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146 lines
3.6 KiB
Go
146 lines
3.6 KiB
Go
// Copyright 2012 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 colltab
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import "unicode/utf8"
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// For a description of ContractTrieSet, see text/collate/build/contract.go.
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type ContractTrieSet []struct{ L, H, N, I uint8 }
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// ctScanner is used to match a trie to an input sequence.
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// A contraction may match a non-contiguous sequence of bytes in an input string.
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// For example, if there is a contraction for <a, combining_ring>, it should match
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// the sequence <a, combining_cedilla, combining_ring>, as combining_cedilla does
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// not block combining_ring.
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// ctScanner does not automatically skip over non-blocking non-starters, but rather
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// retains the state of the last match and leaves it up to the user to continue
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// the match at the appropriate points.
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type ctScanner struct {
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states ContractTrieSet
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s []byte
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n int
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index int
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pindex int
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done bool
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}
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type ctScannerString struct {
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states ContractTrieSet
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s string
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n int
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index int
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pindex int
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done bool
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}
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func (t ContractTrieSet) scanner(index, n int, b []byte) ctScanner {
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return ctScanner{s: b, states: t[index:], n: n}
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}
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func (t ContractTrieSet) scannerString(index, n int, str string) ctScannerString {
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return ctScannerString{s: str, states: t[index:], n: n}
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}
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// result returns the offset i and bytes consumed p so far. If no suffix
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// matched, i and p will be 0.
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func (s *ctScanner) result() (i, p int) {
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return s.index, s.pindex
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}
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func (s *ctScannerString) result() (i, p int) {
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return s.index, s.pindex
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}
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const (
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final = 0
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noIndex = 0xFF
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)
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// scan matches the longest suffix at the current location in the input
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// and returns the number of bytes consumed.
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func (s *ctScanner) scan(p int) int {
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pr := p // the p at the rune start
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str := s.s
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states, n := s.states, s.n
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for i := 0; i < n && p < len(str); {
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e := states[i]
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c := str[p]
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// TODO: a significant number of contractions are of a form that
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// cannot match discontiguous UTF-8 in a normalized string. We could let
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// a negative value of e.n mean that we can set s.done = true and avoid
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// the need for additional matches.
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if c >= e.L {
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if e.L == c {
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p++
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if e.I != noIndex {
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s.index = int(e.I)
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s.pindex = p
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}
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if e.N != final {
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i, states, n = 0, states[int(e.H)+n:], int(e.N)
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if p >= len(str) || utf8.RuneStart(str[p]) {
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s.states, s.n, pr = states, n, p
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}
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} else {
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s.done = true
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return p
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}
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continue
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} else if e.N == final && c <= e.H {
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p++
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s.done = true
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s.index = int(c-e.L) + int(e.I)
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s.pindex = p
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return p
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}
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}
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i++
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}
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return pr
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}
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// scan is a verbatim copy of ctScanner.scan.
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func (s *ctScannerString) scan(p int) int {
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pr := p // the p at the rune start
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str := s.s
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states, n := s.states, s.n
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for i := 0; i < n && p < len(str); {
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e := states[i]
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c := str[p]
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// TODO: a significant number of contractions are of a form that
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// cannot match discontiguous UTF-8 in a normalized string. We could let
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// a negative value of e.n mean that we can set s.done = true and avoid
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// the need for additional matches.
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if c >= e.L {
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if e.L == c {
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p++
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if e.I != noIndex {
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s.index = int(e.I)
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s.pindex = p
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}
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if e.N != final {
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i, states, n = 0, states[int(e.H)+n:], int(e.N)
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if p >= len(str) || utf8.RuneStart(str[p]) {
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s.states, s.n, pr = states, n, p
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}
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} else {
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s.done = true
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return p
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}
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continue
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} else if e.N == final && c <= e.H {
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p++
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s.done = true
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s.index = int(c-e.L) + int(e.I)
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s.pindex = p
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return p
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}
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}
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i++
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}
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return pr
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}
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