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84 lines
3.1 KiB
84 lines
3.1 KiB
// Copyright 2015 The Go Authors. All rights reserved.
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// Use of this source code is governed by a BSD-style
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// license that can be found in the LICENSE file.
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package cases
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func (c info) cccVal() info {
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if c&exceptionBit != 0 {
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return info(exceptions[c>>exceptionShift]) & cccMask
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}
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return c & cccMask
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}
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func (c info) cccType() info {
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ccc := c.cccVal()
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if ccc <= cccZero {
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return cccZero
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}
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return ccc
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}
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// TODO: Implement full Unicode breaking algorithm:
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// 1) Implement breaking in separate package.
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// 2) Use the breaker here.
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// 3) Compare table size and performance of using the more generic breaker.
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//
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// Note that we can extend the current algorithm to be much more accurate. This
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// only makes sense, though, if the performance and/or space penalty of using
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// the generic breaker is big. Extra data will only be needed for non-cased
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// runes, which means there are sufficient bits left in the caseType.
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// Also note that the standard breaking algorithm doesn't always make sense
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// for title casing. For example, a4a -> A4a, but a"4a -> A"4A (where " stands
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// for modifier \u0308).
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// ICU prohibits breaking in such cases as well.
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// For the purpose of title casing we use an approximation of the Unicode Word
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// Breaking algorithm defined in Annex #29:
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// http://www.unicode.org/reports/tr29/#Default_Grapheme_Cluster_Table.
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//
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// For our approximation, we group the Word Break types into the following
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// categories, with associated rules:
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//
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// 1) Letter:
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// ALetter, Hebrew_Letter, Numeric, ExtendNumLet, Extend.
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// Rule: Never break between consecutive runes of this category.
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//
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// 2) Mid:
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// Format, MidLetter, MidNumLet, Single_Quote.
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// (Cf. case-ignorable: MidLetter, MidNumLet or cat is Mn, Me, Cf, Lm or Sk).
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// Rule: Don't break between Letter and Mid, but break between two Mids.
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//
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// 3) Break:
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// Any other category, including NewLine, CR, LF and Double_Quote. These
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// categories should always result in a break between two cased letters.
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// Rule: Always break.
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//
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// Note 1: the Katakana and MidNum categories can, in esoteric cases, result in
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// preventing a break between two cased letters. For now we will ignore this
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// (e.g. [ALetter] [ExtendNumLet] [Katakana] [ExtendNumLet] [ALetter] and
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// [ALetter] [Numeric] [MidNum] [Numeric] [ALetter].)
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//
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// Note 2: the rule for Mid is very approximate, but works in most cases. To
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// improve, we could store the categories in the trie value and use a FA to
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// manage breaks. See TODO comment above.
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//
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// Note 3: according to the spec, it is possible for the Extend category to
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// introduce breaks between other categories grouped in Letter. However, this
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// is undesirable for our purposes. ICU prevents breaks in such cases as well.
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// isBreak returns whether this rune should introduce a break.
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func (c info) isBreak() bool {
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return c.cccVal() == cccBreak
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}
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// isLetter returns whether the rune is of break type ALetter, Hebrew_Letter,
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// Numeric, ExtendNumLet, or Extend.
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func (c info) isLetter() bool {
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ccc := c.cccVal()
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if ccc == cccZero {
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return !c.isCaseIgnorable()
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}
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return ccc != cccBreak
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}
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