 3
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MaskWord = 4
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MaskSentence = 8
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)
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// The number of bits to shift the boundary information returned by [Step] to
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// obtain the monospace width of the grapheme cluster.
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const ShiftWidth = 4
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// The bit positions by which boundary flags are shifted by the [Step] function.
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// These must correspond to the Mask constants.
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const (
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shiftWord = 2
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shiftSentence = 3
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// shiftwWidth is ShiftWidth above. No mask as these are always the remaining bits.
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)
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// The bit positions by which states are shifted by the [Step] function. These
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// values must ensure state values defined for each of the boundary algorithms
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// don't overlap (and that they all still fit in a single int). These must
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// correspond to the Mask constants.
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const (
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shiftWordState = 4
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shiftSentenceState = 9
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shiftLineState = 13
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shiftPropState = 21 // No mask as these are always the remaining bits.
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)
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// The bit mask used to extract the state returned by the [Step] function, after
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// shifting. These values must correspond to the shift constants.
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const (
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maskGraphemeState = 0xf
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maskWordState = 0x1f
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maskSentenceState = 0xf
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maskLineState = 0xff
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)
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// Step returns the first grapheme cluster (user-perceived character) found in
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// the given byte slice. It also returns information about the boundary between
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// that grapheme cluster and the one following it as well as the monospace width
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// of the grapheme cluster. There are three types of boundary information: word
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// boundaries, sentence boundaries, and line breaks. This function is therefore
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// a combination of [FirstGraphemeCluster], [FirstWord], [FirstSentence], and
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// [FirstLineSegment].
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//
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// The "boundaries" return value can be evaluated as follows:
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//
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// - boundaries&MaskWord != 0: The boundary is a word boundary.
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// - boundaries&MaskWord == 0: The boundary is not a word boundary.
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// - boundaries&MaskSentence != 0: The boundary is a sentence boundary.
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// - boundaries&MaskSentence == 0: The boundary is not a sentence boundary.
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// - boundaries&MaskLine == LineDontBreak: You must not break the line at the
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// boundary.
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// - boundaries&MaskLine == LineMustBreak: You must break the line at the
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// boundary.
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// - boundaries&MaskLine == LineCanBreak: You may or may not break the line at
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// the boundary.
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// - boundaries >> ShiftWidth: The width of the grapheme cluster for most
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// monospace fonts where a value of 1 represents one character cell.
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//
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// This function can be called continuously to extract all grapheme clusters
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// from a byte slice, as illustrated in the examples below.
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//
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// If you don't know which state to pass, for example when calling the function
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// for the first time, you must pass -1. For consecutive calls, pass the state
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// and rest slice returned by the previous call.
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//
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// The "rest" slice is the sub-slice of the original byte slice "b" starting
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// after the last byte of the identified grapheme cluster. If the length of the
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// "rest" slice is 0, the entire byte slice "b" has been processed. The
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// "cluster" byte slice is the sub-slice of the input slice containing the
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// first identified grapheme cluster.
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//
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// Given an empty byte slice "b", the function returns nil values.
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//
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// While slightly less convenient than using the Graphemes class, this function
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// has much better performance and makes no allocations. It lends itself well to
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// large byte slices.
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//
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// Note that in accordance with [UAX #14 LB3], the final segment will end with
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// a mandatory line break (boundaries&MaskLine == LineMustBreak). You can choose
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// to ignore this by checking if the length of the "rest" slice is 0 and calling
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// [HasTrailingLineBreak] or [HasTrailingLineBreakInString] on the last rune.
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//
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// [UAX #14 LB3]: https://www.unicode.org/reports/tr14/#Algorithm
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func Step(b []byte, state int) (cluster, rest []byte, boundaries int, newState int) {
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// An empty byte slice returns nothing.
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if len(b) == 0 {
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return
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}
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// Extract the first rune.
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r, length := utf8.DecodeRune(b)
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if len(b) <= length { // If we're already past the end, there is nothing else to parse.
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var prop int
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if state < 0 {
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prop = propertyGraphemes(r)
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} else {
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prop = state >> shiftPropState
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}
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return b, nil, LineMustBreak | (1 << shiftWord) | (1 << shiftSentence) | (runeWidth(r, prop) << ShiftWidth), grAny | (wbAny << shiftWordState) | (sbAny << shiftSentenceState) | (lbAny << shiftLineState) | (prop << shiftPropState)
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}
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// If we don't know the state, determine it now.
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var graphemeState, wordState, sentenceState, lineState, firstProp int
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remainder := b[length:]
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if state < 0 {
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graphemeState, firstProp, _ = transitionGraphemeState(state, r)
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wordState, _ = transitionWordBreakState(state, r, remainder, "")
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sentenceState, _ = transitionSentenceBreakState(state, r, remainder, "")
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lineState, _ = transitionLineBreakState(state, r, remainder, "")
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} else {
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graphemeState = state & maskGraphemeState
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wordState = (state >> shiftWordState) & maskWordState
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sentenceState = (state >> shiftSentenceState) & maskSentenceState
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lineState = (state >> shiftLineState) & maskLineState
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firstProp = state >> shiftPropState
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}
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// Transition until we find a grapheme cluster boundary.
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width := runeWidth(r, firstProp)
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for {
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var (
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graphemeBoundary, wordBoundary, sentenceBoundary bool
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lineBreak, prop int
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)
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r, l := utf8.DecodeRune(remainder)
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remainder = b[length+l:]
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graphemeState, prop, graphemeBoundary = transitionGraphemeState(graphemeState, r)
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wordState, wordBoundary = transitionWordBreakState(wordState, r, remainder, "")
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sentenceState, sentenceBoundary = transitionSentenceBreakState(sentenceState, r, remainder, "")
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lineState, lineBreak = transitionLineBreakState(lineState, r, remainder, "")
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if graphemeBoundary {
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boundary := lineBreak | (width << ShiftWidth)
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if wordBoundary {
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boundary |= 1 << shiftWord
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}
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if sentenceBoundary {
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boundary |= 1 << shiftSentence
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}
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return b[:length], b[length:], boundary, graphemeState | (wordState << shiftWordState) | (sentenceState << shiftSentenceState) | (lineState << shiftLineState) | (prop << shiftPropState)
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}
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if firstProp == prExtendedPictographic {
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if r == vs15 {
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width = 1
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} else if r == vs16 {
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width = 2
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}
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} else if firstProp != prRegionalIndicator && firstProp != prL {
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width += runeWidth(r, prop)
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}
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length += l
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if len(b) <= length {
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return b, nil, LineMustBreak | (1 << shiftWord) | (1 << shiftSentence) | (width << ShiftWidth), grAny | (wbAny << shiftWordState) | (sbAny << shiftSentenceState) | (lbAny << shiftLineState) | (prop << shiftPropState)
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}
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}
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}
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// StepString is like [Step] but its input and outputs are strings.
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func StepString(str string, state int) (cluster, rest string, boundaries int, newState int) {
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// An empty byte slice returns nothing.
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if len(str) == 0 {
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return
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}
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// Extract the first rune.
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r, length := utf8.DecodeRuneInString(str)
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if len(str) <= length { // If we're already past the end, there is nothing else to parse.
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prop := propertyGraphemes(r)
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return str, "", LineMustBreak | (1 << shiftWord) | (1 << shiftSentence) | (runeWidth(r, prop) << ShiftWidth), grAny | (wbAny << shiftWordState) | (sbAny << shiftSentenceState) | (lbAny << shiftLineState)
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}
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// If we don't know the state, determine it now.
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var graphemeState, wordState, sentenceState, lineState, firstProp int
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remainder := str[length:]
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if state < 0 {
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graphemeState, firstProp, _ = transitionGraphemeState(state, r)
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wordState, _ = transitionWordBreakState(state, r, nil, remainder)
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sentenceState, _ = transitionSentenceBreakState(state, r, nil, remainder)
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lineState, _ = transitionLineBreakState(state, r, nil, remainder)
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} else {
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graphemeState = state & maskGraphemeState
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wordState = (state >> shiftWordState) & maskWordState
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sentenceState = (state >> shiftSentenceState) & maskSentenceState
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lineState = (state >> shiftLineState) & maskLineState
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firstProp = state >> shiftPropState
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}
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// Transition until we find a grapheme cluster boundary.
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width := runeWidth(r, firstProp)
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for {
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var (
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graphemeBoundary, wordBoundary, sentenceBoundary bool
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lineBreak, prop int
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)
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r, l := utf8.DecodeRuneInString(remainder)
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remainder = str[length+l:]
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graphemeState, prop, graphemeBoundary = transitionGraphemeState(graphemeState, r)
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wordState, wordBoundary = transitionWordBreakState(wordState, r, nil, remainder)
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sentenceState, sentenceBoundary = transitionSentenceBreakState(sentenceState, r, nil, remainder)
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lineState, lineBreak = transitionLineBreakState(lineState, r, nil, remainder)
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if graphemeBoundary {
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boundary := lineBreak | (width << ShiftWidth)
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if wordBoundary {
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boundary |= 1 << shiftWord
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}
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if sentenceBoundary {
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boundary |= 1 << shiftSentence
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}
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return str[:length], str[length:], boundary, graphemeState | (wordState << shiftWordState) | (sentenceState << shiftSentenceState) | (lineState << shiftLineState) | (prop << shiftPropState)
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}
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if firstProp == prExtendedPictographic {
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if r == vs15 {
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width = 1
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} else if r == vs16 {
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width = 2
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}
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} else if firstProp != prRegionalIndicator && firstProp != prL {
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width += runeWidth(r, prop)
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}
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length += l
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if len(str) <= length {
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return str, "", LineMustBreak | (1 << shiftWord) | (1 << shiftSentence) | (width << ShiftWidth), grAny | (wbAny << shiftWordState) | (sbAny << shiftSentenceState) | (lbAny << shiftLineState) | (prop << shiftPropState)
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}
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}
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}
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