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