--- /dev/null
+// 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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