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decentral1se
2024-08-04 11:06:58 +02:00
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vendor/github.com/rivo/uniseg/step.go generated vendored Normal file
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package uniseg
import "unicode/utf8"
// The bit masks used to extract boundary information returned by [Step].
const (
MaskLine = 3
MaskWord = 4
MaskSentence = 8
)
// The number of bits to shift the boundary information returned by [Step] to
// obtain the monospace width of the grapheme cluster.
const ShiftWidth = 4
// The bit positions by which boundary flags are shifted by the [Step] function.
// These must correspond to the Mask constants.
const (
shiftWord = 2
shiftSentence = 3
// shiftwWidth is ShiftWidth above. No mask as these are always the remaining bits.
)
// The bit positions by which states are shifted by the [Step] function. These
// values must ensure state values defined for each of the boundary algorithms
// don't overlap (and that they all still fit in a single int). These must
// correspond to the Mask constants.
const (
shiftWordState = 4
shiftSentenceState = 9
shiftLineState = 13
shiftPropState = 21 // No mask as these are always the remaining bits.
)
// The bit mask used to extract the state returned by the [Step] function, after
// shifting. These values must correspond to the shift constants.
const (
maskGraphemeState = 0xf
maskWordState = 0x1f
maskSentenceState = 0xf
maskLineState = 0xff
)
// Step returns the first grapheme cluster (user-perceived character) found in
// the given byte slice. It also returns information about the boundary between
// that grapheme cluster and the one following it as well as the monospace width
// of the grapheme cluster. There are three types of boundary information: word
// boundaries, sentence boundaries, and line breaks. This function is therefore
// a combination of [FirstGraphemeCluster], [FirstWord], [FirstSentence], and
// [FirstLineSegment].
//
// The "boundaries" return value can be evaluated as follows:
//
// - boundaries&MaskWord != 0: The boundary is a word boundary.
// - boundaries&MaskWord == 0: The boundary is not a word boundary.
// - boundaries&MaskSentence != 0: The boundary is a sentence boundary.
// - boundaries&MaskSentence == 0: The boundary is not a sentence boundary.
// - boundaries&MaskLine == LineDontBreak: You must not break the line at the
// boundary.
// - boundaries&MaskLine == LineMustBreak: You must break the line at the
// boundary.
// - boundaries&MaskLine == LineCanBreak: You may or may not break the line at
// the boundary.
// - boundaries >> ShiftWidth: The width of the grapheme cluster for most
// monospace fonts where a value of 1 represents one character cell.
//
// This function can be called continuously to extract all grapheme clusters
// from a byte slice, as illustrated in the examples below.
//
// If you don't know which state to pass, for example when calling the function
// for the first time, you must pass -1. For consecutive calls, pass the state
// and rest slice returned by the previous call.
//
// The "rest" slice is the sub-slice of the original byte slice "b" starting
// after the last byte of the identified grapheme cluster. If the length of the
// "rest" slice is 0, the entire byte slice "b" has been processed. The
// "cluster" byte slice is the sub-slice of the input slice containing the
// first identified grapheme cluster.
//
// Given an empty byte slice "b", the function returns nil values.
//
// While slightly less convenient than using the Graphemes class, this function
// has much better performance and makes no allocations. It lends itself well to
// large byte slices.
//
// Note that in accordance with [UAX #14 LB3], the final segment will end with
// a mandatory line break (boundaries&MaskLine == LineMustBreak). You can choose
// to ignore this by checking if the length of the "rest" slice is 0 and calling
// [HasTrailingLineBreak] or [HasTrailingLineBreakInString] on the last rune.
//
// [UAX #14 LB3]: https://www.unicode.org/reports/tr14/#Algorithm
func Step(b []byte, state int) (cluster, rest []byte, boundaries int, newState int) {
// An empty byte slice returns nothing.
if len(b) == 0 {
return
}
// Extract the first rune.
r, length := utf8.DecodeRune(b)
if len(b) <= length { // If we're already past the end, there is nothing else to parse.
var prop int
if state < 0 {
prop = propertyGraphemes(r)
} else {
prop = state >> shiftPropState
}
return b, nil, LineMustBreak | (1 << shiftWord) | (1 << shiftSentence) | (runeWidth(r, prop) << ShiftWidth), grAny | (wbAny << shiftWordState) | (sbAny << shiftSentenceState) | (lbAny << shiftLineState) | (prop << shiftPropState)
}
// If we don't know the state, determine it now.
var graphemeState, wordState, sentenceState, lineState, firstProp int
remainder := b[length:]
if state < 0 {
graphemeState, firstProp, _ = transitionGraphemeState(state, r)
wordState, _ = transitionWordBreakState(state, r, remainder, "")
sentenceState, _ = transitionSentenceBreakState(state, r, remainder, "")
lineState, _ = transitionLineBreakState(state, r, remainder, "")
} else {
graphemeState = state & maskGraphemeState
wordState = (state >> shiftWordState) & maskWordState
sentenceState = (state >> shiftSentenceState) & maskSentenceState
lineState = (state >> shiftLineState) & maskLineState
firstProp = state >> shiftPropState
}
// Transition until we find a grapheme cluster boundary.
width := runeWidth(r, firstProp)
for {
var (
graphemeBoundary, wordBoundary, sentenceBoundary bool
lineBreak, prop int
)
r, l := utf8.DecodeRune(remainder)
remainder = b[length+l:]
graphemeState, prop, graphemeBoundary = transitionGraphemeState(graphemeState, r)
wordState, wordBoundary = transitionWordBreakState(wordState, r, remainder, "")
sentenceState, sentenceBoundary = transitionSentenceBreakState(sentenceState, r, remainder, "")
lineState, lineBreak = transitionLineBreakState(lineState, r, remainder, "")
if graphemeBoundary {
boundary := lineBreak | (width << ShiftWidth)
if wordBoundary {
boundary |= 1 << shiftWord
}
if sentenceBoundary {
boundary |= 1 << shiftSentence
}
return b[:length], b[length:], boundary, graphemeState | (wordState << shiftWordState) | (sentenceState << shiftSentenceState) | (lineState << shiftLineState) | (prop << shiftPropState)
}
if firstProp == prExtendedPictographic {
if r == vs15 {
width = 1
} else if r == vs16 {
width = 2
}
} else if firstProp != prRegionalIndicator && firstProp != prL {
width += runeWidth(r, prop)
}
length += l
if len(b) <= length {
return b, nil, LineMustBreak | (1 << shiftWord) | (1 << shiftSentence) | (width << ShiftWidth), grAny | (wbAny << shiftWordState) | (sbAny << shiftSentenceState) | (lbAny << shiftLineState) | (prop << shiftPropState)
}
}
}
// StepString is like [Step] but its input and outputs are strings.
func StepString(str string, state int) (cluster, rest string, boundaries int, newState int) {
// An empty byte slice returns nothing.
if len(str) == 0 {
return
}
// Extract the first rune.
r, length := utf8.DecodeRuneInString(str)
if len(str) <= length { // If we're already past the end, there is nothing else to parse.
prop := propertyGraphemes(r)
return str, "", LineMustBreak | (1 << shiftWord) | (1 << shiftSentence) | (runeWidth(r, prop) << ShiftWidth), grAny | (wbAny << shiftWordState) | (sbAny << shiftSentenceState) | (lbAny << shiftLineState)
}
// If we don't know the state, determine it now.
var graphemeState, wordState, sentenceState, lineState, firstProp int
remainder := str[length:]
if state < 0 {
graphemeState, firstProp, _ = transitionGraphemeState(state, r)
wordState, _ = transitionWordBreakState(state, r, nil, remainder)
sentenceState, _ = transitionSentenceBreakState(state, r, nil, remainder)
lineState, _ = transitionLineBreakState(state, r, nil, remainder)
} else {
graphemeState = state & maskGraphemeState
wordState = (state >> shiftWordState) & maskWordState
sentenceState = (state >> shiftSentenceState) & maskSentenceState
lineState = (state >> shiftLineState) & maskLineState
firstProp = state >> shiftPropState
}
// Transition until we find a grapheme cluster boundary.
width := runeWidth(r, firstProp)
for {
var (
graphemeBoundary, wordBoundary, sentenceBoundary bool
lineBreak, prop int
)
r, l := utf8.DecodeRuneInString(remainder)
remainder = str[length+l:]
graphemeState, prop, graphemeBoundary = transitionGraphemeState(graphemeState, r)
wordState, wordBoundary = transitionWordBreakState(wordState, r, nil, remainder)
sentenceState, sentenceBoundary = transitionSentenceBreakState(sentenceState, r, nil, remainder)
lineState, lineBreak = transitionLineBreakState(lineState, r, nil, remainder)
if graphemeBoundary {
boundary := lineBreak | (width << ShiftWidth)
if wordBoundary {
boundary |= 1 << shiftWord
}
if sentenceBoundary {
boundary |= 1 << shiftSentence
}
return str[:length], str[length:], boundary, graphemeState | (wordState << shiftWordState) | (sentenceState << shiftSentenceState) | (lineState << shiftLineState) | (prop << shiftPropState)
}
if firstProp == prExtendedPictographic {
if r == vs15 {
width = 1
} else if r == vs16 {
width = 2
}
} else if firstProp != prRegionalIndicator && firstProp != prL {
width += runeWidth(r, prop)
}
length += l
if len(str) <= length {
return str, "", LineMustBreak | (1 << shiftWord) | (1 << shiftSentence) | (width << ShiftWidth), grAny | (wbAny << shiftWordState) | (sbAny << shiftSentenceState) | (lbAny << shiftLineState) | (prop << shiftPropState)
}
}
}